IMED1002 Study Guide - Final Guide: Origin Recognition Complex, Eukaryotic Dna Replication, Dna Replication
LECTURE 16: CHROMOSOME REPLICATION
What are the functions of these proteins found at the replication fork?
Sliding clamp/PCNA – Allows DNA Pol. to bind stably therefore increasing replication efficiency
Clamp loader – Loads/attaches sliding clamps
Topoisomerase/gyrase – Helps prevent DNA strand from over-twisting
ssDNA-binding protein (RPA in particular) – Stabilises ssDNA to stop it reannealing with other strand
Replication of chromosomes is mainly regulated through controlling initiation. Initiation occurs at
the origin of replication (ori) where replication forks form in pairs and move in opposite directions to
create a replication bubble. The length and sequence of origins vary between species but they are
always AT-rich. Origins are also where replication proteins are assembled in an ordered fashion. The
first complex to bind is the ORC or origin recognition complex which contains multiple proteins that
separate the DNA strands and recruits other proteins. Eukaryotic chromosomes contain multiple
origins of replication.
Why does eukaryotic DNA replication need to be so coordinated and why are there multiple origins
of replication?
Multiple origins of replication make the process more efficient (takes less time) due to the massive
sizes of eukaryotic genomes. This is also a reason why replication needs to be coordinated – some
genes are only needed at particular times, some are needed at the same time - to regulate this we
need to regulate chromatin structure and hence activity.
What are the two distinct steps in initiation?
Licensing – where licensing factor bind to origin of replication
Initiation – replication starts happening
Wh a’t RNA priers at the ed of hroosoes e replaed DNA?
DNA Pol. alas eeds a 3’OH ed to ork fro hih is h repliatio is alas doe 5’ to 3’
e’re addig o to the 3’ ed eah tie. If teloeres did’t eist, he RNA priers are reoed,
the gap left ehid ould’t e filled i sie there is o 3’OH for DNA Pol. to start fro.
Describe how replication at telomeres happens/ the role of telomerase
Telomeres are tandem repeats (one after the other) of TTAGGG that are at the end of template
strands. Telomerase is an enzyme whose role is to extend telomeres. Its RNA part binds
complementarily to the telomere and this allows the DNA Pol. to extend the newly synthesized
strand further. Telomerase then slides along and allows DNA Pol. to keep adding extra nucleotides to
extend the telomere. Hence, even though a gap is still left when the primer is removed after DNA
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Document Summary
Sliding clamp/pcna allows dna pol. to bind stably therefore increasing replication efficiency. Topoisomerase/gyrase helps prevent dna strand from over-twisting ssdna-binding protein (rpa in particular) stabilises ssdna to stop it reannealing with other strand. Replication of chromosomes is mainly regulated through controlling initiation. Initiation occurs at the origin of replication (ori) where replication forks form in pairs and move in opposite directions to create a replication bubble. The length and sequence of origins vary between species but they are always at-rich. Origins are also where replication proteins are assembled in an ordered fashion. The first complex to bind is the orc or origin recognition complex which contains multiple proteins that separate the dna strands and recruits other proteins. Multiple origins of replication make the process more efficient (takes less time) due to the massive sizes of eukaryotic genomes. Licensing where licensing factor bind to origin of replication.
