The Cell Cycle Control System by eddie5690

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									Chapter 12
Section 3
Cell Division
•The frequency of cell division varies with the type of cell
•Example: Human skin cells divide throughout your life.
  Liver cells divide only when need be.
•These cell cycle differences result from regulation at the
molecular level.
What controls the Cell?
•One hypothesis is that the cell cycle is driven by
specific signaling molecules present in the cytoplasm.

•Example: If one of the original cells was in the S phase
and the other in the G1, the G1 nucleus immediately
enters the S phase as though stimulated by chemical
present in the cytoplasm.
EXPERIMENT




RESULTS




   When a cell in the          When a cell in the
   S phase was fused           M phase was fused with
   with a cell in G1, the G1   a cell in G1, the G1
   nucleus immediately         nucleus immediately
   entered the S               began mitosis—a
   phase—DNA was               spindle formed and
   synthesized.                chromatin condensed,
                               even though the
                               chromosome had not
                               been duplicated.
 The Cell Cycle Control System
• Cell cycle control system- a cyclically operating set of
  molecules in the cell that triggers and coordinates key events in the
  cell cycle.

• Checkpoint- a control place where stop-n-go signals can
  regulate the cycle.
• G0 phase-a nondividing state occupied by the cells that have left
  the cell cycle.
• Density-dependent inhibition- a phenomenon in which
  crowded cells stop dividing.
• Anchorage dependence- the requirement that a cell must
  be attached to a substratum in order to divide.
Fig. 12-14
                       G1 checkpoint




                          Control
                          system       S
               G1



                      M       G2




M checkpoint
                    G2 checkpoint
   Fig. 12-15




                                        G0
G1 checkpoint




                  G1                             G1

(a) Cell receives a go-ahead   (b) Cell does not receive a
    signal                         go-ahead signal
Fig. 12-17

                 M      G1       S   G2   M        G1   S    G2    M      G1

                        MPF activity
                       Cyclin
                       concentration




                                          Time
             (a) Fluctuation of MPF activity and cyclin concentration during
                 the cell cycle




                                                                          Cyclin accumulation
                             Cdk


                Degraded
                cyclin
                                                   G2        Cdk
                     Cyclin is                  checkpoint
                     degraded

                                                              Cyclin
                                          MPF


             (b) Molecular mechanisms that help regulate the cell cycle
  Fig. 12-17a




      M         G1    S   G2    M   G1   S   G2    M      G1

                MPF activity
                Cyclin
                concentration




                            Time
(a) Fluctuation of MPF activity and cyclin concentration during
    the cell cycle
    Fig. 12-19




                 Anchorage dependence



                 Density-dependent inhibition



                 Density-dependent inhibition




                             25 µm                         25 µm

(a) Normal mammalian cells              (b) Cancer cells
• Cancer cells don’t follow the signals in the
  cell cycle.

• They continually divide and take over
  other tissues.

• If not treated they can kill the host.
• Cancer cells do not stop dividing when the
  growth factor is depleted.

• One hypothesis is cancer cells do not
  need growth factors to grow and divide.

• They make their growth factors
  themselves or have different signal
  pathways.
• Transformation is the process of a normal
  cell converting into a cancer cell.

• The immune system detects and destroys
  the cancer cell.

• If the cell doesn’t get destroyed it can form
  a tumor.
• If the cell do not move from their original
  place they can form a benign tumor.

• These tumors don’t cause much harm and
  can be surgically removed.

• A malignant tumor can impair the organ’s
  functions.
• Cancer cells have a abnormal surface.

• This allows them to lose attachment to
  neighboring cells and allows them to
  spread into nearby tissue.

• The spread of cancer cells to a distant
  location is called metastasis.
• A tumor that is localized can be treated
  with high-energy radiation.

• This only affects the cancer cells because
  they lost the ability to repair damaged
  cells.

• Chemotherapy is used to treat metastatic
  tumors.
• The reason we do not know much about
  cancer cells and the conversion of normal
  cells to cancer cells is that we don’t know
  much about normal cells function.
• If the cancer cell stops dividing, it will stop
  at random point in the cycle.

• If the cancer cell is given a continual
  supply of nutrients it can be “immortal.”

• Abnormal behavior of cancer cells can do
  a lot of damage inside a body.
                    Review!
1. Through a microscope, you can see a cell
   plate beginning to develop across the middle
   of a cell and nuclei re-forming on either side of
   the cell plate. This cell is most likely:

a.   An animal cell in the process of cytokinesis
b.   A plant cell in the process of cytokinesis
c.   An animal cell in the S phase of the cell cycle
d.   A bacterial cell dividing
e.   A plant cell in metaphase
                       B!
1. Through a microscope, you can see a
   cell plate beginning to develop across
   the middle of a cell and nuclei re-forming
   on either side of the cell plate. This cell is
   most likely:
     b. A plant cell in the process of
                   cytokinesis
2. Vinblastine is a standard chemotherapeutic drug
    used to treat cancer. Because it interferes with
    the assembly of microtubules, its effectiveness
    must be related to:

a. Disruption of mitotic spindle formation
b. Inhibition of regulatory protein phosphorylation
c. Suppression of cyclin production
d. Myosin denaturation and inhibition of cleavage
   furrow formation
e. Inhibition of DNA synthesis
                     A!
Vinblastine is a standard chemotherapeutic
   drug used to treat cancer. Because it
   interferes with the assembly of
   microtubules, its effectiveness must be
   related to:

a. Disruption of mitotic spindle formation
3. A particular cell has half as much DNA as
    some other cells in a mitotically active
    tissue. The cell in question is most likely
    in

a.   G1
b.   G2
c.   Prophase
d.   Metaphase
e.   anaphase
                      A!
A particular cell has half as much DNA as
   some other cells in a mitotically active
   tissue. The cell in question is most likely
   in

a. G1
4. One difference between cancer cells and normal
    cells is that cancer cells

a. Are unable to synthesize DNA
b. Are arrested at the S phase of the cell cycle
c. Continue to divide even when they are tightly
   packed together
d. Cannot function properly because they are
   affected by density dependent inhibition
e. Are always in the M phase of the cell cycle.
                    C!
•   One difference between cancer cells and
    normal cells is that cancer cells

c. Continue to divide even when they are
    tightly packed together
5. The decline of MPF activity at the end of
    mitosis is due to

a.   The destruction of the protein kinase Cdk
b.   Decreased synthesis of cyclin
c.   the degradation of cyclin
d.   Synthesis of DNA
e.   An increase in the cell’s volume-to-
     genome ratio
                     C!
The decline of MPF activity at the end of
   mitosis is due to

c. the degradation of cyclin
6. The drug cytochalasin B blocks the
    function of actin. Which of the following
    aspects of the cell cycle would be most
    disrupted by cytochalasin B?
a. Spindle formation
b. Spindle attachment to kinetochores
c. DNA synthesis
d. Cell elongation during anaphase
e. Cleavage furrow formation
                    E!
The drug cytochalasin B blocks the function
   of actin. Which of the following aspects
   of the cell cycle would be most disrupted
   by cytochalasin B?

e. Cleavage furrow formation
7. In the cells of some organisms, mitosis
    occurs without cytokinesis. This will
    result in
a. Cells with more than one nucleus
b. Cells that are unusually small
c. cells lacking nuclei
d. Destruction of chromosomes
e. Cell cycles lacking an S phase
                      A!
In the cells of some organisms, mitosis
  occurs without cytokinesis. This will result
  in

a. Cells with more than one nucleus
8. Which of the following does not occur
   during mitosis?

a.   Condensation of the chromosomes
b.   Replication of the DNA
c.   Separation of sister chromatids
d.   Spindle formation
e.   Separation of the spindle poles
                    B!
Which of the following does not occur during
  mitosis?



b. Replication of the DNA

								
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