Unit 1: KA5 - Protein Control of Cell Division

Question 1

What is the cytoskeleton?

Answer 1

The cytoskeleton is a network of protein fibres inside the cell. It’s function is to provide mechanical support and shape to cells.

Question 2

What is the cytoskeleton made of?

Answer 2

Different protein structures including microtubules (in eukaryotes).

Question 3

What are microtubules?

Answer 3

Hollow cylinders composed of protein tubulin.

Question 4

What is the function of microtubules?

Answer 4

They control the movement of membrane bound organelles and chromosomes.

Question 5

What does microtubules’ formation and breakdown involve?

Answer 5

polymerisation and depolymerisation

Question 6

What does cell division require?

Answer 6

remodelling of the cytoskeleton

Question 7

What are spindle fibres?

Answer 7

When the cytoskeleton is remodelled, the disassembled microtubules form the spindle fibres.

Question 8

What function do spindle fibres perform?

Answer 8

The spindle fibres control the movement of chromosomes during mitosis.

Question 9

What are the two phases of the cell cycle?

Answer 9

• Interphase

- Mitotic phase

Question 10

What are the stages within the mitotic phase?

Answer 10

Prophase 
Meta phase
Anaphase
Telophase
Cytokinesis

Question 11

Describe prophase.

Answer 11

• DNA condenses into chromatid pairs
• Nuclear membrane breaks down
• Spindle microtubules extend from centrosome to attach to chromosomes

Question 12

What is the centrosome?

Answer 12

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

Question 13

Describe metaphase.

Answer 13

• Chromosomes line up at the metaphase plate (equator).

Question 14

Describe Anaphase.

Answer 14

• Spindle microtubules shorten by depolymerisation

- Sister chromatids are separated and the chromosomes are pulled to opposite poles.

Question 15

At what point do spindle fibres attach to chromosomes?

Answer 15

The kinetochore

Question 16

Describe Telophase

Answer 16

• Nuclear membrane forms around chromosomes

- Chromosomes begin to uncoil (decondense).

Question 17

Describe cytokinesis

Answer 17

• Separation of the cytoplasm to form 2 identical daughter cells.

Question 18

What is progression through the cell cycle regulated by?

Answer 18

Checkpoints

Question 19

What are the 3 sections of interphase, and describe them

Answer 19

G1 - Growth: growth of proteins and organelles
S - Synthesis: DNA replication
G2 - Growth: growth of proteins and organelles

Question 20

What proteins are involved in regulating the cell cycle?

Answer 20

cyclins

Question 21

What does the Retinoblastoma protein do?

Answer 21

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 22

How is Rb deactivated?

Answer 22

phosphorylation by G1 cyclin-CDK

Question 23

What is assessed at the G2 checkpoint?

Answer 23

Success of DNA replication

damage to DNA

Question 24

What is G₀?

Answer 24

If the cell does not pass the G1 checkpoint, it enters G₀, a resting phase.

Question 25

What is CDK?

Answer 25

Cyclin Dependent Kinase.

Question 26

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

Answer 26

Formation of a tumour

Question 27

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

Answer 27

a degenerative disease

Question 28

What 3 checkpoints are there?

Answer 28

G1 G2 Metaphase

Question 29

Name the protein that is activated by DNA damage.

Answer 29

p53

Question 30

What 3 things can p53 do after identification of cell damage at the G2 checkpoint.

Answer 30

- Stimulation of DNA repair - Cause cell death - Arrest of cell cycle

Question 31

What does the metaphase checkpoint assess?

Answer 31

Ensure chromosomes are aligned correctly on metaphase plate and attached to the spindle microtubules.

Question 32

Define the term proto-oncogene

Answer 32

A proto-oncogene is a normal gene that is involved in the control of cell growth or division.

Question 33

Describe the effects of a mutation within a proto onco-gene.

Answer 33

formation of a tumour promoting oncogene.

Question 34

Define the term apoptosis.

Answer 34

Apoptosis is the carefully controlled destruction of cells.

Question 35

How is apoptosis triggered?

Answer 35

Internal or external death signals

Question 36

What two processes are apoptosis required in?

Answer 36

- Development of an organism | - metamorphosis

Question 37

Describe how external death signals work and give an example of a molecule that produces one.

Answer 37

Death signals can be produced by lymphocytes | These signal molecules bind to receptor proteins on surface of cell and trigger a protein cascade of caspase proteins

Question 38

What is caspase?

Answer 38

A type of protease that causes the destruction of the cell by triggering degradation of any protein.

Question 39

Describe the internal pathway of apoptosis.

Answer 39

A death signal is created and activates p53. | Cells may initiate apoptosis in the absence of growth factors.

Question 40

Give examples of internal death signals

Answer 40

- DNA damage activates p53 | - absence of growth factors