Download The Cell Cycle

The Cell Cycle
MITOSIS
Outcomes
Explain the events of the cell cycle
1.
Interphase
Mitosis
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Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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.
2.
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
● 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
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
Interphase
● Majority of time spent in interphase
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- 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
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
I / PMAT
- Telophase
● Cytokinesis: occurs after Telophase
- division of cytoplasm
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
Early Prophase
Late Prophase
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
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)
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
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
Whitefish Prophase
Whitefish Metaphase
Whitefish Anaphase
Whitefish Telophase
REVIEW
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)