L19- Mechanisms of cell division 1 Flashcards
What happens in each of these stages?
- Prophase
- Pro-metaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
- chromosomes condense
- attach to spindle
- chromosomes align in middle
- chromosomes separate away
- seperate DNA
- Divide cytoplasms and cells
From S phase onwards what are the sister chromatids held together by?
Cohesin rings
What does the centrosome duplicate and what does this?
The s phase by the S-cdk that controls DNA replication.
What does the centrosome do in the cell cycle?
Duplicates, seperates and nucleates MTs wihch form the mitotic spindle.
What activates condensins in prophase?
Phosphorylation by M-Cdk
then DNA stays condensed until after cytokinesis
What happens in prophase?
Chromosomes condense. Centrosomes separate and nucleate more MTs. The mitotic spindle starts to form.
What does the spindle contain?
3 different groups of microtubules
What happens to the number of microtubules, nucleated by the centrosomes from prophase?
The number increases. Microtubules are more dynamic. Change from grow to shrink more often.
What is a catastrophe?
The MTs switch from growing to shrinking
Why do more catastrophes happen after prophase?
Some MAPs (which stabilise MTs) are inactivated when phosphorylated by the mitotic kinase M-Cdk. Proteins that trigger MT catastrophes are activated in mitosis.
Does phosphorylation activate or inactivate the following and what is the consequence?
a. Cdc25
b. condensin
c. nuclear lamins
d. MAPs
a. Activates cdc25 - activates more cdKs
b. activates condensin- chromosomes condense (prophase)
c. Inactivates and activates nuclear lamina?- disassembles
d. Inactivates MAPs- MTs become more dynamic
What establishes anti-parallel interactions between microtubules?
Kinesins
What do anti-parallel interactions between microtubules do?
Stabilise the MTs
Which kinesin can push poles apart by using the anti-parallel interactions between MTs?
Eg5 (a tetramer)
What does Eg5 do?
- Links anti-parallel MTs
- Stabilises the MTs
- pushes spindle poles apart
What inhibits Eg5?
A drug- Monastrol
IN which phase does the nuclear envelope disassemble?
Pro-metaphase
What drives nuclear envelope disassembly?
MCdk. Phosphorylates the nuclear lamins. Has to dephosphorylate for reassembly to occur.
What happens in the prophase to pro-metaphase transition?
Nuclear envelope disassembles, allowing MTs to interact with chromosomes.
Golgi disassembles
Secretion and endocytosis stop
What is the kinetochore?
Specialised protein structure that assembles on to the centrome region of the chromosome in prophase. Where microtubules become embedded.
What happens when kinetochores interact with growing and shrinking microtubules?
They capture the MTs and start moving using kinesins to move one kinetochore to the MT+ end and dynein to move the other towards the MT- end.
Which direction can kinetochores move in pro-metaphase?
In both directions along MTs using dynein and kinesins
WHat must the kinetochores have before mitosis can proceed?
Properly attached from both poles and be under tension. TENSION V IMPORTANT
Are MTs allowed to grow and shrink when bound to kinetochores.
Yes.
