18-19 DNA replication 2 Flashcards
(25 cards)
list the components of the OriC region in E. coli
DUE, IHF, R1-5, I1-4, HU proteins, FIS
what’s DUE?
DNA unwinding element. tandem repeats of 3*13bp with high AT content
what’s IHF
binding site for Integration Host Factor => opens and bends DNA
what’s R1-5?
binding sites for DnaA proteins. 5 repeats of a 9bp sequence
what’s I1-3?
additional DnaA binding sites
what are HU proteins?
histone like proteins that promote DNA bending
what’s FIS?
binding site for “factor for inversion stimulation” protein => helps open and bend DNA
DnaA proteins coupled with ATP bind to what?
R1-5 and the I1-3 repeats
where do IHF and FIS proteins bind and what do they all do?
bind to their respective sites, HU binds nonspecifically. induce DNA to wind around them
what happens in the DUE regions when the proteins overwind the other DNA?
Induces UNDERWINDING! opens up a bubble
helicase (DnaB) is assembled on what, with the help of what?
assembled on the lagging strands of both small replication forks (melted DUE region), with help of DnaC-ATP protein and hydrolysis of its ATP
what other proteins are required for DNA synthesis?
SSB, DNA Pol III, gyrase
what happens to DnaA proteins?
ATPases, slowly hydrolyze ATP to ADP. R1-5 bind DnaA-ATP and ADP equally. three I1-3 sites can only bind DnaA-ATP. slowly dissociates and destabilises overwound region.
oriC is rich in what sequence?
GATC
which base in GATC is methylated?
the A. immediately after replication all GATC is hemimethylated
what does hemimethylated oriC do?
binds to plasma membrane, stops new replication process from starting.
what enzyme methylates the new GATC? and how long does it take?
Dam methylase, about 20 minutes
what is Tus and what does it do?
Terminator Utilization Substance (a protein), binds to ter locus and inhibits helicase
what is Ter and what does it do?
several 20bp repeats oriented in opposite directions -> act like traps for the replication forks.
how do the two new circular chromosomes unlink?
via topoisomerase type II
how many replicator sites do humans have per chromosome?
100-600
what do eukaryotic cells not need and why?
don’t need a gyrase because unwinding DNA from histones leaves the helix in an underwound state already
what are telomeres and what do they do?
many short simple sequence repeats. stops the chromosomes from growing shorter.
what is TELOMERASE?
a protein-RNA complex, “reverse transcriptase” polymerase. actsa to extend parents stand, makes a complementary strand or T-loop which protects the end of telomeres
