lecture 2 Flashcards
(21 cards)
what happens during the G1 phase?
everything but the chromosomes replicate
what happens during the G2 phase?
error checks occur and the chromosomes are two sister chromatids
what happens during the S phase?
DNA replicate
What is the G0 phase?
cells have stopped dividing - quiescent phase
When does mitosis truly begin?
prophase
What is the order of the cell cycle?
G1, (G0) S G2 M
What is mitosis 1 and mitosis 2?
1- upto and including metaphase
2 - anaphase and telophase
How do E.coli replicate?
There is a bidirectional replication fork - opposite directions
What is the point at which replication occurs called?
origin of replication
What does the origin of replication form?
replication fork
How is the leading strand synthesised?
Dna primase creates a short RNA primers and the DNA polymerase adds nucleotides to the 3 prime end so the new strand is snthesised in the 5 prime to 3 prime direction. DNA synthesis of the leading strand is continuous because it’s 3’ end is in the same direction as the movement of the replication fork.
How is the lagging strand synthesised?
- A type of RNA polymerase called DNA Primase synthesises a short RNA fragment. The fragment is removed at a later stage of replication.
- DNA synthesis of the lagging strand is discontinuous - DNA is synthesised in short pieces called okazaki fragments.
- DNA polymerase adds nucleotides to the 3’ end of the RNA primer and continues to synthesise the okazaki fragment until it reaches the end of the previous Okazaki fragment.
- RNA primer of previous okazaki fragment is removed and replaced by DNA.
- DNA ligase joins the two adjacent okazaki fragments.
How are the RNA primers removed?
ribonuclease removes them using exonuclease 5’ to 3’ activity
What does repair DNA polymerase do?
it fills the gaps made by RNA primers with DNA
What does DNA ligase do?
It uses ATP to join two okazaki fragments together
What are single strands DNA binding proteins?
they prevent the single stranded DNA from folding
What does the sliding clamp do?
it makes sure that the DNA polymerase is in the right place and doesn’t fall off
Why is the lagging strand looped around?
so that both strands can be synthesised continuously
What is the proofreading mechanism?
Ensures no mistakes are made because mutations can be dangerous.
Before adding a new nucleotide, DNA polymerase checks to make sure previous nucleotide is correct.
If it isn’t they are removed by exonuclease activity of DNA polymerase in the 3’ to 5’ direction.
What kind of complex is formed during DNA synthesis?
multi enzyme complex
How many origins of replications form in eukaryotes and what type of forks are they?
Eukarytoic DNA replication involves the formation of multiple origins of replication and the forks are bidirectional
