KA1.5 - Protein Control of Cell Division

Question 1

What is the cytoskeleton of a eukaryotic cell?

Answer 1

A network of proteins extending throughout the cytoplasm

Question 2

What is the function of the cytoskeleton in eukaryotic cells?

Answer 2

Gives mechanical support and shape to cells.

Question 3

State one of the proteins that makes up the cytoskeleton?

Answer 3

Microtubules

Question 4

What are microtubules composed of?

Answer 4

Hollow cylinders composed of the protein tubulin

Question 5

Where do microtubules radiate from?

Answer 5

They radiate from the microtubule organising centre (MTOC) or centrosome.

Centrosome not centromere

Question 6

List key functions of microtubules within the cell.

Answer 6

They control the movement of:
* Membrane-bound organelles (including secretory vesicles)
* Chromosomes (during mitosis and meiosis)

Question 7

What is required for remodelling of the cytoskeleton during cell division, and what processes are involved?

Answer 7

The formation and breakdown of microtubules, which requires polymerisation (build-up) or depolymerisation (break-down) of tubulin.

Question 8

What is the purpose of the cell cycle?

Answer 8

It regulates the growth and replacement of genetically identical cells throughout the life of the organism.

Question 9

What are the two main parts of the cell cycle?

Answer 9

• Interphase
• Mitotic (M) phase

Question 10

Name the three sub-phases of Interphase.

Answer 10

1. G1 phase
2. S phase
3. G2 phase

Question 11

What occurs during the G1 phase of interphase?

Answer 11

A growth phase where proteins and organelles are synthesised.

Question 12

What occurs during the S phase of interphase?

Answer 12

The DNA is replicated.

Question 13

What occurs during the G2 phase of interphase?

Answer 13

A further growth phase.

Question 14

What are the two main stages of the Mitotic (M) phase?

Answer 14

1. Mitosis
2. Cytokinesis

Question 15

Name the four stages of Mitosis.

Answer 15

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

PMAT

Question 16

Define ‘Cytokinesis’

Answer 16

The cytoplasm splits into two daughter cells.

Question 17

Describe the key events during Prophase of mitosis

Answer 17

• DNA condenses into chromosomes each with two sister chromatids.
• Nuclear membrane breaks down.
• Spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region.

Question 18

Describe the key event during Metaphase of mitosis.

Answer 18

Chromosomes are aligned at the metaphase plate (equator of the spindle).

Question 19

Describe the key event during Anaphase of mitosis.

Answer 19

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

Question 20

Describe the key events during Telophase of mitosis.

Answer 20

The chromosomes decondense, and nuclear membranes are formed around them.

Question 21

What are cell cycle checkpoints, and what is their purpose?

Answer 21

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

Question 22

Name the three main cell cycle checkpoints.

Answer 22

1. G1 checkpoint
2. G2 checkpoint
3. M checkpoint

Question 23

What proteins are involved in regulating cell cycle progression?

Answer 23

Cyclin proteins (accumulate during cell growth) combine with and activate cyclin-dependent kinases (CDKs).

Question 24

What do active CDKs do, and how does this affect cell cycle progression?

Answer 24

Active CDKs phosphorylate cell proteins. If sufficient phosphorylation is achieved, the cell cycle progresses.

Question 25

What is the role of Retinoblastoma protein (Rb) at the G1 checkpoint?

Answer 25

It acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.

Question 26

How does the cell progress from G1 to S phase at the G1 checkpoint?

Answer 26

Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb), which allows transcription of the genes needed for DNA replication.

Question 27

What is assessed at the G2 checkpoint?

Answer 27

The success of DNA replication and any DNA damage.

Question 28

What happens when DNA damage is detected at the G2 checkpoint (mentioning p53)?

Answer 28

DNA damage triggers the activation of several proteins, including p53, that can: * Stimulate DNA repair * Arrest (stop) the cell cycle * Cause cell death (apoptosis)

Question 29

What does the Metaphase checkpoint control, and when is progression halted?

Answer 29

It controls progression from metaphase to anaphase. Progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.

Question 30

What critical outcome does the metaphase checkpoint ensure?

Answer 30

Ensures each daughter cell receives the correct number of chromosomes.

Question 31

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

Answer 31

May result in a degenerative disease

Question 32

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

Answer 32

Tumour formation

Question 33

How can normal genes involved in cell growth/division contribute to tumour formation?

Answer 33

Normal genes called proto-oncogenes can mutate to form tumour-promoting oncogenes.

Question 34

What is apoptosis?

Answer 34

Programmed cell death

Question 35

Why is apoptosis important in the development?

Answer 35

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

Question 36

Give examples of external cell death signals that can trigger apoptosis.

Answer 36

* The production of death signal molecules from lymphocytes. * A lack of growth factors.

Question 37

Explain how a lymphocyte can trigger apoptosis in cells?

Answer 37

Lymphocytes produce cell death signals which bind to surface receptor protein and trigger a protein cascade within the cytoplasm.

Question 38

Give an example of an internal cell death signal that can trigger apoptosis.

Answer 38

DNA damage - which causes activation of the p53 tumour-suppressor protein.

Question 39

What type of molecules are activated by both external and internal death signals in apoptosis, and what is their function?

Answer 39

Caspases (a type of protease molecule). They cause the destruction of the cell by triggering the degradation of any protein molecule.