human cell foundation for all life

let us look at a foundation for all life, the cell. Let's look at a human cell, since all of us who will read this will be human, and thus we all have cells in common. Some of us were told in school that cells are a simple structure, however we have learned in the last decade or so that actually cells are extremely complex structures and they even contain complex structures in them!
Here are a few complex parts of cells that are common to every cell in every species.

DNA (Deoxyribonucleic acid) is the molecule that contains the chemical instructions for cells to manufacture various proteins.


Chromosome – a carrier of genes and one of the 46 molecules of DNA. It comes in 23 pairs, and is found in each cell in the human body, together contains all the genes. These chromosomes contain the instructions to make all the proteins that are needed. Other species contain more or fewer chromosomes. One member of each pair of the 23 pairs comes from the gamete of each parent.


Gene – Is the basic unit for the transmission of heredity, consisting of a string of chemicals coding for the manufacture of certain proteins. The instructions from the 46 chromosomes are organized into genes on the chromosome. Each gene is a separate section of a chromosome, and every gene contains instructions for specific proteins. Each gene has chemicals (amino acids) that are paired and then arranged in groups of three (triplets). Genes direct the creation of 20 types of amino acids.

Also consider this:
Human genome – Is the full set of all the 25,000 or so genes on 46 chromosomes that are the instructions for making a human. There is a genome for every species, even plants. Every human except for mono zygotic twins has a slightly different code, otherwise the human genome is 99.99% the same for any two people.

Is there any one out there who can tell me that how by chance amino acids would ever get together and form genes, and then form chromosomes, and then make DNA? Also explain to me why these complex structures whose instructions are specific would randomly do anything, let alone randomly form a whole different creature from what is currently is? The purpose of the DNA of the cell is to guide it to do what needs to be done. A muscular cell does not try to think, nor does a hair cell try to flex. Most cells also reproduce; you do not have blood cells try to make a cell for the stomach. Yes, we do occasionally we have cancer cells, a group of cells that are similar to normal cells yet abnormal and uncontrollably multiply and destroy healthy tissues. However from cancer we do not find another whole species being created. There was a cellular malfunction. This look at cells is a very crude and simple glance; I am not doing it justice. Yet can you deny the complexity of the cell?

How about looking at a different cell, or just one part of a different cell; the flagellum motor of a bacterium. The flagellum is a hair like structure on bacteria that propels a bacterium around.

human embryonic stem cells

Human embryonic stem cells have been cultured under chemically controlled conditions without the use of animal substances, which is essential for future clinical uses. The method has been developed by researchers at Karolinska Institute and is presented in the journal Nature Biotechnology.

Embryonic stem cells can be turned into any other type of cell in the body and have potential uses in treatments where sick cells need to be replaced. One problem, however, is that it is difficult to culture and develop human embryonic stem cells without simultaneously contaminating them. They are currently cultured with the help of proteins from animals, which rules out subsequent use in the treatment of humans. Alternatively the stem cells can be cultured on other human cells, known as feeder cells, but these release thousands of uncontrolled proteins and therefore lead to unreliable research results.

A research team at the Department of Medical Biochemistry and Biophysics, Karolinska Institute has now managed to produce human stem cells entirely without the use of other cells or substances from animals. Instead they are cultured on a matrix of a single human protein: laminin-511.

"Now, for the first time, we can produce large quantities of human embryonic stem cells in an environment that is completely chemically defined," says professor Karl Tryggvason, who led the study.

"This opens up new opportunities for developing different types of cell which can then be tested for the treatment of disease."

Together with researchers at the Harvard Stem Cell Institute, the researchers have also shown that in the same way they can culture what are known as reprogrammed stem cells, which have been converted back from tissue cells to stem cells.

Laminin-511 is part of our connective tissue and acts in the body as a matrix to which cells can attach. In the newly formed embryo, the protein is also needed to keep stem cells as stem cells. Once the embryo begins to develop different types of tissue, other types of laminin are needed.

Until now, different types of laminin have not been available to researchers, because they are almost impossible to extract from tissues and difficult to produce. Over the last couple of decades, Karl Tryggvason’s research group has cloned the genes for most human laminins, studied their biological role, described two genetic laminin diseases and, in recent years, even managed to produce several types of laminin using gene technology. In this latest experiment, the researchers produced the laminin-511 using recombinant techniques.

Subcellular components of Cell

All cells, whether prokaryotic or eukaryotic, have a membrane that envelops the cell, separates its interior from its environment, regulates what moves in and out (selectively permeable), and maintains the electric potential of the cell. Inside the membrane, a salty cytoplasm takes up most of the cell volume. All cells possess DNA, the hereditary material of genes, and RNA, containing the information necessary to build various proteins such as enzymes, the cell's primary machinery. There are also other kinds of biomolecules in cells. This article will list these primary components of the cell, then briefly describe their function.

Cell membrane: A cell's defining boundary
The cytoplasm of a cell is surrounded by a plasma membrane. The plasma membrane in plants and prokaryotes is usually covered by a cell wall. This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of lipids (hydrophobic fat-like molecules) and hydrophilic phosphorus molecules. Hence, the layer is called a phospholipid bilayer. It may also be called a fluid mosaic membrane. Embedded within this membrane is a variety of protein molecules that act as channels and pumps that move different molecules into and out of the cell. The membrane is said to be 'semi-permeable', in that it can either let a substance (molecule or ion) pass through freely, pass through to a limited extent or not pass through at all. Cell surface membranes also contain receptor proteins that allow cells to detect external signalling molecules such as hormones.

Cytoskeleton: A cell's scaffold
The cytoskeleton acts to organize and maintain the cell's shape; anchors organelles in place; helps during endocytosis, the uptake of external materials by a cell, and cytokinesis, the separation of daughter cells after cell division; and moves parts of the cell in processes of growth and mobility. The eukaryotic cytoskeleton is composed of microfilaments, intermediate filaments and microtubules. There is a great number of proteins associated with them, each controlling a cell's structure by directing, bundling, and aligning filaments. The prokaryotic cytoskeleton is less well-studied but is involved in the maintenance of cell shape, polarity and cytokinesis.
Genetic material
Two different kinds of genetic material exist: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Most organisms use DNA for their long-term information storage, but some viruses (e.g., retroviruses) have RNA as their genetic material. The biological information contained in an organism is encoded in its DNA or RNA sequence. RNA is also used for information transport (e.g., mRNA) and enzymatic functions (e.g., ribosomal RNA) in organisms that use DNA for the genetic code itself.
Prokaryotic genetic material is organized in a simple circular DNA molecule (the bacterial chromosome) in the nucleoid region of the cytoplasm. Eukaryotic genetic material is divided into different, linear molecules called chromosomes inside a discrete nucleus, usually with additional genetic material in some organelles like mitochondria and chloroplasts (see endosymbiotic theory).
A human cell has genetic material in the nucleus (the nuclear genome) and in the mitochondria (the mitochondrial genome). In humans the nuclear genome is divided into 46 linear DNA molecules called chromosomes. The mitochondrial genome is a circular DNA molecule separate from the nuclear DNA. Although the mitochondrial genome is very small, it codes for some important proteins.
Foreign genetic material (most commonly DNA) can also be artificially introduced into the cell by a process called transfection. This can be transient, if the DNA is not inserted into the cell's genome, or stable, if it is.

Organelles
The human body contains many different organs, such as the heart, lung, and kidney, with each organ performing a different function. Cells also have a set of "little organs," called organelles, that are adapted and/or specialized for carrying out one or more vital functions. Membrane-bound organelles are found only in eukaryotes.
Credit by Wikipedia

RNA comparison with DNA

RNA and DNA differ in three main ways. First, unlike DNA which is double-stranded, RNA is a single-stranded molecule in most of its biological roles and has a much shorter chain of nucleotides. Secondly, while DNA contains deoxyribonucleic acid, RNA contains ribonucleic acid, (there is no hydroxyl group attached to the pentose ring in the 2' position in DNA, whereas RNA has two hydroxyl groups). These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. In light of this, several types of RNA (tRNA, rRNA) contain a great deal of secondary structure, which help promote stability. Thirdly, the base-pair of adenine is not thymine, as it is in DNA, but rather uracil, which is a unmethylated form of thymine.
Like DNA, most biologically active RNAs including tRNA, rRNA, snRNAs and other non-coding RNAs (such as the SRP RNAs) are extensively base paired to form double stranded helices. Structural analysis of these RNAs have revealed that they are not, "single-stranded" but rather highly structured. Unlike DNA, this structure is not just limited to long double-stranded helices but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical catalysis, like enzymes. For instance, determination of the structure of the ribosome in 2000 revealed that the active site of this enzyme that catalyzes peptide bond formation is composed entirely of RNA.

Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. So to say, it is the transfer of genetic information from DNA into RNA. In the case of protein-encoding DNA, transcription is the beginning of the process that ultimately leads to the translation of the genetic code (via the mRNA intermediate) into a functional peptide or protein. The stretch of DNA that is transcribed into an RNA molecule is called a transcription unit. Transcription has some proofreading mechanisms, but they are fewer and less effective than the controls for copying DNA; therefore, transcription has a lower copying fidelity than DNA replication.[citation needed]
As in DNA replication, transcription proceeds in the 5' → 3' direction (i.e. the old polymer is read in the 3' → 5' direction and the new, complementary fragments are generated in the 5' → 3' direction). Transcription is divided into 3 stages: initiation, elongation and termination.

DNA and RNA Introduction

Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organism. The main role of DNA is the long-term storage of information and it is often compared to a set of blueprints, since DNA contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information. Chemically, DNA is a long polymer of simple units called nucleotides, with a backbone made of sugars and phosphate atoms joined by ester bonds. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription. Most of these RNA molecules are used to synthesize proteins, but others are used directly in structures such as ribosomes and spliceosomes.

Within cells, DNA is organized into structures called chromosomes and the set of chromosomes within a cell make up a genome. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms such as animals, plants, and fungi store their DNA inside the cell nucleus, while in prokaryotes such as bacteria it is found in the cell's cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA, which helps control its interactions with other proteins and thereby control which genes are transcribed.

Ribonucleic acid or RNA is a nucleic acid polymer consisting of nucleotide monomers that plays several important roles in the processes that translate genetic information from deoxyribonucleic acid (DNA) into protein products; RNA acts as a messenger between DNA and the protein synthesis complexes known as ribosomes, forms vital portions of ribosomes, and acts as an essential carrier molecule for amino acids to be used in protein synthesis.
RNA is very similar to DNA, but differs in a few important structural details: RNA nucleotides contain ribose sugars while DNA contains deoxyribose and RNA uses predominantly uracil instead of thymine present in DNA. RNA is transcribe (synthesize) from DNA by enzymes called RNA polymerases and further processed by other enzymes. RNA serves as the template for translation of genes into proteins, transferring amino acids to the ribosome to form proteins, and also translating the transcript into proteins. Nucleic acids were discovered in 1868 (some sources indicate 1869) by Johann Friedrich Miescher (1844-1895), who called the material 'nuclein' since it was found in the nucleus. It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids. The role of RNA in protein synthesis had been suspected since 1939, based on experiments carried out by Torbjörn Caspersson, Jean Brachet and Jack Schultz. Hubert Chantrenne elucidated the messenger role played by RNA in the synthesis of proteins in ribosome. The sequence of the 77 nucleotides of a yeast RNA was found by Robert W. Holley in 1964, winning Holley the 1968 Nobel Prize for Medicine. In 1976, Walter Fiers and his team at the University of Ghent determined the complete nucleotide sequence of bacteriophage MS2-RNA.

DNA and RNA Structure and Functions

DNA (deoxyribonucleic acid) is the genetic material and is largely found in the chromosomes. RNA (ribonucleic acid) is made up of nucleotides containing sugar ribose. When these two work together, they build the amino acid sequence in a protein. This section is going to look at them individually.

DNA

Here is the structure of a DNA. As many have heard, or possibly made models of, the DNA is a double helix. This simply means it has two strands that spiral around each other. In the middle of these strands are nucleotides that are bonded by hydrogen bonding. The bonds created are: A with T, and G with C. These are called complimentary paired bases.

The function of DNA is to replicate. Its job is to make an exact replica of itself. The fancy scientific term for this process is called: DNA replication. Here is a brief explanation of how DNA replicates. This is pulled straight from our text book, but I found it to be the simplest and most clear.

   1. Before replication starts, the two strands of the original DNA are hydrogen-bonded together.
   2. An enzyme unwinds and “unzips” the DNA
   3. New complementary DNA nucleotides, which are always in the nucleus, fit into place by the process of complimentary base pairing. These position and are then joined by the enzyme DNA polymerase.
   4. To complete replication, an enzyme seals any breaks in the sugar-phosphate backbone
   5. The two double-helix molecules are identical to each other and the original DNA.

RNA

Now for an RNA structure. We now know that DNA is made up of the A,T,G, and, C nucleotides. RNA, on the other hand, is made up of C,G,A, an U nucleotides. RNA is also single stranded. There are also three types of RNA.

The first is Ribosomal RNA or rRNA. It is produced in the nucleolus and its main job is to join with proteins made in the cytoplasm to form the subunits of ribosomes.

Structure of DNA and RNA molecules

We know that all organisms produce offsprings of their own kind whether it is a single celled animal like Amoeba or a multicellular animal like a horse. Amoeba produces a daughter amoeba, and a horse produces a baby horse. All this is possible just because a very special molecule that is termed as deoxyribonucleic acid or DNA. The DNA contains the hereditary material which makes every individual unique and this material is transferred from the parents to the offsprings. The DNA is present in a special organelle of the cell called the nucleus. As the size of the cell is very small and each organism has many molecules of DNA so the DNA must be tightly packed inside the nucleus and this packed form of DNA is called as chromosome. DNA spends it most of the time inside the cell in the form of chromosome. During cell division, the DNA unwinds so that it can be copied and transferred to the daughter cells. DNA also carries instructions for protein synthesis so that other biological processes can be regulated normally. The DNA present inside the nucleus is termed as nuclear DNA and the complete set of nuclear DNA is designated as genome. Apart from its occurrence inside the nucleus, DNA is also present in the cell organelle named as mitochondria which are the power houses of the cells. During sexual reproduction the offsprings inherit half of the nuclear DNA from the father and half from the mother but the mitochondrial DNA is inherited completely from the mother as the sperm cells do not bear mitochondria after fertilization.

The DNA molecule was first observed in the late 1800s by a German biochemist Frederich Miescher. But nearly a century passed after that and the scientists couldn't succeed in unraveling the mystery of the DNA molecule. The mystery of the DNA was solved in 1953 by the eminent works of James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin. By using X-ray diffraction technique the scientists pointed out the double helical structure of DNA that encodes the genetic information of every organism living on this earth.

The chemical building blocks of DNA are called as nucleotides. The nucleotides are formed of three components: a phosphate group, a sugar and one of the four types of nitrogenous bases. To form a complete strand of DNA nucleotides are linked in the form of chains with alternating arrangement of phosphate groups and sugars. The four types of nucleotide bases that form DNA are adenine (A), guanine (G), cytosine (C) and Thymine (T). The arrangement of these nitrogenous bases within a DNA molecule is very specific. The adenine can always pair with thymine on one side of the DNA helix and cytosine can also pair with guanine on one side of the DNA helix. This specific arrangement of base pairs in a DNA strand follows a rule called as Chargaff's rule which plays a very important role in the replication of the DNA molecule.

The process of DNA replication proceeds after the breaking of the weak chemical bonds between the two poly nucleotide chains by an enzyme. The DNA strand breaks in the middle separating the base pairs. These newly separated strands now work as templates from which the new strands of DNA will be obtained. Inside the nucleus many extra nucleotides are present. The bases first bond with the bases present on the template which will match just according to the Chargaff's rule. When the base pairing is completed the phosphate groups and the sugar is added to form other poly nucleotide chain. This procedure is repeated with both the template strands of DNA. The whole process is repeated thousands of time in order to form the two molecules of DNA which are exactly the replicates of the original DNA molecule and all this happens during mitosis so the daughter cells receive the exact similar character of the DNA. When an error occurs during the process of DNA replication mutation occurs. The mutation causes either deletion or addition of base pairs and the proteins also get defected by having wrong pairs of amino acids.

One of the important functions of DNA is protein synthesis. The process of protein synthesis is completed in two steps. The first step is transcription and the second step is translation. In transcription the cell uses the information from a gene in order to form a protein. Both the DNA and RNA molecules are similar in structure except the fact that RNA is shorter than DNA and bears the sugar ribose instead of deoxyribose that is present in DNA. RNA also differs from DNA in having a base uracil in place of thymine. During transcription, the type of RNA that is created is called mRNA or messenger RNA because it is used as a "messenger" to send information from a gene on DNA to a ribosome so that protein can be created. RNA polymerase recognizes and attaches to a DNA nucleotide chain at the beginning of the gene, at a place called the promoter. The promoter positions the RNA polymerase on the right strand of DNA and guides it to the right direction. As the RNA polymerase moves, it creates a new chain from the extra nucleotides. The RNA polymerase continues until it reaches a stop signal at the end of the gene. The RNA polymerase then detaches itself from the DNA and the RNA chain is released, creating mRNA.

When the mRNA sends the information from the DNA to the ribosomes it is converted into the language of amino acids. When amino acids are formed a protein is created. The mRNA transfers the information from the DNA to the ribosomes in the language of nucleotides. The ribosomes attach on a particular place on the mRNA which is called start codon which is made up of three nucleotide bases indicating that it is ready to read a message. The amino acids that will later form protein come across the transfer RNA or tRNA while they are attached to the ribosomes. The tRNA moves the amino acids along the mRNAs so that the message can feed across the ribosome. There the amino acids are all linked together to form a protein chain. Every organism on uses this process to make proteins.

Thus, it can be concluded that DNA is very essential component of an organism's life.

DNA molecules between telepathy

The latest study, DNA molecules appear to have telepathy. Scientists have discovered the double helix structure of DNA molecules to identify themselves with the "matching" elements, even some distance away, on the surface and no other outside help, the match of the two elements together to the end. In accordance with the previous understanding of DNA, scientists study the double helix structure of DNA molecules are arranged in accordance with the laws of their own. Helix structure of DNA molecule is composed of many ODN from the polymerization of long-chain, as the composition of the DNA base pairs of only four: adenine (A), guanine (G), cytosine (C) And thymine (T), therefore, there are four types of DNA, we usually A, T, C, G Four alphabet tag them, and use of chemical methods to match their children - A equipped with T, C equipped with G . In fact, the well-known "to exchange the role of the base together" is not the DNA double helix molecule in close connection with the bodies of the root causes. The DNA double helix structure was so stable, because the outside of deoxyribose phosphate and arranged in alternating the basic framework, the inside of the base to form hydrogen bonds through the base right. Scientists study the mixture through the fluorescence of this double-stranded DNA molecule structure. These DNA molecules were placed on some of the salt water, salt water test does not contain any proteins, DNA molecules will enable non-binding, as well as any material that may affect the trial. Strangely enough, together with the same number of base pairs of DNA molecules is the other remaining twice the number of DNA molecules. Even though they look like a very strange, like a psychological sense, but in fact only a DNA molecule in the exercise under the laws of physics, not a supernatural phenomenon. Take charge of deoxyribose and phosphate arranged in turn composed of DNA molecules will be mutually exclusive, however, because of the DNA double helix structure of the special, making the repulsive force between them to reach the minimum. In order to understand more vividly the researchers said, let us try the double helix structure of DNA molecules into a corkscrew imagination to form a long chain of DNA molecules in the base of support outside the framework and the role of hydrogen bonds in the middle of, So that the screw cone to the direction of a distorted, twisted into a spiral, then the process will be part of the same degree of bending and other elements of the sunken part of the coordinated combination. Scientists point out that this "psychological sense" would help the DNA molecules in the chaos of their pre-arranged neatly, which can effectively avoid errors occur when the combination of DNA, it effectively avoiding cancer, aging and other diseases. However, due to the same DNA sequence in fact disrupt the combination of sexual reproduction is a meaningful, because of the need to ensure that future generations have the genetic diversity.

RNA extraction from tissues

Procedures for RNA extraction from tissues :

1. pre-weigh an empty cryovial
2. take the tissue specimen out from the cryovial and place it on a 100mm petri dish
3. use a scapel and sterican (like fork and knife) to cut the tissue into desired size
4. transfer the tissue into the pre-weigh cryovial and weigh again (this will give the exact weigh of the tissue being process)
5. transfer the surplus tissue into the original cryovial and keep in the nitrogen tank
6. add 650µl of RLT buffer into the cryovial
7. pound the tissue using a pipette tip until the solution turn orange in colour.
8. transfer the solution into QIA shredder column and centrifuge at 14 000rpm for 4minutes
9. transfer the flow through into a new eppendorf tube and add in 550µl of 70% ethanol
10. centrifuge the eppendorf tube at 14 000rpm for 3 minutes
11. transfer the solution into Rneasy column and centrifuge at 14 000rpm for 15 seconds
12. discard the flow through
13. add 700µl RW1 buffer into the Rneasy column and centrifuge at 14 000rpm for 15 seconds
14. discard the flow through
15. add 500µl RPE buffer into the Rneasy column and centrifuge at 14 000rpm for 15 seconds
16. discard the flow through
17. centrifuge the Rneasy column at 14 000rpm for 1 minute
18. transfer the Rneasy column into a new sterilised round bottom tube
19. add 30µl Rnase-free water and centrifuge at 14 000rpm for 1 minute
20. transfer the flow into the column and centrifuge at 14 000rpm for 1 minute
21. the flow through is the RNA extracted

Thing to note
- after taking the cryovial of tissue out from the nitrogen tank, keep it in liquid nitrogen.

The structure of dna

DNA is composed of many DNA residue, according to a certain order each other with 3 ', 5'-phosphate ester linked to the composition of long chain. DNA contains a majority of two such long-chain, and some for single-stranded DNA, such as E. coli phage φX174, G4, M13 and so on. Some DNA for the ring, and some for the linear DNA. Contains adenine, guanine, thymine and cytosine base 4. In some types of DNA, 5 - cytosine methylation may to a certain extent replaced by cytosine, wheat germ DNA of the 5 - cytosine-rich in particular, up to 6% of the mole. In some phage, 5 - hydroxymethyl cytosine replaced cytosine. In the late 40, Gabriel Richard (E. Chargaff) found that different species of the base composition of DNA, but the number of adenine equal to the number of its thymine (A = T), guanine cytosine number equal to the number (G = C), and therefore the number of purine and pyrimidine equal to the number of and. Several described by the general level of the structure of DNA.
A structure of the primary structure of DNA that is its base sequence. Gene is a fragment of DNA, genetic information stored in its base sequence. In 1975 the United States Gilbert (W. Gilbert) and the United Kingdom's Sanger (F. Sanger) respectively, created the structure of the DNA level, the rapid determination of their total end of 1980 Nobel Prize in Chemistry. Since then, the method also has been improved, many of the primary structure of DNA has been established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage DNA contains 48,502 base pairs, rice chloroplast genome contains 134,525 base pairs, tobacco chloroplast genome contains 155,844 base pairs, and so on. Now the United States has plans to 10-15 years in all human DNA molecule of about 3,000,000,000 for the nucleotide sequence out.
Secondary structure in 1953, Watson (Watson) and Crick (Crick) put forward the basic structure of DNA fiber is a double helix structure, then this model has been recognized scientists, and to explain to copy, transcription, and other important life processes. After an in-depth study and found that humidity and as a result of base sequences in different conditions, DNA double helix can have a variety of types, mainly divided into A, B and Z three categories.
It is generally believed, B cells closest to the structure of DNA conformation, it is very similar to the double helix model. A-DNA and RNA molecules in the two-time transcription, as well as the district Screw the formation of the DNA-RNA hybridization close to the molecular conformation. Z-DNA nucleotide dimer to the left to the wound as a unit, which was the main chain saw (Z)-shaped, and named. This configuration for multi-purine nucleotide chains of alternating pyrimidine area. In 1989, U.S. scientists used scanning tunneling electron microscope to directly observe the double helix DNA double helix DNA ︰ 1952, Austria-American biochemist Chargaff (E.chargaff, 1905 -) was determined by DNA base pairs in the 4 Content and found that methotrexate gland and fat equal to the number of thymine, cytosine and methotrexate fat birds of the same number. This Watson, Crick immediately think of base 4 between 22 corresponds to the relationship between the formation of the gland fat and thymine pair methotrexate, methotrexate fat birds and the concept of cytosine pair.

High structure
Triplex DNA (T-DNA)
In the early 1950s, Wilkins According to the X-ray diffraction pictures have been envisaged in the DNA chain may be 3, Crick later watson and others have to build some T-DNA model. Has found that the three DNA chain can be divided into two categories, namely, three helix structure of the Chinese Academy of Sciences and in 1990 by Bai Chunli, such as scanning tunneling electron microscope techniques to observe the structure of the three Fabian "
Three in the spiral structure of DNA double helix structure formed on the basis of the three chains District 3 chain are homologous or homologous pyrimidine purine that the entire base of the pyrimidine purine or, in accordance with section 3 of the chain of sources , The DNA chain can be divided into three elements and between elements within the two groups, according to the 3 components of the chain as well as the relative positions can be divided into Pu-Pu-Py and Py-Pu-Py-two (Pu-generation
Table purine chain, Py pyrimidine on behalf of the chain) is one of the most common Py-Pu-Py type, it's 3 in the chain there are 2 for a normal double helix, 3 pyrimidine chain located in the double helix of the big ditch, Purine with the chain in the same direction and with the double helix structure of the rotation together, the three chains in the base pairs of DNA double helix with the same, that is, their base is still AT, GC matching However, No. 3 chain C must be protonated , And G with only 2 to form hydrogen bonds (normally three hydrogen bonds).
Triplex DNA research will help shed further light on the structure of chromosomes and genes in eukaryotic transcription, replication, and re-regulation and control mechanism. In addition three DNA chain have a certain value, such as the availability of single-stranded DNA fragments will be cutting agent (such as the endonuclease) to carry DNA to a specific site, so as to achieve selective chromosome DNA hit off the end, because the cells Transcription factors such as regulation and protein only after the combination of DNA double helix to open its specific gene transcription, transcription factors can not helical and the three combined, it can make use of oligo DNA fragment closure of the transcription factor binding sites in order to reach the turn off harmful genes or Virus genes.
Quadruplex DNA
Klug and Sundpuist in a simulated 1 kind of spike protozoan telomere DNA of the caterpillar, paragraph 1 of the synthetic DNA sequences and found that under certain conditions, the simulation of G-rich single-stranded DNA to form a quadruplex DNA structure. This chromosome that the end of the telomere single strand between the formation of a four-chain. Kang and others were confirmed by experiments in crystal and in solution, the rich G DNA can form a quadruplex DNA structure.
Quadruplex DNA is the basic structure of the G-quadruplex, that is, in the four conjoined at the center there are 4 by a negative charge with the carboxylic oxygen atoms surrounded the "pocket" through the G-quadruplex accumulation can be Elements to form molecules or between right-handed spiral, with the double helix structure of DNA comparison, G-quadruplex spiral 2 significant characteristics: 1, the stability of its decision in the pocket by the combination of cation type, known ion k The combination of quadruple-helix so that the most stable; 2, and its thermodynamic stability of the very nature and dynamics.
At present some of the biological DNA sequence analysis that the G-rich DNA sequence found in some of the functions and evolution are very conservative region of the genome, many studies have shown that guanine-rich DNA chain formed by G-DNA may be As the mutual recognition between the molecular components of one of the organisms in the cell plays a special role

DNA, RNA and Protein : Life at its simplest

DNA : Deoxyribonucleic acid. The double-stranded chemical instruction manual for everything a plant or animal does: grow, divide, even when and how to die. Very stable, has error detection and repair mechanisms. Stays in the cell nucleus. Can make good copies of itself.
RNA: Ribonucleic acid. Single-stranded where DNA is double-stranded, messenger RNA carries single pages of instructions out of the nucleus to places they're needed throughout the cell. No error detection or repair; makes flawed copies of itself. Evolves ten times faster than DNA. Transfer RNA helps translate the mRNA message into chains of amino acids in the ribosomes.
[Diagram of RNA vs. DNA: chemical structure and composition]

Base: a building block of DNA and RNA. There are five different bases: Adenine, Thymine, Guanine, Cytosine, and Uracil (which is found only in RNA and replaces Thymine in DNA).

Ribosomes: Message centers throughout the cell where the information from DNA arrives in the form of messenger RNA. The RNA message gets translated into a form the ribosome can understand and tells it which protein building blocks it needs and in what order to assemble them. Ribosomal RNA helps the translation go smoothly.

Amino acids: Polypeptide (protein) building blocks.

Polypeptides: chains of amino acids. Proteins are made up of several or many polypeptides.

Proteins: Chemicals that make up cell and organ structure and carry out reactions throughout the body, from breaking down food to fighting off disease.

Technology of Genetic Engineering

Genetic engineering requires three fundamental technologies: the ability to isolate and modify the DNA of specific individual genes; an understanding of the mechanisms that regulate how genes function and how these can be manipulated; and the capacity to transfer genes into an organism. These have all been developed following the discovery of the structure of DNA in 1953. Genetic engineering of microbes was first reported in 1973, followed in the next decade by similar achievements in plants and animals. Because DNA is the genetic material in all organisms, genes for genetic engineering can be taken from any source, or even synthesized. Modification of genes may be necessary, particularly in regions that control how they operate, in order for the genes to function effectively in the recipient organism. Agrobacterium tumefaciens, a bacterium that transfers DNA into plant cells as part of its normal life cycle, is used commonly to transfer genes into plants, although other methods such as the "gene gun" also have been developed. Genetically engineered plants are technically "transgenic organisms," as they contain transferred genes. However, they are frequently referred to as "genetically modified organisms," or GMOs, and the products derived from them are described as "genetically modified," or GM foods. These terms can be confusing, as essentially all cultivated plants have been genetically modified through breeding and selection—for example, the many varieties of cultivated onions possess numerous qualities that distinguish them from each other and especially from the wild onions from which they originated.

Application of Genetic Engineering in Agriculture

The first genetically engineered crops were planted on a large scale in 1996. By 2001 more than fifty million hectares were planted worldwide with transgenic crops. The first generation of these crops has been altered in ways that improve the efficiency of crop production by modifying the tolerance of plants to herbicides and insect pests. Broad-spectrum herbicides are able to kill almost all plants. A prerequisite for using chemicals to control weeds in a crop is that the crop itself must be resistant to the herbicide. Genetic engineering has been used to develop plants (specifically soybean, canola, corn, and cotton) with resistance to two broad-spectrum herbicides, glyphosate and glufosinate, which are sold under the trademarks Roundup and Liberty, respectively. Glyphosate-tolerant soybeans have been adopted rapidly in some countries, notably the United States and Argentina, and accounted for approximately 46 percent of the soybean acreage worldwide in 2001. Herbicide use has not declined in these crops but the specific herbicides that are used have changed.

Insect pests can damage crops during the growing season and also after harvest. A variety of methods, including cultural practices and insecticides, are used to control insect damage. Genetic engineering has provided novel approaches to this problem. The bacterium Bacillus thuringiensis (Bt) produces proteins that are toxic to some types of insects, and Bt spores have been used as insecticides for decades. Genes encoding Bt toxin proteins have been isolated, modified so they function in plants, and transferred into crop plants including corn, potato, and cotton. These engineered Bt crops are more resistant to such insects as the European corn borer, Colorado potato beetle, and cotton bollworm than are their nonengineered counterparts. The introduction of Bt cotton has resulted in reduced use of insecticides on this crop in some regions of the United States. Growers of Bt crops are required to plant a portion of their acreage with varieties that do not carry the Bt gene, in an effort to delay the development of insect populations with resistance to Bt toxins.

The Flavr Savr tomato, developed in the 1980s by Calgene, a biotechnology company in California, was the first food produced from a genetically engineered plant. These tomatoes ripened more slowly and had an extended shelf life. However, for a number of reasons—including production problems and consumer skepticism—this product was not a commercial success and was withdrawn in 1996, after less than three years on the market. Melons and raspberries have also been engineered to have delayed ripening but have not been produced commercially. Transgenic papayas with resistance to ring spot virus also have been developed. These were grown successfully in Hawaii, where the papaya industry was devastated by this debilitating disease. A similar approach was used to produce virus-resistant summer squash and against other viruses affecting a wide variety of foodstuffs.

The first generation of transgenic crops for the most part were designed to improve the efficiency of crop production, an ongoing objective for genetic engineers. Additionally, the techniques of genetic engineering can be used to alter the nutritional composition of foods. The transfer into rice of three genes that function to produce beta-carotene in the seed resulted in "golden rice." Once consumed, beta-carotene can be converted to vitamin A, the degree of this conversion being dependent upon a number of factors that relate to the source of the beta-carotene, the diet, and the individual consumer. In less-developed countries, vitamin A deficiency is widespread among those with a restricted diet, and is responsible for increased mortality and blindness in children. Although the efficacy of transgenic rice in reducing disease has not been established, it demonstrates the potential use of genetic engineering for nutritional enhancement in many crops. Other applications of genetic engineering of animal and human foods include removing allergens from foods such as peanuts, increasing the level of essential vitamins and nutrients in foods, and producing foods possessed of vaccines and other beneficial compounds.

Genetically engineered microbes also are used to produce proteins for food processing. Chymosin (or rennin), an enzyme used in cheese production, traditionally is obtained from the stomach of veal calves. However, the gene encoding this enzyme was transferred into microbes, and the enzyme now can be produced in bulk by purifying it from large microbe cultures. Chymosin prepared from transgenic microbes has more predictable properties than the animal product and is used to produce more than fifty percent of hard cheeses in the United States. Other enzymes used in food processing are produced by similar methods. For example, bovine growth hormone (BGH) is produced in large quantities from transgenic microbes and is given to cows to increase milk production.

The History of Genetic Engineering

Genetic engineering owes its existence to the developments in molecular genetics, virology, and cytology that culminated in the determination of the structure of DNA by James Watson and Francis Crick in 1953. Building on research involving bacteriophages (a bacterial virus), Joshua Lederberg, a geneticist at the University of Wisconsin, found that bacteria can transfer genetic information through plasmids, small mobile pieces of DNA that exist independent of the chromosomes. In the 1950s, Lederberg pioneered the earliest techniques in genetic engineering, shuffling genetic material between bacterial cells. After the identification of restriction enzymes capable of "cutting" DNA in specific locations in 1968, scientists were able to insert foreign DNA directly into bacterial cells. The discovery that the foreign DNA would naturally bond with the host DNA, made it possible to splice together genes from multiple organisms, the technique used in recombinant DNA engineering. Although highly complicated, rDNA engineering can be simply explained: genetic material from the donor source is isolated and "cut" using a restriction enzyme and then recombined or "pasted" into the genetic material of the receiver. By 1971, advanced transplantation techniques had been developed and rDNA techniques using the restriction enzyme EcoRi were operable the following year, leading to the first experiments in genetic engineering.
In 1973, Stanford biochemist Stanley Cohen under-took one of the first rDNA experiments, inserting a piece of bacterial DNA into Escherichia coli (E. coli), a bacterium found in the human intestine. However, the research soon became controversial, particularly when American molecular biologist Paul Berg designed an experiment to insert DNA from simian virus #40 (sv40)—a known cancer-causing agent—into E. coli. As word of the daring procedure spread, the public was captivated and fearful, afraid that a genetically engineered virus, inured to antibiotics and carried in a common bacterium, could escape and cause an epidemic. Hoping to diffuse fears of a potential biohazard and maintain control of their research, over one hundred and fifty molecular biologists and related specialists met at the Asilomar Conference Center in Monterey, California, in late February 1975. The conference represented an extraordinary moment in the history of science, as the research community, recognizing its social responsibility, officially adopted a moratorium until appropriately safe procedures and guidelines could be developed. The conference ultimately resulted in the "National Institutes of Health Guidelines for Research Involving rDNA Molecules" and an ongoing National Institute of Health rDNA Advisory Committee (RAC)founded in 1974.

Yet the guidelines only increased public concern over genetic engineering. Critics charged that attempts to splice genes together from different organisms were akin to "playing God" and could result in dangerous and immoral hybrids. Adopting the literary example of "Dr. Frankenstein's monster" as an appropriate symbol of misguided science, opponents of rDNA engineering converged on research laboratories and public meetings. An attempt to build a recombinant laboratory at Harvard University set off such a firestorm that local politicians created a review board to assess potential risks, eventually requiring more stringent controls than those set by the NIH. By 1977, protests of rDNA facilities had spread to other campuses—the University of California San Diego, the University of Wisconsin, the University of Michigan, and the University of Indiana—while the state legislatures of New York, New Jersey, and California held public hearings. However, it was the resolution of an old court case and the introduction of a new form of rDNA engineering that ultimately created the greatest controversy.

In a monumental decision handed down on 16 June 1980, the United States Supreme Court held in Diamond v. Chakrabarty that man-made life forms were subject to patent laws and protection. The decision resolved a longstanding issue on patents and organic material, as the case dated to 1972, when Ananda Chakrabarty, a researcher at General Electric, applied for a patent on a form of Pseudomonas bacteria bred (but not genetically engineered)to digest oil slicks. By a narrow five to four margin the court construed the Patent Act, originally drafted by Thomas Jefferson, so as to include all products of human invention, relying on a 1952 Senate report that recognized as patentable "anything under the sun that is made by man." More than any other single event, the ruling galvanized many mainstream religious communities and environmental groups, eventually resulting in a letter of protest to President Carter and an indepth review by the President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research (1980–1983). The commission's report, issued in 1982 and entitled Splicing Life: The Social and Ethical Issues of Genetic Engineering with Human Beings, emphasized the importance of rDNA engineering to biomedical progress and American industries, arguing that it was best that the research be conducted under the auspices of government regulation and control. However, while the study resolved anxiety over rDNA engineering and patenting, proponents of genetic engineering still had to address concerns over the development of "germ-line" engineering, a controversial procedure that allowed scientists to literally create new strains of organisms.

Germ-line engineering differs from rDNA engineering in that the donor genes are inserted into a "germ," or reproductive cell, thereby permanently altering the genetic makeup of the organism's descendants. For example, in 1982, Ralph Brinster of the University of Pennsylvania Veterinary School inserted the gene that produces rat growth hormone into mouse embryos. The resulting strain of mice, dubbed "super mice" by the press, expressed the gene and thus grew into a substantially larger and more powerful new breed of mouse. Critics of germ-line engineering quickly denounced the technique as immoral and argued it was a form of "anthropomorphic Lamarckism."
Jean-Baptiste de Lamarck, a nineteenth-century French naturalist, had proposed that traits acquired during an organism's lifetime were passed on to its progeny—an idea refuted by Darwinian evolutionary theory. Yet, in germ-line engineering, traits acquired during the organism's lifetime are passed on, but only those traits deemed necessary or desirous by man. Environmental groups also denounced germ-line engineering because of "biosafety" concerns, fearing that genetically engineered species, which would possess a distinct advantage over nonengineered species, could upset the globe's finely tuned ecological systems. However, because most politicians, scientists, and manufacturers believed the potential benefits from rDNA and germ-line engineering outweighed its potential dangers, the protests were overshadowed by the development of a biotechnology industry based on genetic engineering.

Animal cells and plant cells

Animal cells

In contrast to the wide variety of plasmid and phage vectors available for cloning in prokaryotic cells, relatively few vectors are available for introducing foreign genes into animal cells. The most commonly used are derived from simian virus 40 (SV40). Normal SV40 cannot be used as a vector, since there is a physical limit to the amount of DNA that can be packaged into the virus capsid, and the addition of foreign DNA would generate a DNA molecule too large to be packaged. However, SV40 mutants lacking portions of the genome can be propagated in mixed infections in which a “helper” virus supplies the missing function.

Plant cells

Two systems for the delivery and integration of foreign genes into the plant genome are the Ti plasmid of the soil bacterium Agrobacterium and the DNA plant virion cauliflower mosaic virus. The Ti plasmid is a natural gene transfer vector carried by A. tumefaciens, a pathogenic bacterium that causes crown gall tumor formation in dicotyledonous plants. A T-DNA segment present in the Ti plasmid becomes stably integrated into the plant cell genome during infection. This property of the Ti plasmid has been exploited to show that DNA segments inserted in the T-DNA region can be cotransferred to plant DNA.

Applications

Recombinant DNA technology has permitted the isolation and detailed structural analysis of a large number of prokaryotic and eukaryotic genes. This contribution is especially significant in the eukaryotes because of their large genomes. The methods outlined above provide a means of fractionating and isolating individual genes, since each clone contains a single sequence or a few DNA sequences from a very large genome. Isolation of a particular sequence of interest has been facilitated by the ability to generate a large number of clones and to screen them with the appropriate “probe” (radioactively labeled RNA or DNA) molecules.

Genetic engineering techniques provide pure DNAs in amounts sufficient for mapping, sequencing, and direct structural analyses. Furthermore, gene structure-function relationships can be studied by reintroducing the cloned gene into a eukaryotic nucleus and assaying for transcriptional and translational activities. The DNA sequences can be altered by mutagenesis before their reintroduction in order to define precise functional regions.

Genetic engineering methodology has provided means for the large-scale production of polypeptides and proteins. It is now possible to produce a wide variety of foreign proteins in E. coli. These range from enzymes useful in molecular biology to a vast range of polypeptides with potential human therapeutic applications, such as insulin, interferon, growth hormone, immunoglobins, and enzymes involved in the dynamics of blood coagulation.

Cloning vectors

There is a large variety of potential vectors for cloned genes. The vectors differ in different classes of organisms.

Prokaryotes and lower eukaryotes

Three types of vectors have been used in these organisms: plasmids, bacteriophages, and cosmids. Plasmids are extrachromosomal DNA sequences that are stably inherited. Escherichia coli and its plasmids constitute the most versatile type of host-vector system known for DNA cloning. Several natural plasmids, such as ColE1, have been used as cloning vehicles in E. coli. In addition, a variety of derivatives of natural plasmids have been constructed by combining DNA segments and desirable qualities of older cloning vehicles. The most versatile and widely used of these plasmids is pBR322. Transformation in yeast has been demonstrated using a number of plasmids, including vectors derived from the naturally occurring 2μ plasmid of yeast.

Bacteriophage lambda is a virus of E. coli. Several lambda-derived vectors have been developed for cloning in E. coli, and for the isolation of particular genes from eukaryotic genomes. These lambda derivatives have several advantages over plasmids: (1) Thousands of recombinant phage plaques can easily be screened for a particular DNA sequence on a single petri dish by molecular hybridization. (2) Packaging of recombinant DNA in laboratory cultures provides a very efficient means of DNA uptake by the bacteria. (3) Thousands of independently packaged recombinant phages can be easily replicated and stored in a single solution as a “library” of genomic sequences.
Plasmids have also been constructed that contain the phage cos DNA site, required for packaging into the phage particles, and ColE1 DNA segments, required for plasmid replication. These plasmids have been termed cosmids. The recombinant cosmid DNA is injected into a host and circularizes like phage DNA but replicates as a plasmid. Transformed cells are selected on the basis of a vector drug resistance marker.

Joining DNA molecules

Once the proper DNA fragments have been obtained, they must be joined. When cleavage with a restriction endonuclease creates cohesive ends, these can be annealed with a similarly cleaved DNA from another source, including a vector molecule. When such molecules associate, the joint has nicks a few base pairs apart in opposite strands. The enzyme DNA ligase can then repair these nicks to form an intact, duplex recombinant molecule, which can be used for transformation and the subsequent selection of cells containing the recombinant molecule. Cohesive ends can also be created by the addition of synthetic DNA linkers to blunt-ended DNA molecules.

Another method for joining DNA molecules involves the addition of homopolymer extensions to different DNA populations followed by an annealing of complementary homopolymer sequences. For example, short nucleotide sequences of pure adenine can be added to the 3′ ends of one population of DNA molecules and short thymine blocks to the 3′ ends of another population. The two types of molecules can then anneal to form mixed dimeric circles that can be used directly for transformation.

The enzyme T4 DNA ligase carries out the intermolecular joining of DNA substrates at completely base-paired ends; such blunt ends can be produced by cleavage with a restriction enzyme or by mechanical shearing followed by enzyme treatment.

Transformation
The desired DNA sequence, once attached to a DNA vector, must be transferred to a suitable host. Transformation is defined as the introduction of foreign DNA into a recipient cell. Transformation of a cell with DNA from a virus is usually referred to as transferring.

Transformation in any organism involves (1) a method that allows the introduction of DNA into the cell and (2) the stable integration of DNA into a chromosome, or maintenance of the DNA as a self-replicating entity. See also Transformation (bacteria).

Escherichia coli is usually the host of choice for cloning experiments, and transformation of E. coli is an essential step in these experiments. Escherichia coli treated with calcium chloride are able to take up DNA from bacteriophage lambda as well as plasmid DNA. Calcium chloride is thought to effect some structural alterations in the bacterial cell wall. An efficient method for transformation in Bacillus species involves polyethylene glycol-induced DNA uptake in bacterial protoplasts and subsequent regeneration of the bacterial cell wall. Actinomycetes can be similarly transformed. Transformation can also be achieved by first entrapping the DNA with liposomes followed by their fusion with the host cell membrane. Similar transformation methods have been developed for lower eukaryotes such as the yeast Saccharomyces cerevisiae and the filamentous fungus Neurospora crassa.

Isolation of passenger DNA

Passenger DNA may be isolated in a number of ways; the most common of these involves DNA restriction. Restriction endonucleases make possible the cleavage of high-molecular-weight DNA. Although three different classes of these enzymes have been described, only type II restriction endonucleases have been used extensively in the manipulation of DNA. Type II restriction endonucleases are DNAases that recognize specific short nucleotide sequences (usually 4 to 6 base pairs in length), and then cleave both strands of the DNA duplex, generating discrete DNA fragments of defined length and sequence. A number of restriction enzymes make staggered cuts in the two DNA strands, generating single-stranded termini. See also Restriction enzyme.

The various fragments generated when a specific DNA is cut by a restriction enzyme can be easily resolved as bands of distinct molecular weights by agarose gel electrophoresis. Specific sequences of these bands can be identified by a technique known as Southern blotting. In this technique, DNA restriction fragments resolved on a gel are denatured and blotted onto a nitrocellulose filter. The filter is incubated together with a radioactively labeled DNA or RNA probe specific for the gene under study. The labeled probe hybridizes to its complement in the restricted DNA, and the regions of hybridization are detected autoradiographically. Fragments of interest can then be eluted out of these gels and used for cloning. Purification of particular DNA segments prior to cloning reduces the number of recombinant that must later be screened. See also Electrophoresis.

Another method that has been used to generate small DNA fragments is mechanical shearing. Intense personification of high-molecular-weight DNA with ultrasound, or high-speed stirring in a blender, can both be used to produce DNA fragments of a certain size range. Shearing results in random breakage of DNA, producing termini consisting of short, single-stranded regions. Other sources include DNA complementary to poly(A) RNA, or cDNA, which is synthesized in the test tube, and short oligonucleotides that are synthesized chemically.

Cloning of cells

A clone is a cell, group of cells, or organism that contains genetic information identical to that of the parent cell or organism. It is a form of asexual reproduction (see Reproduction), and as such it is not as new as it seems; what is new, however, is humans' ability to manipulate cloning at the genetic level. The first clones produced by humans as long as 2,000 years ago were plants developed from grafts and stem cuttings. By cloning—a process that calls into play complex laboratory techniques and the use of DNA replication—people usually mean a relatively recent scientific advance. Among these techniques is the ability to isolate and copy (that is, to clone) individual genes that direct an organism's development.

The Promise of Cloning
The cloning of specific genes can provide large numbers of copies of that gene for use in genetic and taxonomic research as well as in the practical areas of medicine and farming. In the latter field, the goal is to clone plants with specific traits that make them superior to naturally occurring organisms. For example, in 1985 scientists conducted field tests using clones of plants whose genes had been altered in the laboratory to generate resistance to insects, viruses, and bacteria. New strains of plants resulting from cloning could produce crops that can grow in poor soil or even underwater and fruits and vegetables with improved nutritional qualities and longer shelf lives. A cloning technique known as twinning could induce livestock to give birth to twins or even triplets, and on the environmental front cloning might help save endangered species from extinction.

In the realm of medicine and health, cloning has been used to make vaccines and hormones. It has become possible, by combining two different kinds of cells (such as mouse and human cancer cells), to produce large quantities of specific antibodies, via the immune system, to fight off disease. When injected into the bloodstream, these cloned antibodies seek out and attack disease-causing cells anywhere in the body. By attaching a tracer element to the cloned antibodies, scientists can locate hidden cancers, and by attaching specific cancer-fighting drugs, the treatment dose can be transported directly to the cancer cells.

Experiments in Cloning
The modern era of laboratory cloning began in 1958 when the British plant physiologist F. C. Steward (1904-1993) cloned carrot plants from mature single cells placed in a nutrient culture containing hormones. The first cloning of animal cells took place in 1964, when the British molecular biologist John B. Gurdon (1933-1989) took nuclei from intestinal cells of toad tadpoles and injected them into unfertilized eggs. The cell nuclei in the eggs had been destroyed with ultra-violet light, but when the eggs were incubated, Gurdon found that 1-2% of the eggs developed into fertile, adult toads.

The first successful cloning of mammals occurred nearly 20 years later, when scientists in Switzerland and the United States successfully cloned mice using a method similar to Gurdon's approach. Their method required one extra step, however: after taking the nuclei from the embryos of one type of mouse, they transferred them into the embryos of another type of mouse. The latter served as a surrogate, or replacement, mother. The cloning of cattle livestock was tried first in 1988, when embryos from prize cows were transplanted to unfertilized cow eggs whose own nuclei had been removed. An even greater breakthrough transpired on February 24, 1997, with the birth of a lamb named Dolly in Edinburgh, Scotland. Dolly was no ordinary sheep: she was the first mammal born from the cloning of an adult cell. Thus, she had been produced by asexual reproduction in the form of genetically engineered cloning rather than by anything resembling a normal process. Nonetheless, she proved her own ability to reproduce the old-fashioned way when, on April 23, 1998, she gave birth to a daughter named Bonnie.

DNA Big real life application

Ever since the breakthrough discoveries of Watson, Crick, and others in the 1950s made genetic engineering a possibility, the new field has promised increasingly bigger payoffs. These payoffs take the form of improvements to human life and profits to those who facilitate those improvements. The possible applications of genetic engineering are virtually limitless—as are the profits to be made from genetic engineering as a business. As early as the 1970s, entrepreneurs (independent businesspeople) recognized the commercial potential of genetically engineered products, which promised to revolutionize life, technology, and commerce as computers also were doing. Thus was born one of the great buzzwords of the late twentieth century: biotechnology, or the use of genetic engineering for commercial purposes.

Several early biotechnology firms were founded by scientists involved in fundamental research: Boyer, for example, teamed up with the venture capitalist Robert Swanson in 1976 to form Genentech (Genetic Engineering Technology). Other pioneering companies, including Cetus, Biogen, and Genex, likewise were founded through the collaboration of scientists and businesspeople. Today biotechnology promises a revolution in numerous areas, such as agriculture. Recombinant DNA techniques enable scientists to produce plants that are resistant to freezing temperatures, that will take longer to ripen, that will develop their own resistance to pests, and so on. By 1988 scientists had tested more than two dozen kinds of plants engineered to have special properties such as these. Yet no field of biotechnology and genetic engineering is as significant as the applications to health and the cures for diseases.

Medicines and Cures
The use of rDNA allows scientists to produce many products that were previously available only in limited quantities: for example, insulin, which we referred to earlier. Until the 1980s the only source of insulin for people with diabetes came from animals slaughtered for meat and other purposes. The supply was never high enough to meet demand, and this drove up prices. Then, in 1982, the U.S. Food and Drug Administration (FDA) approved the sale of insulin produced by genetically altered organisms—the first such product to become available. Since 1982 several additional products, such as human growth hormone, have been made with rDNA techniques.

One of the most exciting potential applications of genetic engineering is the treatment of genetic disorders, which are discussed in Heredity, through the use of gene therapy. Among the more than 3,000 such disorders, quite a few of which are quite serious or even fatal, many are the result of relatively minor errors in DNA sequencing. Genetic engineering offers the potential to provide individuals with correct copies of a gene, which could make possible a cure for that condition. In the 1980s scientists began clinical trials of a procedure known as human gene therapy to replace defective genes. The technique, still very much in the developmental stage, offers the hope of cures for diseases that medicine has long been powerless to combat.

In 2001 scientists at the Weizmann Institute in Israel brought together two of the most exciting fields of research, biotechnology and computers, to produce the DNA-processing nanocomputer. It is an actual computer, but it is so small that a trillion of them would fit in a test tube. It consists of DNA and DNA-processing enzymes, both dissolved in liquid; thus its input, output, and software are all in the form of DNA molecules. The purpose of the nanocomputer is to analyze DNA, detecting abnormalities in the human body and creating remedies for them.

Principles of Genetic Engineering

Just as DNA is at the core of studies in genetics, recombinant DNA (rDNA)—that is, DNA that has been genetically altered through a process known as gene splicing—is the focal point of genetic engineering. In gene splicing, a DNA strand is cut in half lengthwise and joined with a strand from another organism or perhaps even another species. Use of gene splicing makes possible two other highly significant techniques. Gene transfer, or incorporation of new DNA into an organism's cells, usually is carried out with the help of a microorganism that serves as a vector, or carrier. Gene therapy is the introduction of normal or genetically altered genes to cells, generally to replace defective genes involved in genetic disorders.

DNA also can be cut into shorter fragments through the use of restriction enzymes. (An enzyme is a type of protein that speeds up chemical reactions.) The ends of these fragments have an affinity for complementary ends on other DNA fragments and will seek those out in the target DNA. By looking at the size of the fragment created by a restriction enzyme, investigators can determine whether the gene has the proper genetic code. This technique has been used to analyze genetic structures in fetal cells and to diagnose certain blood disorders, such as sickle cell anemia.

Gene Transfer
Suppose that a particular base-pair sequence carries the instruction "make insulin"; if a way could be found to insert that base sequence into the DNA of bacteria, for example, those bacteria would be capable of manufacturing insulin. This, in turn, would greatly improve the lives of people with type 1 diabetes, who depend on insulin shots to aid their bodies in processing blood sugar. (See Non-infectious Diseases for more about diabetes.)

Although the concept of gene transfer is relatively simple, its execution presents considerable technical obstacles. The first person to surmount these obstacles was the American biochemist Paul Berg (1926-), often referred to as the "father of genetic engineering." In 1973 Berg developed a method for joining the DNA from two different organisms, a monkey virus known as SV40 and a virus called lambda phage. Although the accomplishment was clearly a breakthrough, Berg's method was difficult. Then, later that year, the American biochemists Stanley Cohen (1922-) at Stanford University, and Herbert Boyer (1936-) at the University of California at San Francisco discovered an enzyme that greatly increased the efficiency of the Berg procedure. The gene-transfer technique developed by Berg, Boyer, and Cohen formed the basis for much of the ensuing progress in genetic engineering.