Strand Of The Dna example essay topic

DNA is a term that has been used in science as well as in many parts of daily life. The general public knows that DNA is a part of our bodies but they may wonder what exactly is DNA? DNA is a term used for acid and its the genetic material of all organisms, it is the molecule of life and it determines all of our physical characteristics. DNA is present in every single form of life.

More than 50 years after the science of genetics was established and the patterns of inheritance were clarified, the largest questions remained unanswered: How are the chromosomes and their genes copied exactly from cell to cell, and how do they direct the structure and behavior of living things? Two American geneticists, George Wells Beadle and Edward Lawrie Tatum, provided one of the first important clues in the early 1940's. Working with the fungi Neurospora and Penicillium, they found that "genes direct the formation of enzymes through the units of which they are composed". (Annas) Each unit, a polypeptide is produced by a specific gene.

This establish the field of molecular genetics. The fact that chromosomes were almost entirely composed of two kinds of chemical substances, protein and nucleic acids, had long been known. In 1944, however, the Canadian bacteriologist Oswald Theodore Avery showed that (DNA) performed this role. He extracted DNA from one strain of bacteria and introduced it into another strain.

The second strain not only acquired characteristics of the first but passed them on to the next generation. Each nucleotide consists of a phosphate, a sugar known as deoxyribose, and any one of four nitrogen-containing bases. The four nitrogen bases are adenine (A), thymine (T), guanine (G), and cytosine (C). In 1953 James Dewey Watson of the United States and Francis Harry Crick of England worked out the structure of DNA. In 1962, both men earned the Nobel Prize in physiology for their discovery. This knowledge provided understanding how hereditary information is copied.

Watson and Crick found that the DNA molecule is composed of two long strands in the form of a double helix, resembling a long, spiral ladder. The strands, or sides of the ladder, are made up of alternating phosphate and sugar molecules. The nitrogen bases, joining in pairs, act as the rungs. Each base is attached to a sugar molecule and is linked by a hydrogen bond to a base on the opposite strand. Adenine always binds to thymine, and guanine always binds to cytosine. "To make a new, identical copy of the DNA molecule, the two strands unwind and separate at the bases which are weakly bound; with more nucleotides available in the cell, new complementary bases can link with each separated strand, and two double".

(Caldwell) Since the "backbone" of every chromosome is a single long, double-stranded molecule of DNA, the production of two identical double result in the production of two identical chromosomes. The DNA backbone is actually longer than the chromosome but is tightly coiled up within it. This packing is now known to be based on minute particles of protein known as, that can only be seen under the most powerful electron microscope. The DNA is wound around each to form a beaded structure. The structure is then further folded so that the beads associate in regular coils. Thus, the DNA has a "coiled-coil" configuration.

After the discoveries of Watson and Crick, the question that remained was how the DNA directs the formation of proteins, compounds central to all the processes of life. Proteins are not only the major components of most cell structures, they also control virtually all the chemical reactions that occur in living matter. The ability of a protein to act as part of a structure, or as an enzyme affecting the rate of a particular chemical reaction, depends on its molecular shape. This shape, in turn, depends on its composition.

Every protein is made up of one or more components called polypeptides, and each polypeptide is a chain of subunits called amino acids. Twenty different amino acids are found in polypeptides. The number, type, and order of amino acids ina chain ultimately determine the structure and function of the protein. Since proteins were shown to be products of genes, and each gene was shown to be composed of sections of DNA strands, scientists found that a genetic code must exist by which the order of the four nucleotide bases in the DNA could direct the sequence of amino acids in the formation of polypeptides.

Because only four different kinds of nucleotides occur in DNA, but 20 different kinds of amino acids occur in proteins, the genetic code could not be based on one nucleotide specifying one amino acid. Ten years after Watson and Crick reported the DNA structure, the genetic code was worked out and proved biologically. Its solution depended on a great deal of research involving another group of nucleic acids, the ribonucleic acids called RNA. The specification of a polypeptide by the DNA was found to take place indirectly, through an intermediate molecule known as messenger RNA, or mRNA.

Part of the DNA is from its chromosome packing, and the two strands become separated for some of their length. One of them serves as a template in which the m RNA is formed, with the aid of an enzyme called RNA polymerase. This process is very similar to the formation of a complementary strand of DNA during the division of the double helix, except that RNA contains uracil (U) instead of thymine as one of its four nucleotide bases, and the uracil, which is similar to thymine, joins with the adenine in the formation of complementary pairs. Thesis because thymine cannot travel outside of the nucleus. Thus, a sequence adenine-guanine-adenine-thymine-cytosine (AGATE) in the coding strand of the DNA produces a sequence uracil-cytosine-uracil-adenine-guanine (UCUAG) in the m RNA. Ribosomes are made up of protein and RNA.

A group of ribosomes linked by mRNA is called a poly ribosome, or poly some. As each ribosome passes along the mRNA molecule, it "reads" the code, which is the sequence of nucleotide bases on the mRNA. The reading, called translation, takes place by a third type of RNA molecule called transfer RNA (t RNA), which is produced on another segment of the DNA. On one side of the t RNA molecule is a triplet of nucleotides. On the other side is a region to which one specific amino acid can become attached with the aid of a specific enzyme. The triplet on each t RNA is complementary to one particular sequence of three nucleotides-the codon-on the m RNA strand.

Because of this complementary, the triplet is able to "recognize" the codon. For example, the sequence uracil-cytosine-uracil (UC) on the strand of mRNA attracts the triplet adenine-guanine-adenine (AGA) of the t RNA. The t RNA triplet is known as the anti codon. In bacteria, viruses, and blue-green algae, the chromosome lies free in the cytoplasm, and the process of translation may start even before the process of transcription is completed.

In higher organisms, however, the chromosomes are isolated in the nucleus and the ribosomes are contained only in the cytoplasm. Thus, translation of m RNA into protein can occur only after the m RNA has become detached from the DNA and has moved out of the nucleus. Scientists continue to study the DNA molecule with hopes of find the secrets that are hidden with in our own bodies. Their findings continue to aid us in cures and the prevention of many illnesses that years ago we couldn't solve.

Hopefully the research will soon pay off, with the cure for cancer or Alzheimer's Disease. DNA has also been very important in Forensic science where it is used to identify individuals who have committed a crime. More recently, DNA has been valuable in identifying those who were lost in the World Trade Center disaster. Genetic scientists working on what is known as the Human Genome Project have been able to map all of the sequences of the three billion nucleotide base pairs that make up the human genetic material. This will prove to be very important and will pave the way for many life changing discoveries. This fact has caused some controversy due to religious and moral matters because it gives man much power over the development of future generations.

Although this may be a concern I feel that there are many benefits in the ability we will have to do amazing things because of these recent discoveries..