Lecture 9 Flashcards
Mitosis describs the process of ________ and cytokinesis describes the process of __________
Replicating and segregating the sets of chromosomes, cytokinesis is making the 1 cell into 2
Eukaryotic cell cycle 4 phases
-Growth phase (G1)
-Synthesis phase (S)
-Growth phase (G2)
-Mitotic (M)
In cytokinesis, where are actin and myosin highly concentrated
Contractile ring
What does the contractile ring do
Helps 2 cells pinch apart
Cytokinesis is the final step in cell division in which the _________ of a single eukaryotic cell is divided to form two daughter cells
Cytoplasm
First visible change in cytokinesis is the appearance of a
Cleavage furrow
What structure is responsibe for the contractile ring
Cleavage furrow
Contractile ring assembles beneath
Plasma membrane
Contractile ring pulls membrane _______
Inward
True or false: membrane vesicles fuse to PMAssembly of contractile ring
- Actin, tubulin and myosin disassemble in mother cell
- Monomeric actin and myosin accumulate at site of contractile ring (ANAPHASE)
- Local actin polymerizes- mediated in part by formin- establishing site of nucleation by unbranched actin
What happens as cleavage furrow deepens
Vesicles fuse to PM, surface area expansion
Adding taxol during cytokinesis
Prevents depolymerization of MTs, cant break apart asters, cell dies
Microtubules must _______ to facilitate formation of contractile ring
Depolymerize
The midbody contains
The central spindle, consisting of densly packed microtubules of the spindle midzone (actin-tubulin)
Disassembly of contractile ring
- During contraction, actin filaments depolymerize and exit ring to maintain size and volume
2.Contractile ring is completely disassembled with formation of Midbody - Midbody tethers daughter cells together (right before they seperate)
Local activation of RhoA triggers
Assembly and contraction of contractile ring
Some things RhoA does:
-regulates remodelling of actin skeleton
-promotes actin polymerization
-binds and activates formin to promote actin nucleation at contractile ring
-Activates Rho Kinases (such as ROCK1)
Rho in muscle contraction
Rho –> mDia (formin) –> profilin –> actin polymerization
What ensures equal distribution of chromosomes
Spindles signal for furrow formation midway between 2 poles (anaphase)
ER during cytokinesis
Segregates during interphase, also necessary for orientation of contractile ring
Mitochondria during cytokinesis
Multiply prior to segregation, localize to cleavage furrow - likely to supply energy
Golgi during cytokinesis
Fragments during M-phase in mammals, form cell plate in plants
Asymmetrical division
Positioning of cleavage furrow 3 mechanisms
- Astral stimulation model
- Central spindle model
- Astral relaxation model
Astral stimulation
Signals being moved down the MTs toward the middle of the PM where furrow forms
Central spindle stim model
Spindle mid zone (overlap) sends signals that transmit to cell cortex to activate Rho signalling pathway - formation of contractile ring
Astral relaxation model
Relaxation of any contractile force where MTs meet PM - contractile force exerted only at cleavage furrow site