Ch 14 DNA Synthesis and Repair

Bio 1113

Semiconservative replication

parent strands separate, half old, half new

Conservative replication

entire new helix forms

Dispersive replication

parent strands and new mixed in chunks

DNA Polymerase

replicates DNA 5’→3’

needs free 3’ OH to attach nucleotide

dNTPs

provides the energy for DNA synthesis

origin of replication/bubble

where replication starts

number of bubbles

Bacteria: 1

Eukaryotes: many

Primase

synthesizes RNA primer which provides 3’ OH to begin sythesis

Helicase

unzips DNA helix

SSBPs

stabilizes DNA strands

Topoisomerase

relieves twisting forces of the DNA

Telomere

end of chromosome, telomerase expands this

2 types of synthesis

lagging and leading

Leading strand synthesis

1. DNA is opened, unwound, and printed

2. synthesis

Lagging Strand Synthesis

1. primer added

2. first Okazaki fragment synth

3. second frag synth

4. primer replaced

5. gap closed

Replisome

all of the “machinery” for synthesis combined

two mechanisms of repair

proofreading and mismatch repair

proofreading definition

DNA pol 3 detects and corrects mismatched base pairs

Mismatch repair definition

corrected after replication by specialized proteins

Proofreading steps

1. DNA pol adds the wrong nucleotide

2. it pauses

3. corrects mistake using exonucleases ability (removes)

Mismatch repair steps

1. DNA is replicated incorrectly

2. Nucleotide excision repair aka removal and replacement of bases