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Deoxyribonucleic acids (DNA) are polymers with molecular weights ranging from
6 to 16 million amu (atomic mass units).
The individual monomers, called
nucleotides, comprise of three basic units; (i) a phosphoric acid (phosphate)
group, (ii) a five carbon sugar (deoxyribose) and (iii) an organic base;
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The individual units join together to form
nucleotides, the diagram to the right is of a nucleotide based on ADENINE.
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These nucleotides then link together by reaction of the
phosphoric group of one nucleotide with the sugar unit of another
nucleotide as shown below;
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The single strands of DNA are wound together to form a
double helix, the two strands being held together by attractions between
the bases attached to the sugar-phosphate backbone.
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The organic bases form complementary pairs;
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adenine (A) is always
matched with thymine (T) |
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cytosine
(C) is always matched with guanine (G) |
The key attractions are the hydrogen bonds between the N, H
and O atoms on the bases. |
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Although the pairs of bases have to remain the same, A with T and
C with G, there is no restriction on the sequence of resulting base
pairs on the strands; |
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Follow this link to read an electronic
"reprint" of Watson and Crick's original paper in Nature
proposing a structure for DNA;
J.D. Watson and
F.H.C.Crick, Nature, Vol 171,
page 573, 1953
[ Up ] [ DNA Structure ] [ Function of DNA ] [ RFLP DNA Typing ]
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