Mitosis and cytokinesis Flashcards
Motors involved in mitosis and predictions for Mutants
a. Kinesin 5 (plus-end-directed motor) : crosslinks and slides overlap microtubules outward, separating spindles or collapsed mitotic spindles.
Mutation effect: spindle poles may fail to separate properly, resulting in monopolar or collapsed mitotic spindles.
b. Dynein (Minus-end-directed motor): Anchors astral microtubules to the cell cortex, pulling spindle poles toward opposite sides during anaphase.
Mutation effect: Spindle orientation would be disrupted, potentially causing misaligned chromosomes and improper cell division.
c. Kinesin-13: Depolymerizes microtubule ends at kinetochores, aiding in chromosome movement during anaphase.
Mutation effect: chromosomes may fail to separate efficiently, leading to anaphase arrest or lagging chromosomes.
d. Kinesin-14 (Minus-end-directed motor): contributes to spindle stability and focuses spindle poles by counteracting outward forces.
Mutation effect: spindle poles may become disorganized or fail to focus, causing mitotic defects.
Mitosis in animal cells vs Plant cells
Animal cell: Mitosis involves significant rearrangements of the cytoskeleton, including microtubules. The centrosomes duplicate, and microtubule asters radiate from them. Breakdown of the nuclear envelope during prometaphase allows spindle microtubules to connect to kinetochores.
Different types of microtubules:
Kinetochore microtubules attach to chromosomes.
Interpolar (overlap) microtubules interact to help spindle pole separation.
Astral microtubules contact the plasma membrane.
Plant cell: Similar processes occur in plants, though they lack centrosomes, and spindle organization differs slightly.
Cytokinesis in Animal cells vs Plant cells
Animal cell: Actin and myosin II form a contractile ring at the cleavage furrow (positioning dependent on signals from spindles, mid zone, and astral microtubules). The cleavage furrow transitions into a dense midbody with overlapping microtubules.
Plant cell: Plants use a structure called the phragmoplast instead of a cleavage furrow. Microtubules align parallel to form the phragmoplast, and new plasma membranes and cell walls develop outward from the center.
