Unit 1 Cells and Proteins: Key Area 5 - Protein Control of Cell Division

Question 1

What is the cytoskeleton and what does it consist of?

Answer 1

A complex network of protein filaments that give mechanical support and shape to cells. It consists of different protein structures including microtubules, which are found in all eukaryotic cells.

Question 2

What are microtubules?

Answer 2

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

Question 3

What do microtubules control?

Answer 3

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

Question 4

What can microtubules form?

Answer 4

These microtubules also form the spindle fibres that are active during cell division. This means that the cytoskeleton needs remodelled during cell division.

Question 5

What does the formation and breakdown of microtubules involve?

Answer 5

Polymerisation and depolymerisation of tubulin.

Question 6

What are the 2 phases in the cell cycle?

Answer 6

Interphase and Mitotic phase (M phase).

Question 7

What does the interphase involve?

Answer 7

Growth and DNA synthesis including:

• G1 (Growth phase).
• S (Phase where DNA is replicated).
• G2 (Further growth phase).

Question 8

Why does the mitotic phase involve?

Answer 8

Mitotic phase involves mitosis and cytokinesis.

Question 9

What is mitosis?

Answer 9

Separation of chromosomal material spindle microtubules.

Question 10

What is cytokinesis?

Answer 10

Separation of the cytoplasm into 2 daughter cells.

Question 11

What are the 4 phases in mitosis?

Answer 11

Prophase, Anaphase, Metaphase, Telophase.

Question 12

Why happens in the Prophase?

Answer 12

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 13

What happens in the Metaphase?

Answer 13

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

Question 14

What happens at the Anaphase?

Answer 14

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

Question 15

Whthappens in the telophase?

Answer 15

The chromosomes decondense and nuclear membranes are formed around them.

Question 16

What happens in cytokinesis?

Answer 16

In animal cells the cytoplasm is divided into two by a contractile ring of actin and myosin which pinches in the cell to create two daughter cells.

Question 17

What is the progression of the cell cycle controlled by?

Answer 17

Checkpoints

Question 18

How do cyclin proteins accumulate and what are they involved in?

Answer 18

Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle.

Question 19

How does cyclin regulate the cell cycle?

Answer 19

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 20

What are checkpoints?

Answer 20

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 21

What are the 3 checkpoints in the cell cycle?

Answer 21

G1, G2 and Metaphase checkpoint.

Question 22

What happens at the G1 checkpoint?

Answer 22

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 23

What does the phosphorylation by G1 cyclin-CDK do?

Answer 23

Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb).

Question 24

What happens if the retinoblastoma protein is inhibited by G1 cyclin-CDK?

Answer 24

This allows transcription of the genes that code for proteins needed for DNA replication so cells progress from G1 to S phase.

Question 25

What happens at the G2 checkpoint?

Answer 25

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

Question 26

What does DNA damage at the G2 checkpoint trigger?

Answer 26

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

Question 27

If the G2 checkpoint passes where does the cell progress to?

Answer 27

The M phase

Question 28

What does the metaphase checkpoint control?

Answer 28

A metaphase checkpoint controls progression from metaphase to anaphase.

Question 29

At the M phase when is cell cycle halted until?

Answer 29

Here progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.

Question 30

What might the uncontrolled reduction in the rate of the cell cycle result in?

Answer 30

Degenerative diseases such as Alzheimer’s.

Question 31

What might the uncontrolled increase in the rate of the cell cycle result in?

Answer 31

The formation of a tumour.

Question 32

What is a proto - oncogene?

Answer 32

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 33

What is apoptosis?

Answer 33

Apoptosis is the death of cells which occurs as a normal and controlled part of an organism’s growth or development (programmed cell death).

Question 34

How is apoptosis triggered?

Answer 34

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

Question 35

Why is the production of death signalling molecules from lymphocytes an example of?

Answer 35

The production of death signal molecules from lymphocytes is an example of an external death signal. The death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm.

Question 36

What is DNA damage an example of?

Answer 36

Internal death

Question 37

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

Answer 37

Activation of p53 tumour - suppressor protein.

Question 38

What do both internal and external death signals result in?

Answer 38

The activation of caspases (types of protease enzyme) that cause the destruction of the cell.

Question 39

Why is apoptosis essential during the development of an organism?

Answer 39

To remove cells no longer required as development progresses or during metamorphosis.

Question 40

What might cells initiate apoptosis in the absence of?

Answer 40

Growth factors