Unit 1 - Protein control of cell division

Question 1

What does the cytoskeleton do?

Answer 1

The cytoskeleton gives mechanical support
and shape to cell

Question 2

What does the cytoskeleton consist of?

Answer 2

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

Question 3

What are microtubules?

Answer 3

Microtubules are hollow cylinders composed
of the protein tubulin

Question 4

What doe microtubules radiate from?

Answer 4

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

Question 5

What is the function of microtubules?

Answer 5

Microtubules control the movement of
membrane-bound organelles and
chromosomes

Question 6

What does the formation and breakdown of microtubules involve?

Answer 6

involves polymerisation and depolymerisation
of tubulin

Question 7

What do microtubules form?

Answer 7

Microtubules form the spindle fibres that are
active during cell division

Question 8

What are the two phases of the cell cycle?

Answer 8

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

Question 9

What does interphase involve?

Answer 9

Interphase involves growth and DNA
synthesis

Question 10

What does the G1 phase involve?

Answer 10

a growth phase

Question 11

What does the S phase involve?

Answer 11

during which the DNA is replicated

Question 12

What does the G2 phase involve?

Answer 12

a further growth phase

Question 13

What are the three sub phases of interphase?

Answer 13

G1, S, G2

Question 14

What happens during the mitotic phase?

Answer 14

In mitosis the chromosomal material is separated by the spindle microtubules. This is followed by cytokinesis,

Question 15

What does cytokinesis involve?

Answer 15

in which the
cytoplasm is separated into two daughter
cells

Question 16

What are the four phases of mitosis?

Answer 16

Prophase, Metaphase, Anaphase and Telophase

Question 17

What happens during Prophase?

Answer 17

• 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 18

What happens during metaphase?

Answer 18

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

Question 19

What happens during anaphase?

Answer 19

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

Question 20

What happens during telophase?

Answer 20

The chromosomes decondense and the nuclear membranes are formed around them.

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 cyclin proteins?

Answer 22

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

Question 23

What do cyclins combine with to form

Answer 23

Cyclins combine with and activate cyclin-dependent kinases (CDKs)

Question 24

What do active CDK complexes do?

Answer 24

phosphorylate proteins that regulate progression through the cycle

Question 25

What happen if sufficient phosphorylation is reached?

Answer 25

progression occurs

Question 26

What happens at the G1 checkpoint?

Answer 26

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 27

What is Retinoblastoma?

Answer 27

(Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication

Question 28

What happens during G2 checkpoint?

Answer 28

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

Question 29

What happens when DNA is damaged during G2 checkpoint?

Answer 29

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

Question 30

What does the metaphase checkpoint do?

Answer 30

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 31

What happens is there is an uncontrolled reduction in the rate of the cell cycle?

Answer 31

may result in degenerative disease

Question 32

What happens if there is an uncontrolled increase in the rate of the cell cycle?

Answer 32

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

Question 33

What is a proto-onco gene?

Answer 33

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

Question 34

What can happen to a proto-onco gene?

Answer 34

which can mutate to form a tumour-promoting oncogene

Question 35

What is apoptosis triggered by?

Answer 35

cell death signals that can be external or internal

Question 36

What is an example of an external death signal?

Answer 36

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

Question 37

What is an example of an internal death signal?

Answer 37

DNA damage is an example of an internal death signal

Question 38

What do external death signals do?

Answer 38

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

Question 39

What do internal death signals cause?

Answer 39

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

Question 40

What do both death signals result in?

Answer 40

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

Question 41

Why is apoptosis essential?

Answer 41

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

Question 42

Why might cells initiate apoptosis?

Answer 42

in the absence of growth factors