Bio 201 1st Edition Lecture 28Outline of Last Lecture I. MitosisA. Steps of MitosisB. Spindle StructureC. Spindle FunctionOutline of Current LectureI. Spindle Assembly CheckpointA. Role of TensionII. CytokinesisA. In AnimalsB. In PlantsCurrent LectureI. Spindle Assembly Checkpoint-This checkpoint is during the metaphase anaphase transition. It ensures that both sides of kinetochore have microtubules attached, before degrading the cohesin. -If anything goes wrong during the metaphase or anaphase, it can be very bad for cells.-Non-disjunction- Abnormal chromosome segregation during mitosis or meiosis. -Karyotype- #/ type of chromosome in a cell.-Aneuploidy- Cells inherit the wrong #/ type of chromosome: generally incompatible with life but often seen in cancer cells. -The kinetochore is central to preventing aneuploidy These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Cohesin holds the sister chromatids together until anaphase, where it then begins to degrade. It only degrades when MTs from both poles are attached and chromosomes are aligned at the metaphase plate. A. Role of Tension- During metaphase, constant depolymerization at the centrosome might pull on the chromosomes-Hypothesis- Tension coming from opposite poles is the signal for cohesion degradation. -Experiment- Use glass needle to pull on last chromosome before 2nd MT attaches. Result: Cohesin degradation Chromosome Segregation-Tension is the signal for cohesion degradation (anaphase) II. Cytokinesis- The separation of daughter cells.A. In Animal Cells-After chromatids have separated, a contractile ring forms, this ring tightens, eventually dicing parent cell into 2 daughter cells. -Eukaryote cells need actin and myosin for cytokinesis. Actin and double-headed myosin are responsible for the formation and tightening of the contractile ring and cytokinesis. B. In Plant Cells-There is no formation of a contractile ring-After chromatids have separated, lipid vesicles invade region between 2 nuclei, this region is called the cell plate. -The vesicles eventually fuse and fuse with the plasma membrane, dividing daughter cells. -Plant cells divide by fusion of vesicles at the cell
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