1.5 b) Control of the Cell Cycle and Apoptosis

Question 1

What controls the cell cycle’s progression?

Answer 1

checkpoints

Question 2

Each event in the cell cycle must be fully completed before the __ one ___, and they must be completed in the correct ___.

Answer 2

next one begins, order

Question 3

What are checkpoints?

Answer 3

Checkpoints are mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression onto the next phase until certain requirements are met.

Question 4

Checkpoints are ___ within the cell that assess the ___ of the cell during the cell ___ and ___ progression onto the next ___ until certain ___ are met.

Answer 4

mechanisms, condition, cycle, halt, phase, requirements

Question 5

Name the proteins that accumulate during cell growth.

Answer 5

cyclins

Question 6

Cyclin proteins are involved in ___ the cell cycle.

Answer 6

regulating

Question 7

Cyclin proteins combine with and activate ____, forming ___ ___-___.

Answer 7

CDKs, active cyclin CDKs

Question 8

What do active cyclin-CKD complexes do?

Answer 8

they phosphorylate proteins that regulate progression through the cell cycle

Question 9

If sufficient ___ is reached, progression occurs.

Answer 9

phosphorylation

Question 10

Name the cell cycle’s checkpoints.

Answer 10

G1, G2, Metaphase

Question 11

What happens in the G1 checkpoint?

Answer 11

cyclin CDKs inhibit the Retinoblastoma protein (Rb) through phosphorylation (this is crucial if the S phase is to occur)

Question 12

What is the role of Rb?

Answer 12

it acts as a tumour suppressor by inhibiting the transcription of genes which code for proteins that regulate DNA replication

Question 13

What happens in the G2 checkpoint?

Answer 13

The success of DNA replication (in the S phase) is assessed, as well as any damage to DNA.

Question 14

What gets activated as a result of DNA damage?

What 3 things can the thing that got activated do?

Answer 14

several different proteins, including p53 (most importantly).

These proteins can:
a) arrest (pause) the cell cycle
b) repair the DNA
c) trigger apoptosis

Question 15

p53 gets ___ by DNA damage, and can either attempt to ___ the DNA (if damage is ___), by ‘___’ the cell cycle; or it can trigger ____ (if the damage is ___), in order to ensure no problematic ___ cells remain.

Answer 15

activated, repair, (small/light), arresting,
apoptosis, (severe), damaged

Question 16

What happens in the Metaphase checkpoint?

Answer 16

The cell cycle gets arrested until:
1. all chromosomes are correctly aligned along the metaphase plate,
2. and attached to the spindle microtubles

Question 17

Both the G1 and G2 checkpoints are to do with the _ phase of the cell cycle.

Answer 17

S (the DNA replication phase)

Question 18

The Metaphase checkpoint controls progression from ___ to ___.

Answer 18

Metaphase to Anaphase

Question 19

What causes degenerative diseases?

Answer 19

an uncontrolled decrease in the rate of the cell cycle

Question 20

What causes tumour formation?

Answer 20

an uncontrolled increase in the rate of the cell cycle

Question 21

What is an oncogene?

Answer 21

A tumour forming gene
oncology = study of cancer
oncogene = tumour forming gene

Question 22

What is a proto-oncogene?

Answer 22

a regular gene which can mutate to create a tumour-forming ‘oncogene’

Question 23

Apoptosis is triggered by ___ ___ ___, which can be ___ or ___.

Answer 23

cell death signals, internal, external

Question 24

Give an example of an internal and an external death signal.

Answer 24

internal: p53 tumour suppressor protein (activated by DNA damage)
external: death signal molecules from lymphocytes

Question 25

Both types of death signal result in the activation of ___, which are types of ___ enzyme.

Answer 25

caspases, protease

Question 26

What do caspases do?

Answer 26

Cause destruction of the cell.
Apoptosis is essentially just the activation of caspases, through internal or external signals.

Question 27

What do external death signal molecules do?

Answer 27

bind to surface receptors and trigger a protein cascade within the cytoplasm

Question 28

An internal death signal resulting from DNA damage causes activation of…

Answer 28

the p53 tumour suppressor protein

Question 29

what do the p53 and Rb proteins have in common?

Answer 29

both tumour suppressors.

p53 is activated by DNA damage, and either arrests the cycle, and repairs DNA, or triggers apoptosis. Damaged genes could create tumours - hence p53 is a tumour suppressor

Rb prevents DNA transcription and is inhibited through phosphorylation by active cyclin-CDKs

Question 30

Why is apoptosis essential during an organism’s development?

Answer 30

removes cells no longer required,
metamorphosis, (tadpole turns into frog and loses tail - apoptosis!)
or just ‘as development progresses’

Question 31

Cells may initiate apoptosis in absence of ___ ___.

Answer 31

growth factors

Question 32

Cyclins ___ during the G1 phase.

Answer 32

accumulate

Question 33

Cyclins ___ with and ___ CDKs, forming…

Answer 33

combine, activate, (active) cyclin-CDKs
CDK stands for cyclin-dependent-kinases.

Question 34

(cyclins/cyclin-CDKs) phosphorylate proteins which regulate the cell cycle.
Once sufficient ___ is reached, progression occurs.

Answer 34

cyclin-CDKs, phosphorylation.
(the k in CDKs stands for kinase, so remember that cyclins themselves don’t phosphorylate anything, they combine with CDKs and then phosphorylate proteins which regulate the cell cycle (including Rb!)

Question 35

Rb protein is inhibited during the __ checkpoint, through phosphorylation by…

Answer 35

G1, cyclin-CDKs