Cell Cycle and Cell Division

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Cell Cycle and Cell Division

• Chapter 5
• Belk and Borden
• Biology Science for Life

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Cell Division

• - the process a cell undergoes in order to make
  copies of itself.
• Why do cells divide?

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What is Cancer?

• mitosis gone mad
• - a disease that begins when a single cell
  escapes from the regulation of its own division
• Tumor
• Benign vs Malignant

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The Cell Cycle

• -all the events that occur when a cell divides
• -time required can vary from minutes to days,
  depending on the cell
• Salmonella 29 min
• Red B. C. 120 days

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DNA Chromosomes

• DNA as chromatin strands and chromosomes
• Sister Chromatids
• Centromere
• Why do chromosomes form?

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Interphase (G1, S, G2)(about 90 of the cell
cycle time)

• Cell grows during all 3 subphases by making
  proteins and organelles
• G1 first growth phase

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Interphase (G1, S, G2) (about 90 of the cell
cycle time)

• S phase DNA is copied (synthesis) so each
  daughter cell has a complete set of chromosomes
  at the end of the cell cycle

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Interphase (G1, S, G2) (about 90 of the cell
cycle time)

• G2 phase second growth phase
• All through interphase, the cell is fulfilling
  its function
• At maximum volume to surface ratio, cell either
  remains in interphase or enters mitosis

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Mitosis Prophase

• Chromatin condenses into chromosomes
• Each duplicated chromosome appears as 2 identical
  sister chromatids
• Mitotic spindle begins to form in cytoplasm

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Mitosis Prometaphase

• Nuclear membrane disintegrates
• Spindle fibers interact with chromosomes
• The dance of the chromosomes begins

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Mitosis Metaphase

• Chromosomes are aligned at middle of cell
• Identical chromatids of each chromosome are
  attached to spindle fibers radiating from
  opposite poles of the cell

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Mitosis Anaphase

• Paired centromeres of each chromosome separate,
  freeing sister chromatids from eachother
• Each chromatid now a chromosome
• Sister chromatids are pulled to opposite poles of
  the cell

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Mitosis Telophase

• 2 new nuclei form at two poles of the cell where
  chromosomes have gathered
• Chromosomes uncoil and revert to chromatin form
• Mitosis (division of one nucleus into two
  identical nuclei) is complete

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Cytokinesis
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Allium root tip (onion) a mitosis classic!
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Classify Cells relative to Cell Cycle Phase link
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Control of the Cell Cycle

• Cells require nutrients and growth factors to
  divide (example PDGF fibroblasts)
• Density dependent inhibition also regulates cell
  division
• Adhesion of cells is also involved. Cells
  normally stop dividing if they lose their
  anchorage.
• The role of regulatory proteins at the G1
  restriction point is also critical.

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Control of the Cell Cycle

• Regulatory proteins pace and control cell cycle
  events at checkpoints
• G1 checkpointmonitors nutritional status, growth
  factors, cell density restriction point
• G2 checkpointmonitors DNA replication and cell
  size
• Metaphase checkpointmonitors chromosome
  attachment to spindle fibers

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Mutations

• Changes (errors) in the genes that code for cell
  cycle regulatory proteins and tumor suppressor
  proteins are involved in cancer
• Proto-oncogenes code for growth factors
• Mutated proto-oncogenes (oncogenes) can
  overstimulate cell division and override the G1
  checkpoint
• Mutated tumor supressor genes fail to produce the
  proteins that prevent tumors

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Healthful Decisions to reduce Cancer Risk

• Avoid carcinogenic addictions!
• Eat whole foods (fresh fruit and grains)
• Exercise regularly to boost immune system
• Dont drink alcohol in excess
• Dont get sunburned
• Undergo regular screening and self-examination