DNA ChemicaI Structure, Model of DNA strand And Computer Model of DNA

DNA Structure. one DNA molecule exists as a double-stranded  structure. Each of DNA strand is connected  by nucleotide  to form double chain structure  that is arranged like  twisted  ladder. The DNA structure is also known as double helix.

Double  helix of DNA structure.  (a) Model of DNA strand. (b) computer model  of DNA,  and  (c) DNA  chemicaI  structure.

According  to double helix DNA structure,  each nucleotide consists of three units, one molecule of deoxyribopentose  sugar' one group of phosphate, and one of four nitrogen base types. The four types of nitrogen base are purine group, which are adenine (A) and guanine (G); and pyrimidine  group,  thymine  (T) and cytosine (C).

Nucleotide  is buitt  by sugar,  phosphate, and base molecules.

Nucleotide on one DNA strand has specific bond with nucleotide  on its pair. Nucleotide containing adenine (A) always pairs with nucleotide containing thymine  (T), and  the one containing cytosine (C) always pairs with  that containing  guanine (G). Moreover, each pair of nitrogen base is matched through  hydrogen bond which is a weak chemical bond. The pair of nitrogen base guanine  (G) and cytosine  (C) is connected  by three hydrogen molecules,  while pair of nitrogen base  thymine  (T) and adenine (A) is connected  by two hydrogen molecules.

Four types  of nitrogen base.  (a) Chemical  structure  of nitrogen base and  (b) pair model of purine  and pyrimidine.

Double helix model of DNA structure was  first stated in 1953 by James D-Watson (an American biochemist)  and Francis  II.C. Crick (a British biophysics).  In 1962, they got Nobel Prize for modern biology. Double helix Structure of DNA discovered by them is considered to be able to explain protein synthesis, DNA  replication,  and mutation

source: Essential biology, 2006.

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