Cell Cycle and DNA Replication

Question 1

In which phase of the cell cycle does DNA replication occur?

Answer 1

S phase

Question 2

What occurs in the G1 phase of the cell cycle?

Answer 2

Cell content replication (organelles develop)

Question 3

What occurs in the G2 phase of the cell cycle?

Answer 3

Double check and repair, enzymes and poteins are synthesised

Question 4

What occurs in the M phase of the cell cycle?

Answer 4

Cell division

Question 5

What is the order of the cell cycle?

Answer 5

G1, S, G2, M

Question 6

What are cyclins?

Answer 6

Proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase enzymes.

Question 7

What is DNA Helicase?

Answer 7

An enzyme that unwinds DNA double helix to separate the two parental strands and make them available as template strands.

Question 8

What is an exonuclease?

Answer 8

An enzyme that cuts nucleotides at the end of the polynucleotide chain

Question 9

What is an endonuclease?

Answer 9

An enzyme that cuts nucleotides in the middle (not the ends) of the polynucleotide chain

Question 10

What is the function of DNA Polymerase?

Answer 10

DNA Polymerase is responsible for assembling nucleotides

Question 11

What is the function of an exonuclease domain in a DNA Polymerase?

Answer 11

Responsible for the recognition and excision of mispaired bases (proofreading mechanism)

Question 12

How could a mutation in the exonuclease domain of DNA Polymerase cause tumours?

Answer 12

No proofreading would occur so any mispaired bases would not be excised. This would lead to the accumulation of mutations and the formation of a tumour as the DNA becomes more unstable.

Question 13

Which enzyme joins Okazaki fragments?

Answer 13

DNA ligase

Question 14

What is stage G0?

Answer 14

G0 stage is a resting stage in which cells do not continue through the cell cycle (eg when nerve/cardiac cells are mature)

Question 15

What is a replication fork?

Answer 15

This is a Y-shaped region on a replication DNA molecule where new strands are being synthesised

Question 16

What are Okazaki fragments?

Answer 16

These are short, newly synthesised DNA fragments that are formed on the lagging strand during DNA replication

Question 17

What are required to initiate DNA replication?

Answer 17

RNA primers

Question 18

What is the leading strand?

Answer 18

Strand of DNA that is synthesised continuously in the 5’ to 3’ direction

Question 19

In which direction does DNA polymerase work?

Answer 19

5’ to 3’

Question 20

What is the lagging strand?

Answer 20

Strand of DNA that is synthesised discontinuously in short Okazaki fragments (away from the replication fork)

Question 21

Why might there be a problem with producing the final Okazaki fragment on the lagging strand?

Answer 21

This is due to the end replication problem. RNA primer is removed so the DNA at the end is not replicated. This would lead to the DNA getting shorter after every replication.

Consequence - could possibly result in certain genes not being expressed.

Question 22

What mechanism is in place to overcome the end replication problem?

Answer 22

Telomerase adds repetitive nucleotide sequences to the ends of DNA (telomeres). Therefore, the telomeres get shorter every time, not the DNA.

Question 23

What is topoisomerase?

Answer 23

Topoisomerase binds to DNA and cuts the phosphate backbone during DNA replication. If left unabated, the torsion would stop the ability of DNA to replicate.

Question 24

What is non-homologous end joining?

Answer 24

A pathway that repairs double-strand breaks in DNA by joining the two ends of DNA together

Question 25

What is a potential problem with non-homologous end joining?

Answer 25

If there has been a beak in the DNA, the ends are still joined together but that part of DNA is lost.

Question 26

What are chromosomal translocations?

Answer 26

A piece of DNA is translocated to another chromosome

Question 27

What are chromosomal inversions?

Answer 27

A whole gene within the DNA is inverted