DNA

DNA is the abbreviation for the double helix molecule, deoxyribonucleic acid. It is a long chain polymer (polynucleotide) which is found is all living cells. Using its chemical patterns it directs the formation, growth, operations and reproduction of individual cells and thus of organs and of living organisms. The DNA molecule is very long and is like a spiral staircase or a double helix in structure. The structure of DNA was first discovered by James D. Watson and Francis H. C. Cricket in 1953. The discovered of the structure opened the way for detailed understanding of the chemistry of the DNA molecule and of genetics as well.

DNA molecules are composed of two polynucleotide strands wrapped around each other to form a double helix. They consist of two long nucleotides composed of a sugar molecule and a phosphate group bonded to a DNA base. This sequence is repeated numerous times to form genes and chromosomes. The legs of the DNA spiral staircase have major and minor groves. Other chemicals form the connecting steps. The whole molecule is composed of thousands of smaller chemical units called nucleotides which are bonded together to form polynucleotides.

Nucleotides are composed of a phosphate, a sugar (deoxyribose) and another compound which is called generally a base. The sugar is 2′-deoxyribose which has five carbon atoms. The carbon atoms in the sugar molecule are named 1′ (prime), 2′ and so forth. Hydrogen bonds between bases on the two DNA strands stabilize the double helix.

There are four types of bases: adenine, guanine, thymine, and cytosine. The adenine and guanine bases have two carbon-nitrogen rings and are purines. The thymine and cytosine bases have a single ring and are pyrimidine. The bases are attached to the 1′ carbon of the deoxyribose. It takes a sugar plus a base to make a nucleoside. Nucleotides have one, two, or three phosphate [Page 548]groups. These are attached to 5′-carbon atom of the sugar molecule.

The bases vary in the nucleotides, but the sugar and the phosphate are the same in all DNA nucleotides. Nucleotides may be individual molecules or they may be polymers of DNA or ribonucleic acid (RNA). It is the varying combinations of bases that create the power of the DNA molecule to replicate itself thus to grow new living cells. The nucleotides bonded as triphosphates of the four bases that are boned into DNA polynucleotide chains.

The base adenine is a heterocyclic aromatic organic compound. It is composed of a pyrimidine ring which is fused to an imidazole ring. There are two types of nitrogenous bases—purine and pyrimidines. Purines are the essential part of both deoxyribonucleotides (DNA) and ribonucleotides (RNA). In addition to its role in DNA and RNA adenine is an important part of many organic chemical reactions and processes. The reactions include protein synthesis and cellular respiration.

In earlier chemistry adenine was often identified as vitamin B4, but understanding has been modified. Adenine combines with two of the B vitamins—niacin and riboflavin. These form into essential cofactors. Some evolutionists have argued that adenine was synthesized from hydrogen cyanide (HCH) to begin the formation of life; however, this view is not universally held.

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