biology - 1.5

Question 1

What does the cytoskeleton give?

Answer 1

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

Where do microtubules radiate from?

Answer 4

The microtubule organising centre (MTOC) or centrosome.

Question 5

What do microtubules do?

Answer 5

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

Question 6

What does cell division require?

Answer 6

Remodelling of the cytoskeleton.

Question 7

What does formation and breakdown of microtubules involve?

Answer 7

Polymerisation and depolymerisation of tubulin.

Question 8

What do microtubules form?

Answer 8

The spindle fibres that are active during cell division.

Question 9

What does the cell cycle consist of?

Answer 9

Interphase and mitotic (M) phase.

Question 10

What does interphase involve?

Answer 10

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

Question 11

What does mitotic phase involve?

Answer 11

Mitosis and cytokinesis.

Question 12

In mitosis, how is the chromosomal material separated?

Answer 12

By the spindle microtubules.

Question 13

What happens in cytokinesis, which follows mitosis?

Answer 13

The cytoplasm is separated into two daughter cells.

Question 14

What does mitosis contain?

Answer 14

Prophase, metaphase, anaphase and telophase.

Question 15

What happens in prophase?

Answer 15

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

What happens in metaphase?

Answer 16

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

Question 17

What happens in anaphase?

Answer 17

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

Question 18

What happens in telophase?

Answer 18

The chromosomes decondense and nuclear membranes are formed around them.

Question 19

How is the progression through the cell cycle controlled?

Answer 19

By checkpoints.

Question 20

What are checkpoints?

Answer 20

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 involved in regulating the cell cycle?

Answer 21

Cyclin proteins that accumulate during cell growth.

Question 22

What do cyclins do?

Answer 22

They combine with and activate cyclin- dependent kinases (CDKs).

Question 23

What do active cyclin-CDK complexes phosphorylate?

Answer 23

Proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.

Question 24

At the G1 checkpoint, what happens?

Answer 24

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 do?

Answer 25

Inhibits the retinoblastoma protein (Rb).

Question 26

What does inhibition of the retinoblastoma protein allow?

Answer 26

Transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.

Question 27

At the G2 checkpoint, what is assessed?

Answer 27

The success of DNA replication and any damage to DNA.

Question 28

What does DNA damage trigger?

Answer 28

The activation of several proteins including p53.

Question 29

What can p53 do?

Answer 29

It can stimulate DNA repair, arrest the cell cycle or cause cell death.

Question 30

What does a metaphase checkpoint control?

Answer 30

Progression from metaphase to anaphase.

Question 31

At the metaphase checkpoint, what happens?

Answer 31

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

Question 32

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

Answer 32

Degenerative disease.

Question 33

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

Answer 33

Tumour formation.

Question 34

What is a photo-oncogene?

Answer 34

A normal gene, usually involved in the control of cell growth or division, 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.

Question 37

What is an example of an internal death signal?

Answer 37

DNA damage.

Question 38

What do external death signal molecules bind to?

Answer 38

A surface receptor protein and trigger a protein cascade within the cytoplasm.

Question 39

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

Answer 39

Activation of p53 tumour-suppressor protein.

Question 40

What do both types of death signal result in?

Answer 40

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

Question 41

What does apoptosis do during the development of an organism?

Answer 41

It is essential as it removes cells which are no longer required as development progresses or during metamorphosis.

Question 42

When may cells initiate apoptosis?

Answer 42

In the absence of growth factors.