Class 10 - Prokaryotic and Eukaryotic DNA Replication Flashcards
How does DNA helicase load on DNA? How is this diff in prokaryotes and eukaryotes?
In Bacteria DNA melting occurs with ATP (double helix dissociated into single coils) and then ATP is used for helicase to bind and separate strands
In Eukaryotes ATP is used for helicase to load. ATP is used for DNA melting and strands are seperated
How does DNA helicase bind? How does it move in prokaryotes and eukaryotes?
DNA helicase binds ATP –> ADP + Pi
In prokaryotes helicase moves 5’ to 3’ on the lagging strand
6 subunits are in the ring
In eukaryotes helicase moves 3’ to 5’ in the leading strand
many more subunits are recruited
What does ciproflaxin do? Does this happen in prokaryotes or eukaryotes?
ciproflaxin is a drug that inhibits DNA topoisomerase II in prokaryotes only
What does the pol “alpha” subunit of eukaryotic DNA polymerase do?
functions in replication (with RNA primase)
no exonuclease activity
What does the pol “delta” subunit of eukaryotic DNA polymerase do?
functions in replication (processive DNA synthesis on the LAGGING strand)
exonuclease in the 3’ to 5’
[remember DNA is synthesized 5’ to 3’]
What does the pol “e” subunit of eukaryotic DNA polymerase do?
functions in replication (processive DNA synthesis on the LEADING strand
exonuclease in the 3’ to 5’
[remember DNA is synthesized 5’ to 3’]
What are the differences in the replication fork in prokaryotes and eukaryotes?
Eukaryotic DNA replication needs many replication forms
prokaryotic DNA replication uses a single origin to replicate the whole genome
Are histones primarily found in prokaryotes or eukaryotes? And what do they do in DNA replication?
Histones are mostly found in eukaryotes
Immediately after replication fork, recycles histones are reassembled into a nucleosome
As the replication form passes we need to reassemble the nucleosome
Unsure how they stay intact or break apart?
Remember histones associate with negative DNA through positive amino acids
Do prokaryotes or eukaryotes have multiple sites of replication?
Eukaryotic DNA replication needs many replication forks ==> replication bubble where helicases load
replication bubbles converge together
Prokaryotic DNA replication uses a single origin to replicate the whole genome
Prokaryotes have circular DNA but eukaryotes have linear chromosomes. What problem arises in replication with eukaryotic DNA?
DNA replication occurs continuously on the leading strand 5’ to 3’. DNA replication occurs discontinuously on the lagging strand using Okazaki fragments because it must go 5’ to 3’
As DNA replication approaches the end of a linear chromosome, a problem develops in the lagging strand. The RNA primer at the end of the chromosome is degraded. The newly synthesized strand is shorter at both 5’ ends resulting in 3’ overhangs
After RNA primers are removed, OVERHANG is on 3’ end. If this is not fixed, every cycle the DNA will get shorter
What is the solution for 3’ overhand end replication program in eukaryotes?
Telomeres form a repetitive sequence cap unique to the species – repeats this many times
telomeres form on both ends of the chromosome
Telomerase is an enzyme that adds telomeres
What are the components of telomerase?
Telomerase is an enzyme that adds telomeres to the ends of chromosomes. Telomerase has an RNA and protein component.
- RNA template
- catalytic protein that has reverse transcriptase activity to make DNA from RNA template
How does telomerase address the 3’ overhang?
- telomerase binds to the 3’ G-rich tail
- telomerases uses reverse transcriptase activity to synthesize complementary DNA on the 5’ strand that does not have overhang (template)
- telomerase continues to add to overhang and telomerase makes complementary DNA to this section
- telomerase is released and RNA primase builds a primer for DNA polymerase to fill in the gap 5’ to 3’
- the primer is removed and the gaps are sealed by DNA ligase
the 3’ OH that still remains forms a structure with telomere binding protein to protect the ends of chromosomes from damage and nuclease attack
