Lecture 23 Cell Cycle II Flashcards
What is condensin?
Five subunit protein complexRelated to cohesinContains 2 SMC subunits and 3 non-SMC subunitsForms ring-like structure and uses ATP to promote compaction and resolution of sister chromatids
What triggers assembly of mitotic spindle?
M-Cdk
What are kinetochore microtubules?
Attach each chromosome to spindle pole Plus end of each microtubule is attached to sister chromatid pairs at large protein structures called kinetochores
What are interpolar microtubules?
Hold two halves of spindle together Plus ends from one pole interact with plus ends from other poles Gamma-turc binds to negative end to nucleate and elongate microtubules
What are astral microtubules?
Interact with cell cortex Radiate outward from the poles and contact the cell cortex helping to position the spindle in the cell
Describe centrioles
Protein organelles called centrosomes consists of pericentriolar matrix and a pair of centriolesContains gamma-turc > 50 copies
Kinesin 5:
two motor domains that interact with plus end of antiparallel microtubule Move the 2 anti-parallel microtubules past each other to force or push the spindle poles apartWalks towards plus end-forces centrosomes apart
Kinesin 14:
minus oriented directed motor with a single motor domain Walks towards minus end and pulls poles together
How does Kinesin 5 and 14 work together?
5 is pushing poles apart while 14 is pulling the poles together. Why?rope is stretched apart by the push-pull phenomenon. maintain integrity of spindle
Kinesin -4,10
Also called chromokinesins Plus directed motorsTowards plus endPush attached chromosomes away from the pole
What is the push-pull concept on chromosomes?
Kinetochore microtubule attached to kinetochore causing the chromosome to be pulled towards pole but kinesin 4,10 is pushing chromosome away from pole
What are dyneins?
Minus end direct motorsLink plus ends of astral microtubules to actin skeleton at cell cortexBy moving towards minus end of microtubule, the dynein motors pull the spindle poles away from each other
What is the outer collar of a kinetochore?
It is the part of the kinetochore that multiple microtubules are attached to There is an exposed open end for addition and removal of tubulin subunits*at first, kinetochore binds laterally to a microtubule and it then slides along chromosome.. Lateral attachment converted to end-on attachment
Bi-orientation:
Sister chromatids must attach to opposite poles of mitotic spindle. There for a bipolar attachment is formed from attaching kinetochore to microtubules on opposite side of chromosomeThis is called bi-orientation
Depolymerization:
Chromosome movement happens because of 3 forces, one of them being depolymerization.It is a major force that pulls the kinetochore and chromosome towards the spindle pole. By depolymerizing the plus end of the microtubule, it drives the pulling of the kinetochore poleward Pulls collar which is connected to chromosome
Microtubule flux:
Chromosome movement is done by 3 forces, microtubule flux is one of them.Microtubules move toward spindle poles while being dismantled at minus ends Tubulin added to plus end while being removed at minus end-interpolar microtubules causing treadmill or escalator
What is polar ejection force?
third force that moves chromosomesKinesin-4,10 motors on chromosomes interact with microtubules and transport chromosomes from poles Results in push-pull phenomenon
What activates APC/C?
M-Cdk activates APC/C and allows Cdc20 to attached to APC/C to become fully activated
What is the difference between Anaphase A and B?
A: chromosomes move apart due to spindle microtubule depolymerization at kinetochoreB: Separation of spindle poles themselves by kinesin-5 motor proteins; also dynein pulls pole apart
What is the first visible change in cell during cytokinesis?
Cleavage furrowUnderlying the cleavage furrow is the contractile ringComposed of actin and myosin filaments Rings contract, vesicles fuse with membrane to create new membrane
The assembly of ring also results from local formation of new actin filaments which depends on what?
formin : remember, formin is a protein that nucleates assembly of linear, unbranched actin filaments
How do mitogens cause cell-cycle entry into S-phase?
mitogens bind to receptorRas causes activation of MAP kinase cascade Leads to increase of gene reg proteins including MycMyc increases expression of G1 cyclinsG1 cyclins activate CdkG1-Cdk activates group of gene reg factors called E2F proteinsE2F binds to promoters of G1/S cycling and S cyclin and DNA synthesis protein genesThen enters into S phase of cell cycle
How is E2F protein inhibited?
Rb protein interaction-shuts down entry into S phase
What causes E2F to be activated?
Active G1-Cdk phosphorylates Rb to inactivate the Rb protein (reduces binding to E2F)
