28 Flashcards
What are the 4 stages of the cell cycle?
G1 phase
S phase
G2 phase
M phase
What does āGā mean?
Gap
What happens in s phase?
The cell replicates DNA once and only once
What happens in M phase?
The cell separates the chromosomes an segregates them equally
What are the key events of the M phase?
Nuclear breakdown
Chromosome condensation
Creation of the mitotic spindle
Ordered movement of chromosomes
What is kinetochore?
Specialised complex of proteins where spindle MT attach to chromosomes
What are asters?
Important in binding the microtubules that bind the chromosome and will stabilise the cell
What happens in cytokinesis/
Creation of two new cells
Partitioning of the two nuclei and organelles
Usually symmetrical division
(Stem cells divide asymmetrically)
What are the two molecules that are involved in cell regulation at the two check points?
Cyclin
Cyclin - dependent kinase (Cdk)
What are the 4 key concepts of Cdks?
Cyclical activation and inactivation of this family of enzymes controls the cell cycle
These enzymes are kinases that are regulated by a subunit called a cyclin whose levels vary
Control of degradation of these regulatory subunits is very important
CDKs phosphorylate proteins that are involved in key cell cycle events - both structural and functional
What regulates the activity of CDKs?
Phosphorylation and dephosphorylation
What does the enzyme phosphatease do?
Takes away the inhibitory phosphate
What does ubiquitin do?
Adding ubiquitin to proteins targets those proteins for rapid degradation
What are the 3 types of cyclin and what do they do?
S cyclins
Activate CDKs just prior to S phase
M cyclins
Activate CDKs and regulate entry into mitosis
G1/S cyclins
Activate CDKs in late G1
What conditions in G1 would not allow the cell cycle to continue?
Damaged DNA
Unfavourable extracellular environment
What conditions in S would not allow the cell cycle to continue?
Damaged or incompletely replicated DNA
What conditions in G2 would not allow the cell cycle to continue?
Damaged or incompletely replicated DNA
What conditions in M would not allow the cell cycle to continue?
Chromosomes are improperly attached to mitotic spindle
What is p53?
A key protein in the responses of cells to DNA damage
It is mutated in most human cancers when this process is deranged
How do external signals regulate cell growth?
The availability of transmembrane growth factors receptors and extracellular growth factors can increase synthesis and enhance degradation of regulatory molecules
What is a mitogen?
A substane that induces or stimulates mitosis
What happens in the absence of mitogens?
Rb protein is dephosphorylated and active
This keeps a series of transcription factors in an inactive state
whose target genes are needed for cell proliferation
What is Rb?
A key growth regulatory - mutations in Rb gene lead to abnormal Rb protein and abnormal cell cycle control
