UNIT 1 - control of the cell cycle

Question 1

what is the cytoskeleton made of and what is the function of it?

Answer 1

a microscopic network of actin filaments and tubules in the cytoplasm of many living cells that supports their shape and function

Question 2

what are microtubules and what is their function?

Answer 2

Microtubules are hollow cylinders, composed of the protein tubulins, which radiate from the microtubule organising centre (MTOC), or centrosome.

Microtubules control the movement of membrane-bound organelles and chromosomes

Question 3

what does cell division require?

Answer 3

Cell division requires remodelling of the cytoskeleton.

Question 4

what does the formation and breakdown of microtubules involve?

Answer 4

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

Question 5

what do microtubules form during cell division?

Answer 5

Microtubules form the spindle fibres that are active during cell division

Question 6

what are the two phases in the cell cycle?

Answer 6

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

Question 7

what are the steps of interphase?

Answer 7

Interphase involves growth and DNA synthesis including:

a) G1, a growth phase
b) S, a phase during which the DNA is replicated
c) G2, a further growth phase.

Question 8

what does the mitotic phase involve?

Answer 8

The mitotic phase involves mitosis and cytokinesis. 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 9

what are the stages of mitosis?

Answer 9

Mitosis consists of prophase, metaphase, anaphase and telophase.

Question 10

what happens in prophase? (mitosis)

Answer 10

In prophase, DNA condenses into chromosomes, each consisting of two sister chromatids; the nuclear membrane breaks down, and spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region.

Question 11

what happens in metaphase? (mitosis)

Answer 11

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

Question 12

what happens in anaphase? (mitosis)

Answer 12

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

Question 13

what happens in telophase? (mitosis)

Answer 13

In telophase, the chromosomes decondense and nuclear membranes are formed around them.

Question 14

what are cell checkpoints and their function?

Answer 14

Progression through the cell cycle is controlled by cell cycle checkpoints, which are mechanisms within the cell that assesses the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met.

Question 15

what do cyclin proteins do in the cell cycle?

Answer 15

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

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

Active cyclin-CDK complexes phosphorylate proteins that regulate progression through the cycle. if sufficient phosphorylation is reached, progression occurs.

Question 16

what happens at the G1 checkpoint?

Answer 16

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 17

what does phosphorylation by G1 cyclin-CDK do in G1?

Answer 17

Phosphorylation by G1 cyclin-CDK inhibits Rb. Inhibition of Rb allows transcription of the genes that code for proteins needed for DNA replication and cells progress from G1 to S phase.

Question 18

what happens at the G2 checkpoint?

Answer 18

At the G2 checkpoint, 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

Question 19

what happens in metaphase checkpoint?

Answer 19

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 20

what are uncontrolled rate of the cell cycle cause?

Answer 20

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

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

Question 21

what is a proto-oncogene?

Answer 21

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

Question 22

what is apoptosis?

Answer 22

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

Question 23

what is an example of an external death signal?

Answer 23

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

Question 24

what do external and internal death signal molecules do?

Answer 24

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

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

Both types of death signals result in the activation of caspase cascades, which cause the destruction of the cell.

Question 25

when is apoptosis essential?

Answer 25

Apoptosis is essential during the development of an organism to remove cells that are no longer
required as development progress or during metamorphosis.

Cells may initiate apoptosis in the absence of growth factors.

Question 26

what is a caspase cascade?

Answer 26

protease enzymes involved in a series of reactions (a cascade) that destroy a cell

Question 27

what is the cell cycle?

Answer 27

a four-stage process in which the cell increases in size (G1 stage), copies its DNA (S stage), prepares to divide (G2 stage) and divides by mitosis (M stage)

Question 28

what are cell cycle checkpoints?

Answer 28

checkpoints during G1, G2 and metaphase that assess the readiness of a cell to enter the next stage of the cell cycle

Question 29

centromere meaning?

Answer 29

the specialised DNA sequence of a chromosome that links a pair of sister chromatids

Question 30

definition of cyclic proteins?

Answer 30

proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes

Question 31

what are kinetochores?

Answer 31

a complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach

Question 32

what is metamorphosis?

Answer 32

a process that involves a significant change in an organism’s physical form during development

Question 33

what is the microtubule organising centre? (MTOC)

Answer 33

structure found in eukaryotic cells from which microtubules are produced for the formation of the spindle fibres

Question 34

mitosis definition>

Answer 34

a division of the nucleus to form two new nuclei, each with a full complement of chromosomes

Question 35

what is P53?

Answer 35

a tumour-suppressor protein that can stimulate DNA repair, arrest the cell cycle or cause cell death (apoptosis) by the activation of caspases