Protein Control of Cell Division

Question 1

What is the role of the cytoskeleton?

Answer 1

To give mechanical support and shape to cells.

Question 2

What are microtubules?

Answer 2

Hollow cylinders composed of the protein tubulin.

Question 3

Where do microtubules radiate from?

Answer 3

The Microtubule Organising Centre (MTOC).

Question 4

What is the role of microtubules?

Answer 4

To control the movement of membrane-bound organelles and chromosomes.

Question 5

What does the formation and breakdown of microtubules involve?

Answer 5

Polymerisation and depolymerisation of tubulin.

Question 6

What forms the spindle fibres that are active during cell division?

Answer 6

Microtubules.

Question 7

What are the phases of the cell cycle?

Answer 7

Interphase and mitotic (M) phase.

Question 8

What does mitotic phase involve?

Answer 8

Mitosis and cytokinesis.

Question 9

What does interphase involve?

Answer 9

G1 (Growth phase), S Phase (when DNA is replicated) and G2 (further growth phase).

Question 10

What are the phases of mitosis?

Answer 10

Prophase, metaphase, anaphase and telophase.

Question 11

What happens during prophase?

Answer 11

The DNA condenses into chromosomes each consisting of two sister chromatids. The nuclear membranes break down and spindle fibres extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region.

Question 12

What happens during metaphase?

Answer 12

Chromosomes align at the metaphase plate (equator).

Question 13

What happens during anaphase?

Answer 13

Spindle microtubules shorten by depolymerisation, sister chromatids are separated and the chromosomes are pulled to opposite poles.

Question 14

What happens during telophase?

Answer 14

The chromosomes decondense and nuclear membranes are formed around them.

Question 15

What are checkpoints?

Answer 15

Mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next stage unless certain requirements are met.

Question 16

When do cyclin proteins accumulate?

Answer 16

During cell growth.

Question 17

What are cyclin proteins involved in?

Answer 17

Regulation of the cell cycle.

Question 18

What activated cyclin-dependent kinases (CDK)?

Answer 18

The binding of cyclin.

Question 19

What is the role of active cyclin-dependent kinases?

Answer 19

To phosphorylate proteins that regulate progression through the cell cycle. If sufficient phosphorylation occurs progression occurs.

Question 20

When does the G1 checkpoint occur?

Answer 20

Towards the end of G1.

Question 21

How do retinoblastoma (Rb) act as a tumour suppression?

Answer 21

By inhibiting transcription of genes that code for proteins needed for DNA replication.

Question 22

What inhibits the retinoblastoma?

Answer 22

Phosphorylation by G1 cyclin-CDK.

Question 23

What is assessed at the G2 checkpoint?

Answer 23

The success of DNA replication and any damage to the DNA.

Question 24

What does DNA damage trigger?

Answer 24

The activation of several proteins such as p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.

Question 25

What does the metaphase checkpoint control?

Answer 25

Progression from metaphase to anaphase.

Question 26

What happens at the metaphase checkpoint?

Answer 26

Progression is halted until the chromosomes are aligned correctly at the metaphase plate and attached to the spindle fibres.

Question 27

What may an uncontrolled reduction in the rate of the cell cycle result in?

Answer 27

Degenerative disease.

Question 28

What may an uncontrolled increase in the rate of the cell cycle result in?

Answer 28

Tumour formation.

Question 29

What is a proto-oncogene?

Answer 29

A normal cell, usually involved in cell growth or division, that can mutate to form a tumour promoting oncogene.

Question 30

What is apoptosis?

Answer 30

Programmed cell death that can be triggered by internal or external death signals.

Question 31

What is an example of an external death signal?

Answer 31

The production of death signal molecules from lymphocytes.

Question 32

What is an example of an internal death signal?

Answer 32

DNA damage.

Question 33

How do external death signals trigger apoptosis?

Answer 33

By binding to surface receptor proteins and triggering a protein cascade within the cytoplasm.

Question 34

What does an internal death signal resulting from DNA damage cause?

Answer 34

Activation of p53 tumour suppressor protein.

Question 35

What are caspases?

Answer 35

Types of protease enzyme.

Question 36

What do both types of signal result in?

Answer 36

Activation of caspases that cause the destruction of the cell.

Question 37

Why is apoptosis essential during the development of an organism?

Answer 37

As it removes cells no longer required as development progresses or during metamorphosis.

Question 38

When else may cells initiate apoptosis?

Answer 38

In the absence of growth factors.