15. Mitosis Flashcards
What are the phases in the cell cycle? What happens during each phase?
What are the checkpoints in G1 that decide whether to procede with the cell cycle or not?
External signals and internal signals determine the progress of the cell cycle
Explain with detail the processes occuring in S phase of the cell cycle
(chromosome anatomy)
What are the checkpoints in G2 phase?
What are the processes in M phase? What are the stages?
P on the MAT
What are the problems associated with M phase of the cell cycle?
Explain open vs closed mitosis
Open - nuclear enevelope breaks in cell division
Closed - cell division happens inside the nuclear envelope
How is even distribution of chromosomes ensured?
Sister chromatids are matched and physically linked before division to move them together in division => ensured that chromosomes are distributed correctly - one sister chromatid in each daughter cell
How are the chromosomes moved in mitosis?
- The mitotic spindle moves the sister chromatids
- Spindle is made of filaments (microtubules)
- The mitotic spindle is assembled by the centrosomes
Explain the structure of microtubules
Microtubules - from alfa tubulin and beta tubulin dimers which polymerise into hollow tubes - microtubules are part of the cytoskeleton (involved in cell shape, transport, mitosis)
What are centrosomes made of?
- Always in pairs
- Microtubules (alpha and beta tubulin) in protein triples
How and when are centrosomes duplicated in cell cycle?
Need to duplicate to move sister chromatids into different poles - into different daughter cells
Duplicate at the same time as DNA
What are the different types of microtubules in centrosomes?
Explain the anatomy how sister chromatids are pulled by centrosomes
- kinetochores - proteins on chromatids which help K-fibers (microtubules (MT)) to stick to the chromosomes
- K-fibers (type of MT) actually move the chromatids to daughter cells
Explain the mechanism how sister chromatids are pulled by centrosomes and their possible ways
The attached K-fibers get shorter: two ways
- K-fibres shrink from the side of the kinetochore (Pac-Man)
- K-fibres shrink from the side of the spindle poles (Poleward-flux)
The two possible ways were determined: small region of tubulin in K-fiber marked - look how it moves: Pac-Man - would not move and disappear; Poleward-flux - would move towards left and disappear
Most cells use a combination of both ways to shorten K-fibres
Explain cytokinesis
In M phase
Explain the mechanism of cytokinesis
Contractile ring forms (actin and myosin components - pulling force in the ring - cell squeezed by the ring - separates into daughter cells)
What is the midbody and how it forms?
Midbody - like a scar left atfer cell division
Explain mitosis with all the phases and cellular events
How is the cell cycle regulated?
Cyclins - dependent kinases (Cdks) (phosphorylates to activate further) - activated by cyclins (by binding)
Explain the mechanism of Cdks and cyclins
Proteins important for M phase are activated by Cdks which are activated by enough cyclin
Explain how different cyclins are expressed at different cell cycle phases - read the graph
Cyclin A: important for G2 phase
Cyclin B: important for transition from G1 to M phase
Cyclin D: important for S and G2 phase - degraded in mitosis
Cyclin E: In S phase - transfer between G1 and G2 phase
Cell cycle is carefully regulated - if not - uncontrolled cell growth - cancer
Exlpain binary fission in bacteria
How do bacteria find the centre of the cell to divide?
Certain proteins shuffle in the cell from one end to other - in total most present in the centre - divide in the centre
