Cell Cycle Flashcards
(25 cards)
What is the purpose of the cell cycle?
Enable a cell to grow to maturity
So an organism can maintain certain number of cells
To replace lost or damaged cells
How do prokaryotes divide?
Binary fission - DNA attaches to membrane, cell and DNA then enlarge and septum forms down centre of cell
How does prokaryotic replication occur?
Two replication forks form at origin (ori) of circular DNA and then two identical copies of the original DNA will have been created
How does prokaryotic cytokinesis occur?
The protein, ftsZ, is dispersed across cell during cytokinesis, this collects in centre of cell and cuts cell in half
Why is prokaryotic replication multi-forked?
Replication ad cytokinesis must be coordinated, but cell division takes much less time
Multi-forked replication means at least one replication will be finished in time for cytokinesis
What are the complications with eukaryotic replication?
There are multiple linear chromosomes, multiple organelles and different types of cells depending on the tissue
What are the stages of interphase?
G1 - growth phase, doubling mass of everything
S - DNA synthesis phase, chromosome duplication
G2 - preparation for mitosis
M - mitosis, main events: nuclear division and cytokinesis
What is responsible for making sure sister chromatids stay near each other after S phase and when is it broken?
Cohesin which joins around the centre of both chromatids and kleisin holds the circle of cohesin together
A protease cleaves kleisin just before cytokinesis
What makes chromatids really compact?
Condensin which circles loops of DNA and compacts them tightly
How does mitotic spindle form?
Nuclear membrane breaks down and the chromatin comes from the spindle pole bodies
They contain kinetochore which binds to the centromere of the chromosomes
What happens during cytokinesis?
Nuclear membrane begins to reform as a contractile ring formed of actin and myosin II pinches the cell in two from the outside in
In plants their cell wall forms inside out
Why are early embryonic cell cycles faster than somatic cell cycles?
They divide without growth
What is special about the first division of a c.elegans egg?
The first division is asymmetric, as protein which drives formation of germ cells is all on one side
What do niche cells?
Stem cells are bound to niche cells which stop them from differentiating but allow them to divide, one daughter cell is unattached and is free to differentiate while the other will stay with niche cell
What is anchorage dependence?
Cells must be attached to a substratum in order to divide
What is density-dependent inhibition?
Cells stop dividing when in contact with another cell
What is the cell cycle control system?
Cell cycle engine - protein complex that drives cycle
Co-ordination - replicated DNA must go through mitosis before it can start again
Checkpoints - cell cycle will stop if cell is deprived of nutrients or something is damaged
What protein drives the cell cycle?
Cyclin dependent protein kinase, levels of the kinase stay the same for the whole cycle but the activity of the kinase changes
Why are cyclins important to regulating the cell cycle?
They interact with CDK and undergo cycles of synthesis and degradation so their levels change
There are different cyclin and kinase pairs for different parts of the cell cycle
What pairs together for G1/S phase?
Cyclin E and G1/S CDK
What pairs together for M phase?
Cyclin B and M CDK
What does mitotic CDK do?
It breaks down the nuclear lamina that holds together the nuclear membrane
What happens if an S stage cell is fused with a G1 or G2 stage cell?
An S stage cell will force a G1 cell into S stage but not a G2 stage cell
What types of checkpoints prevent the cell cycle from continuing?
R point - a growth factor from outside will instruct a cell to divide
At G2/M DNA synthesis must be complete or cell cycle will be suspended
Chromosomes must all be attached to spindle fibres
DNA repair watch occurs throughout
