the Cell Cycle Flashcards
what is the G0 phase (quiescence)
the phase when cells are not actively dividing. this is not always permanent, the cells can re enter from Go.
roughly how long does it take a cell to complete the cell cycle?
one day generally
generally how long is G1?
11 hours
generally how long is S?
8 hours
generally how long is G2?
4 hours
generally how long is M?
1 hour
what does interphase consist of?
G1, S, G2
what does the M phase consist of?
Mitosis, Cytokinesis
what is interphase?
the parts of the cell cycle involved in growth and preparation for cell division
what happens during S phase?
synthesis of DNA creating chromosomes now consist of two sister chromatids
What happens during G1?
growing in size
monitoring environment for appropriate conditions for cell division
RNA & protein synthesis in prep for S phase
Growth factor dependent
what happens during G2?
further growth
cell organelle replication
preparation for mitosis
what happens during mitosis?
the cells separate the chromosomes
what is cytokinesis?
the cytoplasm is divided into two daughter cells, completing the cell cycle
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 oposite sides of the cell
telophase
chromatids arrive at the opposite poles of the cell
new membranes form around daughter nuclei
chromosomes decondense
spindle fibres disperse
what are CDK’s (cyclin dependent kinases)
they regulate the progression through the cell cycle
how are CDK’s regulated
cyclins, phosphorylation and dephosphorylation and CKI’s
what are cyclins?
small short lit proteins which must be associated with the cdk for it to be active
what activates CDK 4/6 (G1) ?
cyclin D
what activates CDK2?
cyclin E (G1 to S) or cyclin A (S to Metaphase)
what activates CDK1 (G2 to Anaphase) ?
cyclin B
What are CKI’s?
cyclin dependent kinase inhibitors. they are small proteins that block cyclin activity either by forming an inactive complex or by acting as a CDK ligand.
what are the three families of CKID’s?
p21 CIP
p27 KIP
p16 INK
what is MPF (maturation promoting factor)?
cdk1/ cyclin B
what do kinases do?
they phosphorylate things
what does MPF phosphorylate that results in entry to M phase?
-phosphorylate lamins results in nuclear envelope being destroyed
-phosphorylates condensins histones which results in chromosome condensation
- phosphorylates microtubule associated proteins (MAP’s) which results in spindle formation
which cyclin is required for passage through the restriction point (G1) ?
cyclin D
where is the restriction point?
G1
where is the DNA damage checkpoints?
late G1 and G2
what happens at the restriction point checkpoint?
checks for cell size and favourable environmental conditions
what happens at the DNA damage checkpoints?
- check for DNA damage
- check for damaged or unduplicated DNA
what happens at the M checkpoint?
checks for chromosome attachment to mitotic spindle
what is RB?
a protein which acts as the gatekeeper at the restriction point . it inhibits E2F (a transcription factor) when there is no growth factor present. once there is enough CDK4/6 cyclin D made it phosphorylates Rb which unbinds from transcription factor which then allows for transcription of genes for progression to s phase
what does p53 do?
it is a transcription factor that detects damage to DNA which results in the production of cyclin dependent kinase inhibitors p21 so that DNA repair can take place. can also promote apoptosis.
what are tumour suppressor genes?
encode normal cell proteins that inhibit cell proliferation and growth of cell to maintain the integrity of the genome. they cause cell cycle arrest in abnormally dividing cells and repair DNA damage. Eg the bakes of the cell cycle
what happens at the spindle assembly checkpoint?
if the chromosomes are unnattatched the checkpoint is on and anaphase is inhibited. once all chromosomes are attached the inhibition of anaphase is alleviated. APC is inhibited until all chromosomes are attached.
Which cyclins are regulated by mitogens
Cyclin D
