Lecture 4
Nucleic acids (continued)
Pyrimidines: Cytosine, Thymine, Uracil. Single ring.
Purines: Adenine, Guanine. Double ring.
Polymer can be of two types: DNA, deoxyribonucleic acid, chemically more stable; RNA, ri-
bonucleic acid, chemically less stable.
DNA: A,G, C, T. RNA: A, G, C, U
One polymer (5' to 3') is called a strand or chain
DNA: typically double stranded and double chained (ds). RNA: typically single chained with
double-stranded portions due to intrastrand base-pairing
dsDNA: the two strands associate through H-bonds formed between bases
•
The H-bonds are formed between a pyrimidine and a purine: two in A=T pair, three in C=
G
pair
•
The H-bonds involve N---H and O---H interactions provided by atoms that are positioned on
the distal edge of each base (see book drawing)
•
The paired strands are in antiparallel: one 5' to 3', the other 3' to 5'
•
The strands wind to form a right-winded helix: the double helix
Origin of life
Consider the following:
•
organisms are formed of the molecules that we described
•
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- Spring '09
- LUCACOMAI
- DNA, RNA, Amino Acids, Nucleic Acids, intrastrand base-pairing dsDNA, Harold Urey experiment, undersea thermal vents
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