5 - protein control of cell division

Question 1

Describe the role of the cytoskeleton.

Answer 1

gives mechanical support and shape to cells

Question 2

Describe the structure of the cytoskeleton.

Answer 2

It consists of different protein structures including microtubules, which are found in all eukaryotic cells.

Question 3

What do microtubules control?

Answer 3

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

Question 4

state

Answer 4

Cell division requires remodelling of the cytoskeleton

Question 5

Describe the formation and breakdown of microtubules in terms of polymerisation and depolymerisation of tubulin

Answer 5

Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin.

Question 6

Describe the role of microtubules in cell division.

Answer 6

Microtubules form the spindle fibres that are active during cell division.

Question 7

What two phases does the cell cycle consist of?

Answer 7

interphase and mitotic phase

Question 8

Name the three stages of interphase and describe the processes which take place during each stage.

Answer 8

G1, a growth phase; S phase, during which the DNA is replicated; and G2, a further growth phase.

Question 9

What does the mitotic phase involve?

Answer 9

The mitotic phase involves mitosis and cytokinesis

Question 10

What does mitosis consist of? And describe the events taking place in each stage.

Answer 10

Mitosis consists of prophase, metaphase, anaphase and telophase.
- Prophase = DNA condenses into chromosomes each consisting of 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.
- Metaphase = chromosomes are aligned at the metaphase plate (equator of the spindle).
- Anaphase = as spindle microtubules shorten by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles.
- Telophase = the chromosomes decondense and nuclear membranes are formed around them.

Question 11

What is progression through the cell cycle controlled by?

Answer 11

checkpoints

Question 12

Describe the role of checkpoints.

Answer 12

Checkpoints are 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 13

Describe the role of cyclin proteins in regulating the cell cycle.

Answer 13

Cyclins combine with and activate cyclin-dependent kinases (CDKs). Active cyclin-CDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.

Question 14

Describe the role of retinoblastoma protein (Rb) at the G1 checkpoint.

Answer 14

At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.

Question 15

What happens at the G2 checkpoint?

Answer 15

At the G2 checkpoint, the success of DNA replication and any change to DNA is assessed.

Question 16

state

Answer 16

DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.

Question 17

Describe the role of the metaphase checkpoint.

Answer 17

The metaphase checkpoint 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 18

state

Answer 18

An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease and an uncontrolled increase in the rate of the cell cycle may result in tumour formation.

Question 19

state

Answer 19

A proto-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene.

Question 20

What is apoptosis triggered by?

Answer 20

cell death signals that can be external or internal

Question 21

Give an example of an external death signal and an internal death signal.

Answer 21

The production of death signal molecules from lymphocytes is an example of an external death signal.

Question 22

Describe how external death signal molecules bring about apoptosis.

Answer 22

External death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm.

Question 23

Describe how internal death signal molecules bring about apoptosis.

Answer 23

An internal death signal resulting from DNA damage causes activation of p53 tumour-suppressor protein.

Question 24

state

Answer 24

Both types of death signal result in the activation of caspases (types of protease enzyme) that cause the destruction of the cell.

Question 25

Explain why apoptosis is essential during development of an organism.

Answer 25

Apoptosis is essential during development of an organism to remove cells no longer required as development progress or during metamorphosis.

Question 26

state

Answer 26

cells may initiate apoptosis in the absence of growth factors.