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Cell Cycle and Mitosis

Cell Cycle and Mitosis. Cell Cycle. Only a Eukaryotic Process Unicellular: asexual reproduction Multicellular : growth and repair Rate may differ depending upon: Type of cell Age of cell External factors that affect cells. Type of Cell.

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Cell Cycle and Mitosis

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  1. Cell Cycle and Mitosis

  2. Cell Cycle • Only a Eukaryotic Process • Unicellular: asexual reproduction • Multicellular: growth and repair • Rate may differ depending upon: • Type of cell • Age of cell • External factors that affect cells

  3. Type of Cell • The function of the cell, type of tissue often determine the rate of it’s cell cycle • Fastest include: intestinal, skin, bone marrow, hair • Slowest: bone, liver, kidney

  4. Age of Cell/Organism • In multicelled organisms the rate of the cell cycle also depends upon the age of the cells • “Age” is a factor of cell division and cell death • Young: cell division > cell death = growth • Middle: cell division = cell death • Old: cell division< cell death

  5. Why can’t organisms live forever? Cells cannot grow and divide indefinitely. At the end of chromosomes are small ‘caps’ called telomeres that help keep the DNA from uncoiling. Every time the DNA is replicated a piece of the telemere is lost. When the telomere is gone the DNA can no longer replicate and the cell dies. Interestingly, telomeres are found in the cells of multicelled organisms, but, not unicellular…what would happen if there were?

  6. External Factors • Factors outside of the cell or organism can affect the cell cycle. • Cells are exposed to many environmental factors that can directly influence the control and regulation of the cell cycle • Examples include: Drugs, Alcohol, Smoke, Radiation, Toxins, Viruses • All of these substances disrupt the cell cycle and can cause cells to divide uncontrollably forming the tumors associated with many cancersand so are referred to as carcinogens

  7. Genetic Factors • Some mutations to genes can result in changes to the cell cycle. • The BRCA1 gene can cause breast cancer • Progeria is a genetic disorder marked by rapid aging

  8. The Cell Cycle • Occurs in 3 phases • Interphase: preparation for division • Mitosis: nuclear division • Cytokinesis: cell division

  9. INTERPHASE • Use to be referred to as the cell’s ‘resting phase’, however, actually a lot of activity is occurring during this time. • Approximately 80% of cell’ life is spent in interphase • Marked by 3 distinct stages: • Gap 1 (G1 ) follows cytokinesis, time of cell growth, replication of organelles (1st Checkpoint) • Synthesis(S) Replication of DNA in preparation for division • Gap 2: (G2 )growth slows, cell enzymes check DNA (2nd Checkpoint)

  10. MITOSIS • M Phase: Process that divides the nucleus with replicated DNA • Approximately 15% of cell’s life cycle • 4 Stages • PROPHASE: “before”; replicated DNA uncoils • METAPHASE: “after”; chromosomes align (3rd Checkpoint) • ANAPHASE: “opposite”; chromosomes separate • TELOPHASE: “across”; chromosomes recoil

  11. G0 • Resting phase where certain cells leave the cell cycle and stop dividing • Some cells, once formed, remain in G0 for the life of the organism. These cells cannot be replaced once damaged. Examples: Nerve and Muscle • Some cells enter an extended period of G0 , however, can be replaced overtime. Examples: Liver and Kidney

  12. CYTOKINESIS • Division of the cell • Means “to move the cell” • Approximately 5% of cell’s life • Process differs in Heterotrophs(Animals) Autotrophs(Plants) due to presence of cell wall

  13. Cell Cycle Checkpoint 3 Are chromosomes aligned? cytokinesis NECK TIE Checkpoint 2: Has DNA replicated correctly Checkpoint 1: Is cell getting to large ?

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