Key Area 5 - Protein Control of Cell Devision

Question 1

Protein Control of Cell Division

Question 2

The Cytoskeleton and Cell Division

Question 3

What does the cytoskeleton consist of?

Answer 3

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

Question 3

What does the cytoskeleton give?

Answer 3

The cytoskeleton gives mechanical support
and shape to cells.

Question 4

What are microtubules?

Answer 4

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

Question 5

What do microtubules control?

Answer 5

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

Question 6

What does cell division require?

Answer 6

Cell division requires remodelling of the
cytoskeleton.

Question 7

What does formation and breakdown of microtubules involve?

Answer 7

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

Question 8

What do microtubules form?

Answer 8

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

Question 9

The Cell Cycle

Question 10

What does the cell cycle consist of?

Answer 10

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

Question 11

What does interphase involve?

Answer 11

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 12

What does the mitotic phase involve?

Answer 12

Mitotic phase involves mitosis and
cytokinesis.

Question 13

What happens during mitosis?

Answer 13

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 14

Mitosis consists of what?

Answer 14

Mitosis consists of prophase, metaphase,
anaphase and telophase.

Question 15

Explain what happens during Prophase:

Answer 15

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 16

Explain what happens during Metaphase:

Answer 16

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

Question 17

Explain what happens during Anaphase:

Answer 17

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

Question 18

Explain what happens during Telophase:

Answer 18

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

Question 19

Control of the Cell Cycle

Question 20

Progression through the cell cycle is
controlled by what?

Answer 20

Progression through the cell cycle is
controlled by checkpoints.

Question 21

What are checkpoints?

Answer 21

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 22

What are involved in regulating the cell
cycle?

Answer 22

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

Question 23

What do cyclins combine with and activate? What does this lead to?

Answer 23

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

Question 24

At G1, what occurs?

Answer 24

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 25

What does phosphorylation by G1 cyclin-CDK inhibit?

Answer 25

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

Question 26

Inhabitation of Rb allows what to happen?

Answer 26

This allows transcription of the genes that
code for proteins needed for DNA replication.

Cells progress from G1 to S phase.

Question 27

At G2, what occurs?

Answer 27

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

Question 28

What does DNA damage trigger?

Answer 28

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

Question 29

A metaphase checkpoint controls what?

Answer 29

A metaphase checkpoint controls
progression from metaphase to anaphase.

Question 30

Explain what happens at the metaphase checkpoint:

Answer 30

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

Question 31

An uncontrolled reduction in the rate of the cell cycle may result in what?

Answer 31

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

Question 32

An uncontrolled increase in the rate of the
cell cycle may result in what?

Answer 32

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

Question 33

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

Answer 33

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 34

Control of Programmed Cell Death
(Apoptosis)

Question 35

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

Answer 35

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

DNA damage is an example of an internal death signal.

Question 36

Apoptosis is triggered by what?

Answer 36

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

Question 37

Binding of an external death signal molecule to a surface receptor protein triggers what?

Answer 37

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

Question 38

When and why is apoptosis essential?

Answer 38

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

Question 38

An internal death signal resulting from DNA damage causes what?

Answer 38

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

Question 39

What do both types of death signals result in?

Answer 39

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

Question 40

When may cells initiate apoptosis?

Answer 40

Cells may initiate apoptosis in the absence of growth factors.