MOLECULAR GENETICS REVIEW
Deoxyribonucleic acid is a polymer of nucleotide, Nucleotides have a 5-carbon sugar, a
phosphate group (phospho-diester bond) and a nitrogenous base (A,T,G,C ) (H-bond)
Purines 6-membered ring joined to a 5-membered ring (A,G)
Pyrimidines single 6-membered ring (C,T)
*A-T are double bonded, while G-C are triple bond (stronger)*
DNA consist of two antiparallel strands curled around in a double helix (like a spiral) 5’ to
3’ and 3’ to 5’
*The 5’ end is the one that stars with a phosphate, and the 3’ ends with a OH*
*The right handed helix turns CLOCKWISE*
Semiconservative model the daughter DNA molecule is made up of one parental strand and
one new strand (parental strand serves as a template)
Chromosome is 60% proteins (Histone is a protein that prevents DNA from tangling)
During interphase of cell division the DNA molecule duplicates itself. First step involves the
splitting of the double helix into its two halves. On the 3’ to 5’ strand new DNA is
replicated continuously towards the replication fork. On the 5’ to 3’ the replication is
discontinuous, away from the fork.
1. DNA Helicase- Uncoils the 2 strands by breaking H-bonds b/w nitrogen bases.
2. DNA Gyrase- Relieves tension in untwisted strands.
3. Single Stranded Binding Proteins (SSBPs) – Protein that keeps the two strands apart.