MITOSIS AND THE CELL CYCLE (Chapter 12) Preliminary concepts

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MITOSIS AND THE CELL CYCLE (Chapter 12) Preliminary concepts Powered By Docstoc
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     MITOSIS AND THE CELL CYCLE
             (Chapter 12)

Preliminary concepts:

--All cells arise from preexisting cells

--All cells reproduce by a cycle of
    duplication and division called the cell
    cycle

Why divide?

- reproduction (unicellular organisms)

- growth (zygote to multicellular organism)

- repair, renew (skin, bones, damage)
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OVERVIEW OF THE CELL CYCLE




   S Phase              Mitosis          Cytokinesis
(DNA Replication)   (Nuclear division)



  INTERPHASE            CELL DIVISION
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THE GENOME AND ITS CHROMOSOMES

Genome - a cell's total hereditary endowment
       (Its DNA)

Bacteria - usually one circle of DNA

Eukaryotes - much more DNA than bacteria

How much is lots of DNA?

Typical human cell - 3 meters of DNA
                (300,000 times cell diameter)

DNA is organized into CHROMOSOMES

HUMANS - 46 chromosomes -
     each -hundreds to thousands of genes

Chromosomes replicate during S phase

Chromosomes distribute during mitosis
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CHROMOSOME TERMINOLOGY
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Solution to Distribution Problem -MITOSIS

   coiling and shortening (PROPHASE)

   kinetochores form (PROMETAPHASE)

   organization - line up (METAPHASE)

   separation - (ANAPHASE)

   nuclei form (TELOPHASE)




Figure 12.5: MITOSIS

FIGURE 12-6: MITOTIC SPINDLE AT
             METAPHASE
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FIGURE 12-8: CYTOKINESIS -
             ANIMALS vs. PLANTS
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Notes to myself - not shown in class:

Interphase (G2):   chromosomes duplicated
                   chromosomes "loose"
                   centrosomes divided

Prophase:      chromatin fibers condensed
               can see sister chromatids
               microtubules push centrosomes

Prometaphase: nuclear envelope fragments
              microtubules join kinetochores
              nonkinetochore microtubules

Metaphase:     chromosomes aligned at
                   metaphase plate
               sister kinetochores opposite

Anaphase:      ~~MOVEMENT~~
               -chromosomes separate
               -move to poles

Telophase      daughter nuclei form
               chromatin uncoils
Cytokinesis    cytoplasm divides
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HOW DID MITOSIS EVOLVE?

Mitosis resembles bacterial cell division
           (Figure 12-10)
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       REGULATING THE CELL CYCLE

Examples of cell cycle regulation:

    -different cells divide at different rates

    -most cells do not divide most of the time

    -some cells (muscle, nerve) NEVER divide

     CANCER -unregulated cell division
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How is cell division regulated?

Hypothesis #1: each stage triggers the next

Figure 12-12 - Cell fusion experiment


Hypothesis #2: Cell cycle is controlled like
              a washing machine

Figure 12-13

CHECKPOINTS - places where cycle stops
        unless cell told to divide


Makes sense - most cells are NOT dividing

Default is NOT dividing

Most "resting" cells are arrested
in G1 (before S) - called G0
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CLASS - I did not get to cover the following so
it will not be on the test:

What is the mechanism leading to cell division?

  Two classes of proteins regulate the cell
         cycle - cyclins and kinases

Figure 12-14

This mechanism is linked to external cues to
          activate the cell cycle

Growth factors induce the cell cycle...



                 wound tissue



           platelets secrete PDGF



PDGF binds to PDGF receptor on fibroblast
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Stimulates fibroblasts to divide