lecture 2

Question 1

what happens during the G1 phase?

Answer 1

everything but the chromosomes replicate

Question 2

what happens during the G2 phase?

Answer 2

error checks occur and the chromosomes are two sister chromatids

Question 3

what happens during the S phase?

Answer 3

DNA replicate

Question 4

What is the G0 phase?

Answer 4

cells have stopped dividing - quiescent phase

Question 5

When does mitosis truly begin?

Answer 5

prophase

Question 6

What is the order of the cell cycle?

Answer 6

G1, 
(G0)
S
G2
M

Question 7

What is mitosis 1 and mitosis 2?

Answer 7

1- upto and including metaphase

2 - anaphase and telophase

Question 8

How do E.coli replicate?

Answer 8

There is a bidirectional replication fork - opposite directions

Question 9

What is the point at which replication occurs called?

Answer 9

origin of replication

Question 10

What does the origin of replication form?

Answer 10

replication fork

Question 11

How is the leading strand synthesised?

Answer 11

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.

Question 12

How is the lagging strand synthesised?

Answer 12

• 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.

Question 13

How are the RNA primers removed?

Answer 13

ribonuclease removes them using exonuclease 5’ to 3’ activity

Question 14

What does repair DNA polymerase do?

Answer 14

it fills the gaps made by RNA primers with DNA

Question 15

What does DNA ligase do?

Answer 15

It uses ATP to join two okazaki fragments together

Question 16

What are single strands DNA binding proteins?

Answer 16

they prevent the single stranded DNA from folding

Question 17

What does the sliding clamp do?

Answer 17

it makes sure that the DNA polymerase is in the right place and doesn’t fall off

Question 18

Why is the lagging strand looped around?

Answer 18

so that both strands can be synthesised continuously

Question 19

What is the proofreading mechanism?

Answer 19

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.

Question 20

What kind of complex is formed during DNA synthesis?

Answer 20

multi enzyme complex

Question 21

How many origins of replications form in eukaryotes and what type of forks are they?

Answer 21

Eukarytoic DNA replication involves the formation of multiple origins of replication and the forks are bidirectional