Biology 1001A Lecture Notes - Lecture 2: Spindle Apparatus, Sister Chromatids, Chromosome Segregation
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Test 1 - Cycle 2 - Cell Cycle
Mitosis
Prophase
- chromatin condenses
- nucleolus disappears… RNA synthesis stops
- mitotic spindle begins to form between the 2
centrosomes as they migrate to opposite
sides of the cell
- spindles develop microtubules that radiate
from spindle poles
Prometaphase
- nuclear envelope breaks down
- spindle microtubules grow from centrosomes
- kinetochore (complex protein) forms on each
centromere
- kinetochore microtubules bind to the
kinetochore which pulls the chromatids to
opposite sides
Metaphase
- spindle microtubules move the
chromosomes to the metaphase plate
(middle)
- chromosomes are fully condensed
Anaphase
- sister chromatids separate, being pulled at
the kinetochore & move to opposite spindle
poles
Telophase
- spindles disassemble & chromosomes
decondense
- nucleolus reappears
Non-Nuclear Genomes - genetic material not found in the nucleus
Plants: circular DNA found in the chloroplasts & mitochondria
Animals: circular DNA found in the mitochondria
Mitotic Spindle
- made up of microtubules and their proteins
- Chromosome segregation: equal distribution of daughter chromosomes in each of the two
cells that result from cell divison
- kinetochore microtubules: connect the chromosomes to the spindle poles, chromosomes
walk themselves to along the microtubules using motor proteins
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- nonkinetochore microtubules: extend between the spindle poles without connecting to
chromosomes at the spindle midpoint, the microtubules from one pole overlap with the
microtubules from the opposite pole to cover the entire cell
Checkpoints
1. G1/S - check for damage to the DNA
2. G2/M - check to ensure DNA is fully replicated
3. Mitotic Spindle (Metaphase) - ensures chromosomes are attached to mitotic spindle so that
they align correctly at the mitotic plate
Apoptosis - programmed cell death, when the cell is no longer needed (surplus)… it no longer
divides
- cells gauge their age with the length of their telomeres (shorter = older)
- if cell is damaged, white blood cells engulf invaders
Location of Actively Cycling Cells
- reproductive cells (gametes), stem cells (bone marrow), epidermis (other tissues that need to
be repaired constantly), meristematic tissue (roots, shoots & trunks of plants)
- ** most cells most of the time are not cycling** (in G0 phase)
Linear Chromosomes: found in almost all eukarya
Circular Chromosomes: archea, bacteria (mitochondria, chloroplasts)
Composition of Microtubules, Intermediate filaments, & Microfilaments
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