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Scroll to unzip the double helix
DNA is a double helix of two antiparallel sugar-phosphate backbones connected by complementary base pairs. It twists once every 10 base pairs (3.4 nm).
A-T connected by 2 hydrogen bonds; G-C by 3. Chargaff's rule: A=T and G=C in amount. This complementarity enables faithful replication.
Segments of DNA coding for proteins. Contain promoters, exons (coding), introns (non-coding), and terminators. Humans have ~20,000 genes.
Semiconservative: each strand serves as template. DNA polymerase adds nucleotides at ~1,000 bases/second with 1 error per billion bases.
Changes in base sequence. Substitution (swap), insertion (add), deletion (remove). Can be silent, missense (wrong amino acid), or nonsense (premature stop).
3.2 billion base pairs, ~20,000 protein-coding genes. 99.9% identical between humans. If stretched out, DNA from one cell = 2 meters long.