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MITOSIS
The Cell Cycle
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Outcomes1. Explain the events of the cell cycle ● Interphase ● Mitosis ● Prophase ● Metaphase ● Anaphase ● Telophase
● Cytokinesis 2. Use a simulation to demonstrate the behaviour of
chromosomes during mitosis 3. Observe and identify stages of the cell cycle from
onion root tip cells, and determine the duration of each stage.
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Cell Cycle● Recall: cell divisions after
fertilization - continues to increase in size, maintains grown individual
● Division of body cells (somatic cells)
● Cell cycle: phases, no pauses in between
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● There is a maximum cell size ! because of surface area:volume (impact on diffusion)
● Is the reason why large organisms are made of many tiny cells
● Cells divide in order to create more cells, either to increase organism’s size or replace old/damaged cells
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Cell Cycle Phases
● Division Phase: components of cytoplasm and nucleus of parent cell divided - gives rise to TWO identical daughter cells - Mitosis: duplication of chromosomes, each daughter cell has same number of chromosomes as parent cell - Cytokinesis: divides cytoplasm and organelles equally
● Interphase: stage between divisions - G1: rapid growth - S: synthesis of chromosomes (duplication)- G2: growth, preparation for division
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Interphase● Majority of time spent in interphase
- includes G1, S, G2 ● Cells not actively dividing
- grow and undergo metabolic processes ● Chromosomes uncondensed (chromatin) ● G1: period of rapid growth,
chromosomes unduplicated ● S phase: prepare for division, duplication
of chromosomes ● G2: growth, completes prep for division
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Stages of Mitosis● Recall: mitosis is the process in which a parent cell
divides into two identical daughter cells with the same number of chromosomes as the parent.
● 4 stages of Mitosis - Prophase- Metaphase- Anaphase- Telophase
● Cytokinesis: occurs after Telophase- division of cytoplasm
I / P M A T
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Prophase● Early Prophase: chromosomes start to
condense- become shorter, thicker and visible
● Centrioles move to opposite poles - site of attachment of protein-based SPINDLE FIBRES- “guide wires” for attachment and movement of chromosomes - form spindle apparatus - most plant cells lacking centrioles
● Centromere: joins the two chromatids, anchors chromosomes to spindle fibres
● Late Prophase: nuclear membrane dissolves
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Early Prophase Late Prophase
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Metaphase● Chromosomes composed of
sister chromatids move toward centre of cell- line up on equatorial plate “like train tracks”
● Attached to spindle fibres at centromere
● Most visible at this stage- dark, thick filamentous structures
● Nuclear membrane completely dissolved
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Anaphase● Centromeres divide ● Sister chromatids move to
opposite poles - now considered chromosomes (unduplicated)
● Same number and type of chromosomes at each pole (if mitosis occurs correctly)
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Telophase● Last phase of mitosis ● Chromosomes reach
opposite poles, begin to lengthen (forming chromatin)
● Spindle fibres dissolve ● Nuclear membrane begins
to form around each mass of chromatin
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Cytokinesis● Chromosomes already at each
pole, nuclear membrane forming
● Cytoplasm begins to divide ● Animal cells: furrow develops,
pinches off the cell into two parts (TWO daughter cells) - marks end of cell division
● Plant cells: cell plate forms between two chromatin masses - develops into new cell wall
Mitosis and Cytokinesis cell division on contrast microscope
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Whitefish Prophase
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Whitefish Metaphase
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Whitefish Anaphase
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Whitefish Telophase
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REVIEW
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Cell Biological Clock
● Cells have a finite number of divisions they can undergo ● Internal memory for number of divisions already undergone
ex) heart cells: frozen after 10 divisions, underwent another 40 when thawed- always total of 50 divisions no matter how long frozen
● Not all cells have same ability to mitotically divide ● WHY???
- AGE: stop dividing (due to length of telomeres)- SPECIALIZATION: more specialized, reproduce less
● 2 types of cells divide endlessly - spermatagonia- cancerous cells (spend most of life cycle in cell division not interphase)