Protein control of Cell Division

Question 1

Define the cytoskeleton

Answer 1

A network of protein fibres extending through the cytoplasm in eukaryotes.

Question 2

Discuss the composition of microtubules.

Answer 2

Hollow, multiple subunits and composed of tubulin.

Question 3

What are the two faces of the cell cycle?

Answer 3

1. Interphase.
2. Mitotic phase.

Question 4

Discuss what occurs in every stage of the cell cycle.

Answer 4

G1: New proteins are made and organelles copied.
S: DNA Replication.
G2: A second stage of growth
M: Nuclear division and cytokenisis.

Question 5

Define PMAT.

Answer 5

1. Prophase.
2. Metaphase
3. Anaphase
4. Telophase

Question 6

Discuss the Prophase of the cell cycle (4).

Answer 6

1. DNA condenses until each chromosome is seen as two chromatids.
2. Nuclear membrane begins to disintegrate.
3. Chromosones begin to move to the centre
4. Spindle fibres extend from the MTOC by polymerisation and attach to chromosones.

Question 7

Discuss the metaphase of the cell cycle (3).

Answer 7

1. Nuclear membrane has now gone.
2. Chromosomes align along the equator
3. kinetochore at the centre of chromosome has attached to spindle fibres.

Question 8

Discuss the anaphase of the cell cycle (2).

Answer 8

Spindle fibres shorten as subunits are removed by depolymerisation and pulling chromatids towards the poles.
2. Chromatids can now be called chromosomes.

Question 9

Discuss the telophase of the cell cycle (2).

Answer 9

1. Chromosomes begin to condense.
2. Nuclear membrane begins to reform.

Question 10

What contracts during cytokinesis.

Answer 10

Actin.

Question 11

Name the location of the three checkpoints in the cell cycle.

Answer 11

1. End of G1
2. End of G2
3. During mitosis

Question 12

Discuss CDKs.

Answer 12

1. As cell size increases during G1, cyclins build up and combine with kinase.
2. CDK’s phosphorylate proteins that stimulate the cell cycle.
3. If sufficient phosphorylation occurs the cell progresses onto the next stage.

Question 13

Discuss the role of retinoblastoma in the cell cycle (4).

Answer 13

1. Rb inhibits the cell cycle by inhibiting the gene expression of proteins involved in DNA replication.
2. It does so by binding to transcription factors necessary for S phase.
3. Rb must become hyperphosphorylated by CDKs making it no longer bind to transcription factors.
4. Rb remains phosphorylated through S, g2 and M phases but is gradually dephosphorylated as the cell cycle progresses.

Question 14

Discuss the role of the G2 checkpoint.

Answer 14

Success of DNA replication assessed and any DNA damage will trigger a number of proteins, including p53.

Question 15

What can p53 cause?

Answer 15

1. Cell arrest.
2. DNA repair
3. Cell death

Question 16

Discuss the role of the M checkpoint.

Answer 16

Ensures chromosomes are attached to spindle microtubules before progression occurs.

Question 17

What is the protease involved in apoptosis.

Answer 17

Caspases.

Question 18

Discuss the role of caspases in apoptosis,

Answer 18

They breakdown/degrade proteins in the cell.