Protein Control Of Cell Division

Question 1

What is a cytoskeleton and what is its function ?

Answer 1

The cytoskeleton is a network of proteins through the membrane , it’s also re forming (dynamic)

It gives mechanical support to a cell

Question 2

What are cytoskeletons proteins made of ?

Answer 2

Microtubules

Question 3

Where are microtubules found and what are they made of

Answer 3

Micro tubules are found in all eukaryotic cells

Microtubules are hollow cylinders composed of the protein (globular)tubulin. They radiate from the microtubule organising centre (MTOC) or centrosome.

Question 4

What is the function of microtubules

Answer 4

They control the movement of membrane bound organelles and chromosomes

Question 5

What does cell division involve ?

Answer 5

Remodelling of the cytoskeleton

Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin
Microtubules form the spindle fibres that are active during cell division

Question 6

What different processes are in the cell cycle ?

Answer 6

Consists of the interphase and mitotic phase

Question 7

Why is the cell cycle important ?

Answer 7

It’s required for the growth and repair

Question 8

Describe the Inter phase?

Answer 8

It consists of 3 phases

G1
S phase
G2

Interphase involves growth and DNA synthesis including G1, a growth phase(proteins and organelles are made ); S phase, during which the DNA is replicated; and G2, a further growth phase(proteins and organelles are synthesised)

Question 9

Describe the mitotic phase ?

Answer 9

At the end of the G2 a cell enters the mitotic phase

It is divided into 2 stages , mitosis and cytokenises

In mitosis the chromosomal material is separated by the spindle microtubules. This is followed by cytokinesis, in which the cytoplasm is separated into two daughter cells.

Question 10

What are the 4 stages of mitosis ?

Answer 10

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

Question 11

Describe what goes on during the prophase

Answer 11

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.

Question 12

Describe the metaphase?

Answer 12

Metaphase — chromosomes are aligned at the metaphase plate (equator of the spindle)

Question 13

Describe the anaphase ?

Answer 13

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

Question 14

Describe the telophase ?

Answer 14

Telophase — the chromosomes decondense and nuclear membranes are formed around them.

Question 15

Function of the microtubules in the cell cycle ?

Answer 15

Aligning chromosomes to the metaphase plate

Separating sister chromatids

Formation of daughter nuclei

Question 16

Control of the cell cycle how does this happen ? And why is this control important

Answer 16

This control is important because timing and rate of cell division is very important , this will vary with different cell types

The control happens through checkpoints , 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 17

Name the different checkpoints?

Answer 17

G1 checkpoints - sufficient cell growth must have happened before it goes to the S phase

G2 checkpoint- success of DNA replication is assessed

M checkpoint- occurs during the metaphase and controls entry to the anaphase , checks if chromosomes are aligned properly, makes sure the daughter cell has the right amount of chromosomes

Question 18

Describe the G1 checkpoint

Answer 18

G1 is the most important

If a cell doesn’t get a go signal it will undergo G0 phase which is not dividing , if the signal is go then…

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
Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb). This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.

Question 19

Describe the G2 checkpoint?

Answer 19

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

When DNA is damaged it activates the activation of several proteins including p53 , this can stimulate DNA repair , arrest the cell cycle or cause cell death

Question 20

Describe the M checkpoint?

Answer 20

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

Question 21

What can happen if cell cycle rate is not controlled ?

Answer 21

May cause the formation of degenerate diseases

An uncontrolled increase in the rate of the cell cycle may result in tumour formation

Question 22

What happens when tumours are formed?

Answer 22

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

Question 23

Describe apoptosis ?

Answer 23

Apoptosis is triggered by cell death signals that can be external or internal

Question 24

How do external death signals work ?

Answer 24

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

Example -production of the signals from lymphocytes

Question 25

Describe internal death signals ?

Answer 25

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

Question 26

Extra facts

Answer 26

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

Question 27

Why is apoptosis important?

Answer 27

It is important during development of an organism , as they remove cells that are no longer required in development or during metamorphosis

Or they can do it in the absence of growth factors