The Cell Cycle

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The Cell Cycle
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Growth

• Increase the number of cells (for multicellular
  organisms)
• Do not confuse with reproduction
• Growth happens by MITOSIS
• Mitosis is cell division
• (really nuclear division)

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Why must cells divide?(Why cant they just
expand?)

• Surface area to volume ratio
• There is an optimum size for servicing the needs
  of the cell (its nutrients and waste removal)

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Four Phases of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromosomes Condense
• Centrioles spread apart
• Nuclear membrane breaks down

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Metaphase

• Sister chromatids line up in the center of the
  cell
• Spindle fibers form
• Centromere attaches to the spindle fibers and
  becomes a kinetichore

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Anaphase

• Sister chromatids separate
• (The sister chromatids become chromosomes)
• The chromatids separate by the kinetichores
  traveling along the spindle fibers (reeling them
  in as they move)

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Telophase

• Spindle fibers break down
• The Nuclear Membrane reforms

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Cytokinesis

• The cytoplasm pinches off separating the two new
  daughter cells

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The Cell Cycle

• Growth and repair of tissues
• Daughter Cells
• Genetically identical (Same DNA sequence)

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Four Stages of the Cell Cycle

• Mitosis
• G1
• (G0)
• S
• G2

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G1 PhaseGrowth

• Cell Work
• Contract and Expand (Muscles)
• Fight bacteria and viruses (White blood Cells)
• Cover and Protect (skin)
• Secrete enzymes, hormones, and fluids
• Carry nerve impulses
• Carry Oxygen and Carbon dioxide (Hemoglobin)

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G0 Phase

• Cells do not divide but continue their cell work.
  
• Nerve Cells
• Muscle Cells
• Bone Cells

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S PhaseSynthesis

• DNA replication (Making Sister Chromatids)
• A-T
• G-C
• DNA polymerase
• Leading Strands (5-3)
• Lagging Strands
• Replication Fork
• DNA ligase (repair)
• Chance for mutations

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G2 PhasePreparation for Mitosis

• Centrioles Replicate
• Build up of Organelles (ribosomes, golgi
  apparatus, etc.)

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Cell Cycle Control

• External Regulators (Outside Cell)
• External Promoters Hormones
• External Inhibitors Cell to Cell proteins
• Internal Regulators (Inside Cell)
• Internal Promoters Cyclins (proteins) Proto
  Onco Genes
• Internal Inhibitors p53Tumor Supressor Genes

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Restriction Point

• Enough Cyclins (trigger proteins) build up to
  signal the beginning of the next phase of the
  cell cycle

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p53

• A protein inhibitor that stops the cell cycle and
  enables the cell to either repair itself or
  commit cell suicide
• apoptosis

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Cancer

• Problems with the cell cycle regulators
• Cyclins or p53 are not functioning and the cell
  moves to the next phase of the cycle without
  completing proper replication or proper division.
• See cancer information videos
• http//science.education.nih.gov/supplements/nih1/
  cancer/activities/activity2_animations.htm