DNA Replication

Biology 102b

Replication Fork

y-shaped region where new DNA strands are elongating

Helicase

Enzymes that untwist the double helix at the replication forks

Single-strand binding proteins

bind to and stabilize single-stranded DNA

Topoisomerase

corrects “overwinding” or coiling ahead of replication forks by breaking, swiveling, and rejoining DNA strandsenzymes that relieve torsional strain during DNA replication

DNA Polymerase definition

Can only add nucleotides to an existing 3’ end, not start new synthesis; catalyze elongation of new DNA at a replication fork

Phosphate group is attached to the

5’ end

RNA Primer

Initial nucleotide strand

DNA Polymerase requirements

primer and DNA template strand

Double Helix Structure

Antiparallel

Leading Strand

DNA polymerase synthesizes this continuously along one template strand of DNA toward the replication fork

Okazaki Fragments

located on lagging strand (3’-5’ wrong direction), DNA polymerase makes non-continuous DNA strands, making gaps called this

DNA Ligase

fix okazaki fragments (that can cause cancer if unfixed)

DNA pol III

Using parental DNA as a template synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand

DNA Pol I

removes RNA nucleotides of primer from 5’ end and replaces them w/ DNA nucleotides

Primase

synthesizes an RNA primer at 5’ end of leading strand and 5’ end of each Okazaki fragment of each lagging strand

Mismatch repair

DNA, rapid enzymes correct errors in base pairing

Nucleotide excision repair

a nuclease cuts out and replaces damaged stretched of DNA

Telomeres

special nucleotide sequences at ends of eukaryotic chromosomal DNA molecules; shorten as you age

Euchromatin

Loosely packed chromatin

Heterochromatin

highly condensed chromatin