Week 4 - Cell cycle Flashcards
Prophase
Chromatin condensation
Nucleolus disappears
Centrioles move to poles
Pro-metaphase
Nuclear membrane dissolves
Chromosomes attach to microtubules and begin moving
Metaphase
Spindle fibres align the chromosomes along the middle of the cell nucleus (metaphase plate)
Anaphase
Paired chromosomes separate and move to opposite sides of the cell
Telophase
Chromatids arrive at the opposite poles of cell
New membranes form around daughter nuclei
Chromosomes decondense
Spindle fibres disperse
How long roughly does the entire cell cycle take
24 hours
4 things that happen during G1 phase
Growing in size
Monitoring development
RNA and protein synthesis in preparation for S phase
Growth-factor dependent
3 things that happen during G2 phase
Further growth
Cell organelle replication
Preparation for mitosis
What happens during S phase
Synthesis of DNA
What is another name for G0 phase and give an example of a cell like this
Quiescent e.g erythrocyte
What is the role of cyclin-dependent kinases
Regulate the progression through the cell cycle
What else can CDKs be dependent on? (I think)
Cyclins
Phosphorylation/dephosphorylation
CKIs
Which CDK and cyclin at end of G1
CDK4/6-cyclin D
Which CDK and cyclin during S
CDK2-cyclin E
Which CDK and cyclin between S and M
CDK2 - cyclin A
Which CDK and cyclin at end of G2 and mainly during mitosis
CDK1-cyclin B
3 families of CDK inhibitors
p21 CIP
p27 KIP
p16 INK
How do CDK inhibitors work
by forming an inactive complex or by acting as a competitive CDK ligand
What else is cyclin B/CDK1 known as
Maturation promoting factor
Which cyclin level starts to increase during G2
Cyclin B
What does maturation promoting factor do
It breaks down the nuclear envelope (breaks down the lamina)
Condenses chromosomes
Forms spindles (microtubule-associated proteins)
Where are the 4 checkpoints on the cell cycle and what does each do
Restriction point (G1) - checks for cell size and favourable environmental conditions
DNA damage checkpoints (late G1 and G2) - checks for DNA damage before replication (G1) and checks for damaged or unduplicated DNA (G2)
Metaphase checkpoint - checks for chromosome attachment to mitotic spindle
Cell cycle progression is determined by the presence of which factors
Growth factors
What is the restriction factor
The point in which the cell no longer requires growth factors to complete the cell cycle and commits to cell division
Which cyclin is required for progression from G1 to restriction point
Cyclin D
How long before initiation of S phase is cyclin D
2-3 hours before
Which protein acts as a gatekeeper at the restriction point
Retinoblastoma (Rb) protein
What is epidermal growth factor involved in (EGF)
Re-epithelialisation
What is platelet derived growth factor (PDGF)
Matrix formation (>fibroblasts+migration) and remodelling (production of proteases)
Vascular endothelial growth factor
Angiogenesis (endothelial cell>+migration)
What happens when growth factor increases at restriction point
Growth factor activates CDK-Cyclin 4/6D
This causes phosphorylation of Rb protein which stops the inhibition of the transcription factor E2F
Gene transcription occurs
mRNA translation occurs
Enzymes and other proteins are produced that are involved in S phase
What do tumour supressor genes do?
They act as the ‘brakes of the cell; they encode cell proteins that inhibit cell growth and proliferation to maintain the integrity of the genome
This causes cell cycle arrest in abnormally dividing cells and repair DNA damage
3 examples of tumour suppressors
Rb –> blocks entry to mitosis
p53 –> detects DNA damage
BRCA1 –> DNA repair
What can cause damage to DNA
Chemical mutagens, radiation, errors in replication
Rb =
blocks entry to M
p53 =
detects DNA damage
What type of factor is p53
A transcription factor
What does p53 do
Inhibits cell cycle progression if DNA damage has occurred, which can cause cell cycle arrest and then apoptosis OR DNA repair
If levels of p53 is too low which other tumour suppressor does this causes the expression of
p21
Which checkpoints involve p53/23
Late G1 and late G2
What happens at the spindle assembly checkpoint
Checks whether chromosomes are attached to the spindle
What happens if chromosomes aren’t attached to spindles
Anaphase is inhibited, anaphase promoting complex is inhibited until all chromosomes are attached, once they are, anaphase inhibition is alleviated
