Unit 1: Key Area 5 - Protein control of cell division

Question 1

What is the function of cytoskeleton within a cell

Answer 1

The cytoskeleton gives mechanical support and shape to cells

Question 2

Describe the structure of cytoskeleton

Answer 2

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

Question 3

Describe the structure of microtubules and where they radiate from

Answer 3

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

Question 4

What is the function of microtubules

Answer 4

Microtubules control the movement of membrane-bound organelles and chromosomes

Question 5

What does cell division require

Answer 5

Cell division requires remodelling of the cytoskeleton

Question 6

What does the formation and breakdown of microtubules require

Answer 6

Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin

Question 7

What do microtubules form during cell division

Answer 7

Microtubules form the spindle fibres that are active during cell division

Question 8

What does the cell cycle consist of

Answer 8

The cell cycle consists of interphase and mitotic (M) phase

Question 9

Describe interphase

Answer 9

Interphase involves growth and DNA synthesis including G1, a growth phase; S phase, during which the DNA is replicated; and G2, a further growth phase

Question 10

What does mitotic phase include

Answer 10

Mitotic phase involves mitosis and cytokinesis

Question 11

Describe what happens during mitosis and cytokinesis

Answer 11

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 12

What does mitosis consist of

Answer 12

Mitosis consists of prophase, metaphase, anaphase and telophase

Question 13

Describe prophase

Answer 13

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 14

Describe Metaphase

Answer 14

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

Question 15

Describe Anaphase

Answer 15

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

Question 16

Describe Telophase

Answer 16

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

Question 17

How is progression through the cell cycle controlled

Answer 17

Progression through the cell cycle is controlled by checkpoints

Question 18

Describe what checkpoints are

Answer 18

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 19

What do cyclin proteins do

Answer 19

Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle
Cyclins combine with and activate cyclindependent kinases (CDKs). Active cyclinCDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.

Question 20

Describe what happens at the G1 checkpoint

- What does Phosphorylation by G1 cyclin-CDK do and what is the result of this

Answer 20

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 21

Describe the metaphase checkpoint

Answer 21

A 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 22

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

Answer 22

An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease

Question 23

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

Answer 23

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

Question 24

What is a proto-oncogene and what is it usually involved in

Answer 24

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 25

What triggers apoptosis

Answer 25

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

Question 26

Give an example of external death signal

Answer 26

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

Question 27

Give an example of internal death signal

Answer 27

DNA damage is an example of an internal death signal.

Question 28

Describe an external death signal

Answer 28

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

Question 29

Describe an internal death signal

Answer 29

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

Question 30

Describe what happens as a result of both external and internal death signal

Answer 30

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

Question 31

When is apoptossis essential and why

Answer 31

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

Question 32

When may cells initiate apoptosis

Answer 32

Cells may initiate apoptosis in the absence of growth factors