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 cancers and 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 (G 1 ) follows cytokinesis, time of cell growth, replication of organelles (1 st Checkpoint) Synthesis(S) Replication of DNA in preparation for division Gap 2: (G 2 )growth slows, cell enzymes check DNA (2 nd 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 (3 rd Checkpoint) ANAPHASE: “opposite”; chromosomes separate TELOPHASE: “across”; chromosomes recoil

11. G0G0 Resting phase where certain cells leave the cell cycle and stop dividing Some cells, once formed, remain in G 0 for the life of the organism. These cells cannot be replaced once damaged. Examples: Nerve and Muscle Some cells enter an extended period of G 0, 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 HETEROTROPHSAUTOTROPHS Cell membrane indents at cleavage furrow and cell is ‘pinched’ in half The cell divides from the center with the formation of cell plate(cellulose) and cell is ‘cut’ in half

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