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Honors Biology mitosis and cell cycle. Image credits: Biology Life on Earth 8th ed

Christopher Himmelheber

on 21 January 2014

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Transcript of Mitosis

Why do cells divide?
Cell cycle control
Early prophase
Late prophase
Cell Cycle and Mitosis
DNA begins to condense into chromosomes
Nuclear membrane begins to break down
Centrosomes move to opposite poles
Spindle fibers form
DNA is fully condensed
Nuclear membrane is gone
Chromosomes are attached to spindle fibers
Spindle fibers position chromosomes along center of cell
Spindle fibers shorten
Sister chromatids are pulled apart
Chromatids reach the poles
Cytokinesis begins
Events of prophase reverse
DNA decondenses
Spindle fibers disappear
Nuclear membrane reforms
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
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

If a cell does not correctly fufill checkpoint rquirements, cell cycle is arrested

Problem can be fixed, or cell can eliminate itself (apoptosis)
R Point
Major checkpoint

If cell gets past this, will most likely complete rest of cell cycle
Checkpoints are controlled by the activity of cdk proteins

Cyclin Dependent Kinases

cdks are always present in the cell

Cyclins cycle during cell cycle
Active cdk-Cyclin complexes phosphorylate key control elements

pRb is a major control protein in cell
Oncogenes tend to speed up the cell cycle

Activating mutations lead to cancer
Tumor supressor genes tend to slow down the cell cycle

Deactivating mutations lead to cancer
Full transcript