DNA! spooled gene chromosomes chromatin double helix

1953 Wilkins Franklin Watson Crick

• sugar-base-phosphate monomer • polymer • linear • bases evenly spaced

• S/P/B monomer • polymer • linear • double molecule • bases evenly spaced • bases stacked • base ratio: A=T C=G • P on outside

Nucleotides are the monomer of nucleic acids This component varies

nucleotides creates a nucleic acid, a polymer The chain of nucleotides creates a nucleic acid, a polymer

The two helices are anti-parallel sugar covalent bond nitrogen bases phosphate H-bond between them N-base The two helices are anti-parallel constructed, read in opposite directions

DNA has 4 nucleotides purines pyrimidines

The base pair rule makes the two helices complementary Adenine bonds to Thymine H-bonds Cytosine bonds to Guanine

DNA is replicated when cells reproduce (mitosis, meiosis) • each old strand acts as a template for a new one • the two stands each contain half of the original Thus replication is semi-conservative

mistakes happen! aka mutations

‘spelling’ error - point mutation extra base inserted, Possibilities: ‘spelling’ error - point mutation extra base inserted, one base skipped (deleted) frameshift effect DNA sequence is ‘read’ in sets of 3 nucleotides, called codons point mutations change one codon; frameshift changes all codons past the error ‘spelling’ error deletion