DNA
structure
DNA is a double (double stranded) helix, composed of four nucleotides,
Adenine (A), Guanine, G), Thymine (T) and Cytosine (C)
•
Adenine and
Guanine are Purines
-
they are larger
and have a double ring
•
Thymine and
Cytosine are Pyrmidines
-
they are
smaller and have a single ring .
•
The nucleotides
have three components, a pentose sugar, an amino base (the A, T, C, G), and a
phosphate group
•
The Nucleotides
are arranged in an anti-parallel double helix with Adenine
pairing with Thymine and Guanine pairing with Cytosine via hydrogen bonds
•
A purine always
pairs with a pyrmidine (A-T has two H-bonds, G-C has three H-bonds)
•
One strand runs
5' to 3' while the other runs 3' to 5'
Base Pairs
Within the DNA double helix, A forms 2 hydrogen bonds with T on the
opposite strand, and G forms 3 hyrdorgen bonds with C on the opposite strand.
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