1.5 b) Control of the Cell Cycle and Apoptosis Flashcards
What controls the cell cycle’s progression?
checkpoints
Each event in the cell cycle must be fully completed before the __ one ___, and they must be completed in the correct ___.
next one begins, order
What are checkpoints?
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.
Checkpoints are ___ within the cell that assess the ___ of the cell during the cell ___ and ___ progression onto the next ___ until certain ___ are met.
mechanisms, condition, cycle, halt, phase, requirements
Name the proteins that accumulate during cell growth.
cyclins
Cyclin proteins are involved in ___ the cell cycle.
regulating
Cyclin proteins combine with and activate ____, forming ___ ___-___.
CDKs, active cyclin CDKs
What do active cyclin-CKD complexes do?
they phosphorylate proteins that regulate progression through the cell cycle
If sufficient ___ is reached, progression occurs.
phosphorylation
Name the cell cycle’s checkpoints.
G1, G2, Metaphase
What happens in the G1 checkpoint?
cyclin CDKs inhibit the Retinoblastoma protein (Rb) through phosphorylation (this is crucial if the S phase is to occur)
What is the role of Rb?
it acts as a tumour suppressor by inhibiting the transcription of genes which code for proteins that regulate DNA replication
What happens in the G2 checkpoint?
The success of DNA replication (in the S phase) is assessed, as well as any damage to DNA.
What gets activated as a result of DNA damage?
What 3 things can the thing that got activated do?
several different proteins, including p53 (most importantly).
These proteins can:
a) arrest (pause) the cell cycle
b) repair the DNA
c) trigger apoptosis
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.
activated, repair, (small/light), arresting,
apoptosis, (severe), damaged
What happens in the Metaphase checkpoint?
The cell cycle gets arrested until:
1. all chromosomes are correctly aligned along the metaphase plate,
2. and attached to the spindle microtubles
Both the G1 and G2 checkpoints are to do with the _ phase of the cell cycle.
S (the DNA replication phase)
The Metaphase checkpoint controls progression from ___ to ___.
Metaphase to Anaphase
What causes degenerative diseases?
an uncontrolled decrease in the rate of the cell cycle
What causes tumour formation?
an uncontrolled increase in the rate of the cell cycle
What is an oncogene?
A tumour forming gene
oncology = study of cancer
oncogene = tumour forming gene
What is a proto-oncogene?
a regular gene which can mutate to create a tumour-forming ‘oncogene’
Apoptosis is triggered by ___ ___ ___, which can be ___ or ___.
cell death signals, internal, external
Give an example of an internal and an external death signal.
internal: p53 tumour suppressor protein (activated by DNA damage)
external: death signal molecules from lymphocytes
Both types of death signal result in the activation of ___, which are types of ___ enzyme.
caspases, protease
What do caspases do?
Cause destruction of the cell.
Apoptosis is essentially just the activation of caspases, through internal or external signals.
What do external death signal molecules do?
bind to surface receptors and trigger a protein cascade within the cytoplasm
An internal death signal resulting from DNA damage causes activation of…
the p53 tumour suppressor protein
what do the p53 and Rb proteins have in common?
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
Why is apoptosis essential during an organism’s development?
removes cells no longer required,
metamorphosis, (tadpole turns into frog and loses tail - apoptosis!)
or just ‘as development progresses’
Cells may initiate apoptosis in absence of ___ ___.
growth factors
Cyclins ___ during the G1 phase.
accumulate
Cyclins ___ with and ___ CDKs, forming…
combine, activate, (active) cyclin-CDKs
CDK stands for cyclin-dependent-kinases.
(cyclins/cyclin-CDKs) phosphorylate proteins which regulate the cell cycle.
Once sufficient ___ is reached, progression occurs.
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!)
Rb protein is inhibited during the __ checkpoint, through phosphorylation by…
G1, cyclin-CDKs
