The Cell Cycle


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  • Erythrocytes have no nucleus, are made in the red marrow of bones, and live about 120 days. As red blood cells wear out in the bloodstream, they are taken in by the spleen, an organ on the left side of the abdomen below the stomach, and destroyed. Parts of the old cells are salvaged to make new red blood cells. Skin cells are dividing every day (about once every 20 hours). Embryonic human cells divide about once a day (in the early stages of development). Some nerve cells never divide after being formed in an embryo, which means they live as long as you do!
  • Who has heard of Mitosis – Meiosis?
  • Toddler/childhood phase of rapid growth and activity
  • Puberty phase - getting ready for reproduction
  • Tubulin proteins are formed which will make up the spindle, organelles are replicated, energy is stored up, and cytosol increases in volume
  • Balloon vs. shoe box demo
  • The Cell Cycle

    1. 1. The Cell Cycle How Cells Divide and Grow
    2. 2. Humble Beginnings  Every living thing on earth starts as a single cell
    3. 3. All Cells Have a “Life Cycle”• Includes periods of growth, rest & replication• Can be short (minutes) or long (years)• Different cell types have very different cycles
    4. 4. Cells Divide for Different Reasons• To replace old/worn out cells (red blood cells)• To repair injured tissues or combat illness• To reproduce (create another entire organism)
    5. 5. Three Types of Cell Division Binary Fission • Used by prokaryotes (unicellular: bacteria) • Fast & simple: every 20 – 30 min. Mitosis • Used by eukaryotic, somatic cells (body) • Much more complex • Highly regulated Meiosis • Even more complicated (cells divide twice) • Used by eukaryotic germ cells (reproductive)
    6. 6. Binary Fission in Prokaryotes Bacteria only have 1 chromosome • A single strand of DNA • Circular in shape
    7. 7. Binary Fission in Prokaryotes DNA duplicates • Two circular DNA strands move apart • Cell doubles in size
    8. 8. Binary Fission in Prokaryotes DNA moves to opposite ends of cell Cell membrane grows inward Cell wall grows from membrane materials & pinches cell in two
    9. 9. Binary Fission in Prokaryotes Two new cells are formed • Identical genetically (same DNA) • Cytoplasm contents vary
    10. 10. Types of Cell Division Binary Fission • Used by prokaryotes (unicellular: bacteria) • Fast & simple: every 20 – 30 min. Mitosis • Used by eukaryotic, somatic cells (body) • Much more complex • Highly regulated Meiosis • Even more complicated • Used by eukaryotic germ cells (reproductive)
    11. 11. Cell Cycle in Eukaryotes Interphase • Longest stage • 90% of cell’s life • G - no division 0 • 3 checkpoints: • G – gap 1 1 • S - synthesis • G – gap 2 2 Mitosis • 4 stages • Cytokinesis completes the cycle
    12. 12. Interphase – G1 (1st Gap or Growth phase)  Cell Growth • Organelles replicate • Cell volume doubles  Cell does its job • Normal metabolic processes  Longest phase  Some cells stay here permanently  G1 checkpoint • Is cell big enough? • Environment good?
    13. 13. Interphase – S (Synthesis phase)  Chromosome Replication • Loose bundles of chromatin • All DNA in nucleus copied resulting in… • Two identical strands of each chromosome • Sister chromatids joined by centromere
    14. 14. Interphase – G2 (2nd Gap or Growth phase)  More growth • Cell volume increases  G2 Checkpoint • DNA mistakes? • Cell volume OK? • Environment good?  Shortest phase
    15. 15. Mitosis4 Stages: • Prophase • Metaphase • Anaphase • Telophase
    16. 16. Mitosis - Prophase DNA coils & condenses (like thread on a spool) to form distinct chromosomes Nuclear membrane disappears Spindle fibers form out of centrosomes (2 centrioles ea.)
    17. 17. Metaphase Spindle fibers attach to kinetochores on the centromeres Chromosomes line up at the equatorial plane (middle) of the cell Mitotic spindle checkpoint • Are all chromosomes lined up? • Are they all attached to spindle fibers?
    18. 18. Anaphase Spindle fibers shorten, pulling sister chromatids apart Chromatids are drawn to opposite ends (poles) of the cell Centromere connections are cut
    19. 19. Mitotic Spindle Microtubules of the spindle attach to kinetochores on ? chromosomes Sister chromatids are pulled apart by ? spindle fibers Other unattached spindle fibers push against one another to elongate (stretch out) the cell
    20. 20. Telophase Chromosomes reach the poles New nuclear membranes form around chromatids Chromosomes unwind to become thread-like chromatin again Nucleolus forms
    21. 21. Cytokinesis The cytoplasm is evenly divided New cell membrane forms in animal cells New cell wall is built across for plant cells
    22. 22. Cytokinesis in Animal Cells Microfilaments assemble around cell middle Actin& myosin microfilaments form a ring around cell ATP (energy) used to squeeze cell in half
    23. 23. Cytokinesis in Plant Cells Rigid cell wall can’t just be squeezed in half Golgi apparatus sends vesicles filled with cell wall building materials to center Cell plate forms at equatorial plane Cell wall fills in gaps, cleaves cell in two
    24. 24. Interphase – G0 (pre-growth or resting phase) Mitosiscreates two identical daughter cells that go on to enter Interphase • Some enter G 1 and divide again • Some enter G0 - a rest phase where they do their job
    25. 25. Mitosis summarizedEukaryotic(plant &animal)Somatic (non-reproductive)Regulated bycheckpointsPMAT:ProphaseMetaphaseAnaphaseTelophase
    26. 26. Week 11 Lab ReviewMicroscope Lab: onion root tip mitosis
    27. 27. Cell Cycles vary by Type of Cell  Nerve, liver & muscle cells • Most stay in G0 (never divide) • Some divide only after years, if there are injuries • Brain & spinal chord injuries are often permanent because of this Skin, hair, eye, cheek & intestinal lining cells • Exposed to more wear & tear than other cells • Replaced every 1 - 35  Red blood cells (hemoglobin) days • Most rapidly dividing • Formed from bone marrow stem cells cells in humans • Never divide once formed • Die & replaced after ~ 4 months
    28. 28. Cancer - Cell Cycle out of Control Cancer cells • Tumors result from rapid, out of control cells dividing • Bypass normal G1, G2 and/or mitotic spindle checkpoints • Sloppy cell division = big trouble  Lack of quality controls • More mutations • Disorganized/deformed cells • Signal proteins lost/changed • Contact inhibition lost
    29. 29. Your Turn… What is binary fission? What type of cells use this process? Draw and label the cell cycle…include G1, S, G2, M and cytokinesis…what happens at each stage? What are the stages of Mitosis? What disease is associated with unregulated mitosis?