Cell Cycle Control

Question 1

Physical mechanisms that are involved in control of the cell cycle

Answer 1

Anchorage dependence- they must be in contact with a solid surface
Density-dependent inhibition- crowded cells stop dividing. Animal cells stop dividing when they touch each other

Question 2

Outline an M-phase inducer

Answer 2

Can drive cells earlier in the cell cycle to enter mitosis

Question 3

Outline an s-phase inducer

Answer 3

Drives G1 to enter S phase

Question 4

Outline G2 main driver

Answer 4

Doesn’t go backwards and re-replicate cells

Question 5

Outline the discovery of maturation promoting factor

Answer 5

-cytoplasm taken from mature oocyte & injected into G2 immature oocyte induces oocyte to enter the first meiosis division. M phase
-cytoplasm taken from a variety of actively dividing cell from a range of organism could prematurely induce M phase
-MPF activity low in G2 and peaked in mitosis
-MPF was purified-n a protein with two subunits and had kinase activity

Question 6

How would i use yeast to find the genes involved in the cell cycle

Answer 6

Forward genetics and conditional mutants

Question 7

What enzyme regulates the cell cycle

Answer 7

Cyclin dependent kinase
Kinase enzyme only active when complexed with cyclin

Question 8

What enzyme regulates the cell cycle

Answer 8

Cyclin dependent kinase
Kinase enzyme only active when complexed with cyclin

Question 9

Define cyclin

Answer 9

The regulatory subunit of the dimer. Synthesised and destroyed in the cell cycle

Question 10

Define G1/S cyclin

Answer 10

Trigger progression through start, resulting in commitment to cell cycle entry

Question 11

Define S cyclin

Answer 11

Bind to CDKs soon after progression through start and help stimulate chromosome duplication

Question 12

Define M cyclin

Answer 12

Activate CDKs to stimulate entry into mitosis

Question 13

What to M CDKs do

Answer 13

M CDKs are phosphorylated to inhibit their activity by Wee1 kinase
A phosphotases (cdc25) activates the cyclin-CDK complex, which triggers mitosis

Question 14

Outline the G2/M checkpoint

Answer 14

Passing this point represents commitment to mitosis

Question 15

Outline the spindle checkpoint

Answer 15

Ensures all of the chromosomes are attached to the spindle in preparation for anaphase

Question 16

Outline the START (yeast) and restriction point (animals) checkpoint

Answer 16

Cell decides wether to divide or not

Question 17

Outline the function of anaphase promoting complex

Answer 17

Cohesin hold chromatids together, from S phase, to end of metaphase/ start of anaphase
The APC starts anaphase; it targets proteins for destruction using ubiquitin

Question 18

How is APC activated

Answer 18

-sensing system at spindle checkpoint not well understood but involves; Mad2, triggered by the presence of all chromosomes at metaphase plate and tensio on microtubules
-APC activator active only after all chromosomes attached

Question 19

What is the first role of AOC

Answer 19

Marks a protein called securin for destruction by the proteasome, by the addition of ubiquitin (when activated by the ativiting subunit)
-securin inhibits another protease called esperarse
-the release seperase destroys Cohesin

Question 20

What is the second role of APC

Answer 20

Destroy M and S cyclin by adding ubiquitin chains to the CDK

Question 21

What happens when reforming the nuclear envelope

Answer 21

-in prophase, M-cyclin phosphorylated lamins, so the nuclear envelope breaks down
-after M cyclin destroyed, ‘lamins’ lose their phosphate groups
-nuclear envelope to reforms around each set of chromosomes

Question 22

Define mitogens

Answer 22

Stimulate cell division primarily by overcoming intracellular breaking mechanisms

Question 23

Define growth factor

Answer 23

Stimulate cell growth (increase in size and mass)

Question 24

Which part of the cell cycle is resceptible to growth factors

Answer 24

Restriction point

Question 25

How does the signal get to the mitogen to make it divide

Answer 25

Cells have the receptor mitogen on them, a signal pathway including MAP activates G1/S-Cdk by phosphorylation Activated G1/S-Cdk phosphorylated Rb, which releases/activates E2F transcription regulators The released transcription regulators activate transcription of genes that allow the cell to progress through the restriction point

Question 26

Outline the origin of replication complex

Answer 26

PreRC (includes DNA helicase) bind to the origins of replication complex at the origins of replication Once replication starts, pre-replication complex is destroyed, but not the origin of replication complex.

Question 27

What is the role of S-cyclin

Answer 27

-S-CDKs activates DNA helicase in preRC to initiate DNA replication -S-CDKs prevents assembly of new preRCs -Activation of anaphase promoting complex targets S cyclin for destruction during mitosis, allowing the preRC to reform

Question 28

Outline the discovery of P53

Answer 28

Protein-bound to p53- from a virus made cells never die

Question 29

Roles of active p53 following DNA damage

Answer 29

DNA damage and telomere shortening activates p53, turns on DNA repair, activates P21, turns on apoptosis pathway

Question 30

What is p53s response to DNA damage

Answer 30

P53 is phosphorylated, which is active and stable P53 is a transcription factor, and binds to the regulatory region of the p21 gene leading to transcription of p21 P21 activates G1/S-Cdk and S-Cdk

Question 31

What happens to P53 gene with a deleterious mutation

Answer 31

G1/S and M-CDKs are still active P21, repair and apoptosis not activated

Question 32

Name types of genes, that when mutated can lead to cancer

Answer 32

Proto-oncogenes Tumour suppressors

Question 33

Define pronto-oncogenes

Answer 33

A gene which codes for proteins often involved in signal transduction from mitogens -when a mutation permanently activates the gene turn into oncogenes

Question 34

Define tumour suppressors

Answer 34

Or anti-oncogene, is a gene that regulates the cells response to damage. When mutated, cells divide despite damage to DNA