cell division - mitosis Flashcards
what do centromeres operate as
microtubule organising centres
what does the mtoc produce and organise
3 classes of microtubule spindle fibres:
1. astral microtubules
2. polar microtubules
3. kinetochore microtubules
functiom of astral microtubules
anchor the mtoc to the cell membrane
function of polar microtubules
p mt from opposite poles overlap and allow seperation
function of kinetochore microtubules
attach to chromosomes
centrosome division steps
- centrioles sepereate towards the end of G1
- S phase - they duplicate and mature
- M phase - centrosomes move to opposite poles
prophase
- chromosomes condense to become thick and visible
- nuclear envelope breaks down
by the end of prophase - chromosomes are free in the cytoplasm - centrosomes seperate and spindle fibres form - caused by overlapping plus ends of polar microtubules
what is chromsome condensation
when chromatin is disentangled
what does the resolution of sister chromatids enable
accurate chromosome segregation
whats decatenation
seperation of the physical linkage between sister chromatids
prevents dna breakage in mitosis
what is decatenation facillitated by
condensins - which uses atp to remove cohesins
prometaphase
- nuclear envelope are in complete fragments
stimulated by phosphorylation of nuclear pore complexes - each chromatid has a kinetochore
- kinetochore microtubules search for chromosomes
dynamic instability increases - plus ends of polar microtubules overlap
what are kinetochores
complex proteins with a microtubules binding site near the surface
how many kinetchores do each chromatid have
1
whah happens when a kinetechore microtubules binds
chromosome is moved polewards
both kinetochores are bound simultaneously
chromosomes are pulled in both directions
jiggle into position on the metaphase plate
fucntion of mad 2
phosphorylates and inhibits apc
preventing the removal of cohesion rings
metaphase
- centrosomes at opposite poles release microtubules that connect to kinetochores
tension aligns chromosomes at metaphase plate - astral microtubules attach to cell membrane
- polar microtubules are fully overlapping
fucntion of seperase
cleaves cohesins at the centromere
chromatids are now called chromosomes
what does depolymerisation cause and where does it occur
- Depolymerisation at both plus and minus ends of kinetochore microtubules moves chromosomes polewards
anapahse
- seperase
- depolymerisation
- polar microtubules lengthen causing cells to expand
extent of overlap is less in anaphase than metaphase - end of anaphse - poles contain an identical set of chromosomes
anaphase a
seperation of chromosomes
Driven by depolymerisation of microtubules at the plus end
anaphase b
seperation of spindles
Partly driven by depolymerisation of microtubules at the minus end
Partly driven by activity of motor proteins at plus end
MOVING CHROMOSOMES
- Motor proteins ‘walk’ chromosomes along microtubules from plus end
The microtubule depolymerises once the protein has moved past - Motor proteins at the MTOC ‘reel in’ microtubules from minus end
The microtubule depolymerises once past the MTOC
WATCH VIDEO ON PPT
VERY GOOD
TELOPHASE
- complete depolymerisation of the spindle - tubulin enters cytoskeleton
- nuclear envelope reforms from fragmenst left after propahse and prometaphase
- nuclear pore complexes pump in nuclear protein and the nucleus expands
- chromosomes becomes less condensed and enters interphase state
when does mitotic cytokinesis occur
starts in anaphase and finishes immediatley after telophase
mitotic cytokinesis
A contractile ring forms at the old metaphase plate and creates a cleavage furrow
Contraction causes the cytoplasm to divide as the furrow deepens
Cytokinesis mostly follows M-phase
Some mammalian hepatocytes and cardiac cells remain multinucleate
whats the contractile ring made f
two filaments -
actin
myosin 2
where does the contractile ring assemble
between plasma membrane in anaphase
what happens to the cell surface area during mitotic cytokinesis
The contractile force can bend a glass needle
Cell surface area is increased as the membrane incorporates vesicles during cleavage
what si the plane of division determined by
signals generated by the spindle during anaphase
Exact mechanism is unknown but moving the spindle leads to incorrect division
what does mitosis and cytokinesis ensure
Mitosis ensures inheritance of a full set of chromosomes
Cytokinesis ensures inheritance of a full set of organelles
