DNA & Replication Flashcards
structure of a nucleotide
phosphate group @ 5’ C, 5-Carbon sugar, and nitrogenous base @ 3’ C
what type of bond joins the 3’ and 5’ carbons of nucleotides?
phosphodiester linkage
base-pairing rules
AT
GC
identify hydroxyls, pentose sugar, and # Cs in sugar
3’ hydroxyl groups, 5’ phosphate groups, 5 Cs in sugar
Proteins involved in DNA replication
DNA polymerase I (primer removal and replacement), II (repair), III (main synthesis)
DNA pol I
5’-3’ exonuclease activity - removal of primers
3’-5’ exonuclease activity - proofreading
What do all DNA pols require to initiate synthesis?
3’ OH group (provided by RNA primer)
Leading strand (direction)
continuous synthesis directly following opening of fork(5’–>3’_
Lagging strand (direction)
discontinuous synthesis following opening of fork = fragments (5’–>3’)
steps of lagging strand synthesis
- primer is added
- DNA pol III –> 1st okazaki frag
- Primase & DNA pol III syn. 2nd okazaki frag
- DNA pol I removes primer & replaces w/ DNA
- DNA ligase closes gap
why do mutations that inactivate the 3’-5’ exonuc activity of DNA pol III greatly increase the frequency of mutations
mutation = no proofreading, so the mutations increase
what effect do mutations that inactivate the 5’-3’ exonuc activity of DNA pol I have?
there would be no removal of primers, so they could not be replaced with DNA, disrupting replication
3 types of mistake repair in DNA rep
proofreading, mismatch repair, nucleotide-excision repair
function of primers in DNA rep
RNA primers provide the 3’ OH for DNA pol
pyrimidines
Cytosine, Thymine, Uracil
