DNA Replication Ch 12-2

I. Chromosomes A. Wound up DNA 1. Prokaryotes: a single ring of DNA in the cytoplasm [Ex: E.coli has 4,639,221 base pairs (= 1.6mm long)]

2. Eukaryotes: Multiple chromosomes in the nucleus a) human cells contain 46 strands of DNA that stretch out to 1 meter.

B. Chromosome Stucture 1. Chromosomes contain DNA & proteins a) DNA coil around Histones. b) Histones with DNA coil up to make Nucleosomes. c) allows a large amount of DNA to fit into the microscopic space of the nucleus

II. DNA Replication A. Makes a copy of DNA 1. Occurs during Interphase (s-phase) of the cell cycle 2. Forms sister chromatids.

Replication of DNA

B. Steps of Replication: 1. DNA must unwind and unzip: a)Helicase: (an enzyme) breaks hydrogen bonds between base pairs causing the double helix to unwind and unzip b) the one double stranded DNA becomes 2 single strands of DNA

2. Two New Strands are Made: a) DNA Polymerase: (an enzyme) matches a nucleotide to its complimentary base pair on the single strand of DNA b) Base pairing enables existing DNA strand to serve as template for new complementary strands

c) Hydrogen bonds are reformed between the original base and the new nucleotide (recreating the steps of the ladder) d) New bonds between sugars and phosphates are created down the new backbone. (recreating the rails)

Replication of DNA

3. The end result: a) 2 new double strands of DNA b) Each DNA molecule has one original parent strand and a new complimentary strand.