BIOL10004 Chapter Notes - Chapter 8: Cell Membrane, Cell Plate, Actomyosin Ring
29 Jun 2018
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Mitosis in animal cells
• Prophase:
o Chromosomes become recognizable because it condensed due to chromatin
o Becomes visible chromosomes within nucleus
o DNA coiled around nucleosomes (histone proteins)
o Each condensed chromosome consists of two identical sister chromatids
o Held together at constricted region called centromere
o Late prophase, RNA synthesis ceases and prominent nucleoli shrink and disappear
o The mitotic spindle
• Microtubules in animal cell emanate from structure termed centrosome
• Centrosomes produce increasing numbers of fibers
• Arrays of radial fibers are called asters
• Asters grow, centrosomes move apart
• Due to interactions between fibers that meet midway between the centrosomes
• Asters are dynamic
• Grows and shrinks rapidly
• Dynamic instability
• Spindle fibers constantly probe among chromosomes, ensuring that all
chromosomes will eventually contact some microtubules of aster
• Prometaphase:
o Asters form cage-like array of microtubules over surface of nuclear envelope
o Nuclear envelope then disassembles in a few seconds
o Microtubules push into nuclear region
o Chromatin provides stimulus for growth of microtubules towards nuclear region
o Microtubules form biconical structure
o Spindles grow towards chromatin, bind to special structures on chromosomes,
kinetochores
o Kinetochore fibers are special microtubules
o Stabilized by insertion into kinetochore
Document Summary
Initial movement of chromosomes to opposite poles: anaphase b: Initial furrowing is rapid but completion of telophase and final separation during cytokinesis is slow: two separate cytoskeletal systems needed. Spindle during prophase and contractile ring during anaphase-telophase: overlapping fibres that run between poles become aggregated during constriction into tight rod called midbody, quite stable, often continues to hold daughter cells together before it is cleaved. Mitosis and cytokinesis in plant cells: mitosis in plants remotely same as animals cells, displays two major structural differences, plant cells do not have centrosomes. Forms cell plate: before prophase, microtubules form band close to cell wall preprophase band, band predicts exactly where phragmoplast will join growing cell plate to older walls. Checkpoint control of the cell cycle: critical for cell to proceed through cell division, only when accurate distribution of genetic material is done that it can continue.
