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Mitosis
Somatic Cell Division
Purpose
• Reproduce asexual unicellular organisms
• Bacteria
• Archaeans
• Protists
• Replicate non-sexual/ somatic cells in multicellular organisms
• Replace dead/ dying cells in tissues
• Growth
• Development
When?
When not?
• If cells enter G0 phase
• Full maturity (nerve cells)
• Cells need to ‘rest’
• If cells do not pass the G1 checkpoint due to
• Insufficient growth/ maturity
• Inadequate resources in cell’s environment
• If cells do not pass the G2 checkpoint due to
• Improper replication of cell’s DNA during S phase
• Insufficient growth of cell or amassment of cell parts
• Lack of critical proteins, enzymes, or other signaling molecules
Stages of Mitosis
• Prophase
• Chromosomes condense; nuclear envelope & nucleolus degrades;
centrosomes migrate; spindle forms (kinetochore fibers vs. polar fibers)
• Metaphase
• Chromosomes migrate to middle of cell
• Anaphase
• Chromatids separate, moving toward opposite poles
• Telophase
• Chromosomes at opposite poles; nucleolus & nuclear envelope reassemble;
spindle fibers disassemble; chromosomes  chromatin