Topic 10 - The Cell Division Cycle Flashcards
What are the 4 phases of the cell cycle?
- M phase
- G1 phase
- S phase
- G2 phase
In simple terms, what processes occur in the M phase?
mitosis - nucleus divides
cytokinesis - cell splits in 2
In simple terms, what processes occur in the S phase?
(S = synthesis) - cell replicates nuclear DNA
What is interphase?
period between one M phase and the next (includes G1, S & G2 phases)
In simple terms, what processes occur in the G1 phase?
interval between end of M phase & start of S phase - make sure that internal and external environment conditions are suitable for S & M phases
In simple terms, what processes occur in the G2 phase?
interval between end of S phase & start of M phase - make sure that internal and external environment conditions are suitable for S & M phases
Cell - cycle control system has 3 checkpoints. what are they?
- checkpoint in mitosis - are all chromosomes properly attached to the mitotic spindle? -> pull chromosomes apart
- checkpoint in G1 - are environmental conditions favourable? -> proceed to S phase
- checkpoint in G2 - is all DNA replicated? Is all DNA damage repaired? -> proceed to M phase
The proteins of the cell-cycle control system first appeared…?
> 1 billion years ago
Which ‘switch’ mechanisms are used in the cell-cycle control system to activate/deactivate key proteins & protein complexes?
phosphorylation - protein kinases
dephosphorylation - protein phosphatases
Switching these kinases on and off at the appropriate times is partly the responsibility of another set of proteins in the control system—the …?
cyclins
The kinases of the cell-cycle control system are therefore known as
cyclin-dependent protein kinases (Cdks)
How We Know: The first components of the cell-cycle control system to be discovered were the cyclins and cyclin-dependent kinases (Cdks) that drive cells into M phase how?
Xenopus frog eggs
How We Know: M cyclin was initially identified as a protein whose concentration rose gradually during interphase and then fell rapidly to zero in which organism?
clams
Activity or levels of cyclins and cyclin-dependent kinases (Cdks) would be highest/lowest in which phase?
highest in M phase
lowest in interphase
T or F - Cyclins are regulatory subunits whose concentrations stay the same during the cell cycle
false - they vary in different cycles
Maturation Promotion Factor (MPF) = ?
cyclin-dependent protein kinases (Cdks)
Do Cdks also vary in [ ] during course of the cycle?
no - they stay constant
So what triggers the abrupt activation of these cyclin–Cdk
complexes?
For a Cdk to be active, it must be phosphorylated at one site and dephosphorylated at two other sites
The cyclin that acts in G2 to trigger entry into M phase is called …?
M cyclin
Re. THE MAJOR CYCLINS AND CDKS OF VERTEBRATES as in MCQ… which C-Cdk complex combines with which cyclin? (cyclin-A, B, D & E) put them in alphabetical order
(remember ‘small eggs’ - where these guys were initially found & studied)
S, M, G, G/S (small eggs)
A, B, D, E
Before M phase, M-Cdk phosphorylates certain certain factors. List them (think about what happens in M phase)
- Lamins -> nuclear envelope breakdown
- Nuclear pore proteins -> nuclear breakdown
- MTs -> formation of M spindles
- Histones -> DNA packing into chromatin
The Cell-Cycle Control System Also Depends on Cyclical
Proteolysis via what mechanism?
Ubiquitylation of a cyclin
When cells enter G0 phase (non-proliferating state), they can remain there for day weeks and even for the lifetime of the organism!
cool fact
Once past the G1 checkpoint, a cell usually proceeds all the way through the rest of the cell cycle quickly. In mammals, this typically takes how long?
12 - 24 hours
