Schwabe 4 DNA replication Flashcards
DNA pol 1 catalyses:
(DNA)n + dNTP (DNA) n+1 + PPi
Requires: dNTPs , Mg 2+ Template, Primer w/ free 3’-OH
Pysophosphatase
function
pulling reaction across to right PPi -> 2Pi= equilibrium
Chain elongation
5’->3’
pol I function
DNA repair.
Removes mismatched nucelotides “proof reading” &
Finds ss Break (nick)
detects wider/narrower distance of non-matching nucelotides t=t distorts H- bonding,
removes several nucleotides
PolA1 mutant
Only ~1% of polymerase activity, both nuclease activities normal, DNA replication normal, UV sensitive,
DNA Pol I
size
responsible for
Single polypeptide Mr 103,000 Contains Zn 2+ 3 distinct structural functional domains, each responsible for 1 of polymerase/nuclease activities & shield active sites.
DNA pol II & pol III
Requirements:
• dNTPs & Mg2+, template, primer w/ free 3’OH
Activities: 5’-> 3’ polymerase
3’ -> 5’ exonuclease =Yes
5’->3’ nuclease =No
Processivity
of Pol III & II
Pol III very high >500x10^3 => major role in DNA replication, clamp loader 20A’ wide
Pol II moderate ~1,5000
Rate
Pol III & II
Pol III very high >10^3 per sec
Pol II low
DNA Pol III
size
mr 900,000 MULTIMERIC ENZYME= least 10 subunits each has specific properties
“holoenzyme”
Αβχϒδδ’ετθψ
“core enyme”
α + ε + θ
REPLICATION OF E.COLI CHROMOSOMES
Bi-directional replication starts at unique site ORIGIN to TERMINATION point opposite origin. 2 replication forks assemble in opposite directions, each acts as template.
REPLICATION FORK:
region of DNA undergoing simultaneous unwinding, strand separation & replication E.coli chromosome.
DNA Polymerase needs
–OH grp on 3’ hence unidirectional
