DNA Structure and Function

DNA Structure and Discovery

  • Base pairs are specific and predictable.

  • X-ray diffraction provided the first photograph of DNA, produced by Rosalind Franklin (Photo 51).

  • Watson and Crick developed a three-dimensional model of DNA.

DNA Model Features

  • Sugar-phosphate backbone with two antiparallel strands.

  • Antiparallel strands run in opposite directions (5' to 3' and 3' to 5').

  • Complementary base pairing: Adenine (A) with Thymine (T), Guanine (G) with Cytosine (C).

Importance of Base Pairing

  • Base pairs are crucial for genetic information storage and DNA replication.

  • Published model in 1953 by Watson and Crick.

Nucleotides and Bases

  • Four nucleotide bases in DNA: A, T, G, C.

  • Two categories: Purines (A, G - double ring) and Pyrimidines (C, T - single ring).

  • Purines are larger due to their structure.

  • Bases enable complementary base pairing and maintain uniform helix width.

Genetic Information

  • Approximately 3 billion base pairs encode for 20,000 genes in the human genome.

  • Some genes are identical across individuals, important for DNA analysis.

RNA vs DNA

  • RNA includes bases A, C, G, U (Uracil replaces Thymine).

  • Base pairing for RNA: A with U, C with G.

  • Understanding base pairing rules is crucial for transcription and analysis.