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Transcript of Mitosis
Cell cycle control
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
Events of prophase reverse
Spindle fibers disappear
Nuclear membrane reforms
Ring of protein fibers pinches cell into two
Daughter cells separate
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"
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
This picture is called a karyotype
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)
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