Chapter 14- Part 3 Molecular Aspects of DNA replication Flashcards
What is the model organism for prokaryotic replication?
E. Coli- has single circular molecule of DNA
Explain Prokaryote replication.
Replication begins at one one Origen of replication - ori
Proceeded in both directions around the chromosome- bidirectional
Replicon- DNA controlled by an Origen
Ended at termination site
What is a replicon?
DNA controlled by an origin.
What does the replication in prokaryotes?
Replisomes replicates linear DNA in prokaryotes and terminates at the termination site
Do eukaryotes have one Origen or replication?
No it has multiple origins of replications because they have multiple large chromosomes.
Eukaryotic Replication is complicated by:
Large amount of DNA in multiple chromosomes and its liner structure but basic enzymology is the same but just more complex.W
Why do we neeed to use new enzymatic activity in eukaryotes?
Since they have ends and are linear we have to protect them via telomeres which are 400 to 500 repeat sequences that are attached to the ends of linear DNA in the eukaryotic cell.
What are telomeres?
Repeat sequences of 400> nucleotides that is attached to the ends of linear DNA in eukaryote cells which protect the DNA encoding genes.
What adds telemores to the ends of strands?
Telomerase
What happens without telemores?
important parts of DNA in the ends get lost
IS telemores present in prokaryotes?
No only in eukaryotes
Replication machinery aka..
Replisome
Two main components of replisome?
- Primosome- Primase, helicase, SSB, toposipmerase
- Complex of 2 DNA pol III- main replication enzyme- one for each strand.
What is the main replication enzyme?
COmplex of DNA pol II (2 one for each strand)
What does DNA polymerase I do?
Acts on lagging strand Replaces the RNA primer with deoxyribosenuclease
What does DNA polymerase II do?
Repairs issues with the DNA
What enzyme binds Okazaki fragments together?
DNA ligase
What enables DNA polymerase I to be able to act on the lagging strand?
Exonuclease
What is the exonuclease activity?
Coming in from the 3’ to 5’ end for proofreading in all three DNA polymerase
What only has 5’ to 3’ exonuclease activity?
DNA pol I has 5’ to 3’ exonuclease activity
What is a nuclease?
Enzyme that works on polynucleotides and breaks them down
What is deoxyribose nuclease?
Works on DNA and breaks it into deoxyrbose nucleotides
What is Ribonuclease
Works on RNA and breaks it into ribonucleotides
Exonuclease can come in anywhere from the_
end
Endonuclease can attack from the ___
Center
Example of endonuclease:
Eco R1- restriction endonuclese
What is a nick?
ONe phosphodiester bond is missing where DNA POL 1 came in and replaced RNA primer w/ DNA and previous synthesis ended just before primer
What seals nicks?
DNA ligases connecting the two fragments
How can DNA replication be supported when strand replication is happening in the opposite direction?
The lagging strand template loops around so it moves in the same direction as the leading strand.
DNA gyrase is what
Topoisomerase
In G1 how does cell prepare for S?
They make all the proteins aka helicase, primase, SSBS DNA gyrase, DNA polymerase III, I and II DNA ligase
DNA TO PROTEIN
