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Cell Cycle and Mitosis

Cell cycle and mitosis

Patricia Wilkins

on 7 April 2016

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Transcript of Cell Cycle and Mitosis

Why do cells divide?
Cell Cycle Control
Early prophase
Late prophase
Cell Cycle and Mitosis
DNA begins to condense into chromosomes
Nucleolus disappears
Nuclear membrane begins to break down
Centrioles move to opposite poles
Middle prophase- Spindle fibers form
Chromosomes are attached to spindle fibers
Asters formed in animal cell
Spindle fibers position chromosomes along center of cell- equatorial plate
spindle fibers
polar and kinetochore
Spindle fibers shorten
Centromeres divide
Sister chromatids are pulled apart
Chromatids reach the poles
Cytokinesis begins
Events of prophase reverse
DNA decondenses
Spindle fibers disappear
Nuclear membrane reforms
Nucleolus reappears
Asters and centrioles disappear
Ring of protein fibers pinches cell into two
Daughter cells separate
All done!
Back to interphase...
Most of a cells life spent here
Divided into stages
G1: Growth or Gap 1
s: DNA Synthesis
G2: Growth or Gap 2
Cytokinesis in Plant Cells
Characteristics of Interphase Cells
DNA is in a loose state called chromatin
DNA is replicated during S phase
Cell is "doing its job"
Chromosome Structure
Chromsomes are complexes of equal parts DNA and protein
Histones maintain the shape and aid in tight packing
During S phase the DNA replicates to form sister chromatids
Sister chromatids are exact copies of each other
Chromatids are held together at the centromere
Humans have 46 chromosomes, arranged in 23 pairs

Why pairs?
This picture is called a karyotype
Big Questions
Why do cells divide?

How does a cell control when it divides?

What happens when cells divide uncontrolled?
The cell cycle is controlled by checkpoints - cyclins
If a cell does not correctly fufill checkpoint requirements, cell cycle is arrested

Problem can be fixed, or cell can eliminate itself (apoptosis)
G1 Checkpoint
"Cell Growth" Checkpoint
Makes the decision of if the cell will divide. Is cell healthy and large?
Stop growth:
R Point ( restriction point)

depletion of nutrients
changes in temp or pH
DDI - density - dependent inhibition

Nerve and muscle cells remain here
If cell gets past this, will most likely complete rest of cell cycle
Oncogenes tend to speed up the cell cycle.

Activating mutations lead to cancer.
G2 Checkpoint

"DNA Synthesis" Checkpoint''
DNA replication checked ( all chromosomes replicated
p53 gene- normally halts cc
If cell passes, mitosis begins.
Mitosis Checkpoint
Prevents entereing anaphase until all chromosomes are attached to the spindle
Triggers exit from mitosis.
Signals beginning of growth.
Tumor suppresor genes tend to slow down the cell cycle.

Deactivating mutations lead to cancer.
External regulators
Growth factors
wound healing
Differences plant and animal cell cycle
no centrioles
cell plate
no asters
no cell plate
What phase?
Full transcript