Unit 1 - Protein Control of Cell Division

Question 1

What is the cytoskeleton?

Answer 1

Complex network of protein filaments that gives mechanical support and shape to cells.

Question 2

What does the cytoskeleton consist of?

Answer 2

Different protein structures, including microtubules, which are found in all eukaryotic cells.

Question 3

What are microtubules?

Answer 3

Hollow cylinders composed of the protein tubulin.

Question 4

What do microtubules radiate from?

Answer 4

The microtubule organising centre (MTOC) or centrosome.

Question 5

What do microtubules control?

Answer 5

The movement of membrane-bound organelles and chromosomes. Also form the spindle fibres that are active during cell division.

Question 6

What does the formation and breakdown of microtubules involve?

Answer 6

Polymerisation and depolymerisation of tubulin.

Question 7

What requires remodelling of the cytoskeleton?

Answer 7

Cell division.

Question 8

What are the two main phases that the cell cycle consists of?

Answer 8

Interphase and mitotic phase.

Question 9

What are the phases of interphase?

Answer 9

G1 - growth phase
S - phase where DNA is replicated
G2 - growth phase

Question 10

What are the two processes in the mitotic phase?

Answer 10

Mitosis and cytokinesis.

Question 11

What is mitosis?

Answer 11

Separation of chromosomal material by the spindle microtubules.

Question 12

What is cytokinesis?

Answer 12

Separation of the cytoplasm into two daughter cells.

Question 13

What are the 4 phases of mitosis?

Answer 13

Prophase,
Metaphase,
Anaphase,
Telophase

Question 14

Describe prophase.

Answer 14

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 the chromosomes via their kinetochores in the centromere region.

Question 15

Describe metaphase.

Answer 15

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

Question 16

Describe anaphase.

Answer 16

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

Question 17

Describe telophase.

Answer 17

The chromosomes condense and nuclear membranes are formed around them.

Question 18

What is progression through the cell cycle controlled by?

Answer 18

Checkpoints.

Question 19

What are checkpoints?

Answer 19

Mechanisms within the cell that assess the conditions of the cell during the cell cycle and halt progression to the next phase until certain requirements are met.

Question 20

What are the proteins that accumulate during cell growth and are involved in regulating the cell cycle?

Answer 20

Cyclin proteins.

Question 21

What is the order of the cell cycle?

Answer 21

G1
S
G2
M

Question 22

What do cyclins combine with and activate?

Answer 22

Cyclin-dependent kinases (CDKs)

Question 23

What do active cyclin-CDK complexes do?

Answer 23

Phosphorylate proteins that regulate progression through the cell cycle.

Question 24

Where are the checkpoints in the cell cycle?

Answer 24

G1, G2, Metaphase

Question 25

What happens at the G1 checkpoint?

Answer 25

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 so cells progress from G1 to S.

Question 26

What happens at the G2 checkpoint?

Answer 26

The success of DNA replication and any damage to DNA is assessed.
DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death. If this checkpoint passes, the cell progresses from G2 to M phase.

Question 27

What happens at the metaphase checkpoint?

Answer 27

The M checkpoint controls progression of metaphase to anaphase. Progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.

Question 28

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

Answer 28

May result in degenerative diseases.

Question 29

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

Answer 29

May result in tumour formation.

Question 30

What is a proto-oncogene?

Answer 30

A normal cell, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene.

Question 31

What is apoptosis?

Answer 31

Programmed cell death.

Question 32

What is apoptosis triggered by?

Answer 32

Cell death signals that can be internal or external.

Question 33

Give an example of an external death signal and explain what happens.

Answer 33

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

Question 34

Give an example of an internal death signal and explain what happens.

Answer 34

DNA damage.

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

Question 35

What do both types of death signal result in the activation of that cause the destruction of the cell?

Answer 35

Caspases (types of protease enzyme).

Question 36

Why is apoptosis essential during development of an organism?

Answer 36

Removes cells that are no longer required as development progresses or during metamorphosis.

Question 37

What might cells initiate apoptosis in the absence of?

Answer 37

Growth factors.