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BIO 201 (90)
Lecture 29

BIO 201 Lecture 29: Cytokinesis and Apoptosis
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Department
Biological Sciences
Course Code
BIO 201
Professor
Lara Hutson

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BIO 201 Dr. Lara Hutson Lecture 29 Notes 4/19/17 Cytokinesis: When cell actually divides. Not technically part of mitosis but is part of M phase! Cytokinesis in Animal Cells ● After chromatids (now daughter chromosomes) separate and spindle breaks down, a contractile ring forms ● Contractile ring tightens → divides parent cell into two daughter cells ● No gaping hole since lipids like each other → fill up hole What Do Animal Cells Use for Cytokinesis? ● Experiment: Treat cells at the end of anaphase with drugs 1. Depolymerize actin using Cytochalasin D (fungus toxin) a. Result: No cytokinesis! 2. Inhibit myosin ATPase activity using Blebbistatin a. Result: No cytokinesis ● Conclusion: Actin and myosin are both required for cytokinesis! Actin, Myosin, and the Contractile Ring ● Actin and myosin mediate contraction of contractile ring → cytokinesis ● At beginning of cytokinesis, actin filaments run parallel around contractile ring in a random orientation ● Double headed myosin anchored together at their tails find actin filaments oppositely oriented ○ Get actin filaments to overlap more ○ Myosin is (+) end directed actin motor → pull filament in opposite direction → increase degree of overlap ● Initial trigger for assembly of actin-myosin complex is unknown Cytokinesis in Plants ● Plant cell wall made of cellulose (secreted) ● No contractile ring ● After chromatids separate and spindle breaks down, vesicles are transported to the plane of cell division ● Secretory vesicles fuse with each other, separating daughter cell cytoplasms ○ Vesicles made of lipids (amphipathic; don’t like water) → fusion ○ Spontaneously assemble into two new membranes and also fuse into plasma membrane ● Vesicles carry polysaccharides (cellulose) for new cell wall The Cell Plate ● Microtubules ○ Anterograde transport - transport of vesicles along MTs to plasma membrane ■ MTs have (+) ends at plasma membrane ■ Vesicles transported by kinesin (+-end directed) ○ During mitosis, MTs have (+) ends at cell plate ■ Vesicles transported along MTs towards cell plate ((+) end) and fuse together → form new plasma membrane ■ Vesicles contain cellulose → help form new cell wall Two Types of Cell Death ● Necrosis (“death”): cell death due to acute damage
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