Control of the Cell
Cycle
Ch. 12
Section 12.3
The Main Idea
• The Cell Cycle is regulated by a
molecular control system
How often do cells
divide?
• Different types of cells divide at different times
– Skin cells divide frequently
– Liver cel...
What drives the
cell cycle?
• Very specific
chemical signals in
the cytoplasm
control the cell cycle
• This hypothesis was...
The Checkpoints
• The signals in
the cycle are
transmitted via
signal
transduction
pathways
Quick Think

What controls the
cell cycle?
The CELL CYCLE
CONTROL SYSTEM
• A set of
molecules that
operate in a cycle
to trigger and
coordinate the
events of the cel...
The CELL CYCLE CONTROL
SYSTEM

• A good analogy is the timing device on a
washing machine
– Each step happens on it’s own
...
CHECKPOINTS in the
Cell Cycle Control
System
• A critical control
point in the cell
cycle where the
cycle stops until
a go...
The checkpoints
• The G1 checkpoint
seems to be an
especially important
one
– If the go-ahead signal is
received here, the...
There are 3 major
checkpoints
• G1 checkpoint
• G2 checkpoint
• M checkpoint
Quick Think

How do checkpoints
help regulate the cell
cycle?
The “chemicals” that
control the cell cycle
• 2 types of proteins:
– Cyclins
– Cyclin-dependent
kinases (Cdks)
• Remember ...
The “chemicals” that
control the cell cycle
• Cyclin levels rise a lot during interphase
• Cyclin levels fall quickly duri...
The “chemicals” that
control the cell cycle
• Peaks in the activity of cyclin correspond
to peaks in the activity of MPF
–...
MPF
• Triggers other
protein kinases
• Stimulates the
breakdown of the
nuclear membrane
• Triggers the
breakdown of
cyclin
Examples of other
cell cycle regulators
1. A signal in the M phase checkpoint ensures
that all the chromosomes are properl...
Quick Think

How do cyclins and
MPF help regulate the
cell cycle?
Cancer
• Cancer cells do not
respond normally to
the control
mechanisms
• These cells divide
excessively and
invade other ...
Cancer
• Cells turn cancerous when a
single cell undergoes a
transformation (the process
that converts a normal cell to a
...
Cancer
• A tumor that stays at the original site
forms a lump called a benign tumor
• These usually do not cause problems
...
Benign Tumors…Before &
After
Benign Tumors…Before &
After
Cancer
• Malignant tumors the cells become
invasive enough in
other tissues to
impair the functions
of organs
Cancer
• Cancerous cells also
become “loose” (lose
their attachment to
other cells) and are
carried into other
tissues in ...
Cancer
• Cancer cells are
abnormal in that:
– Odd number of
chromosomes
– Disabled metabolism
– Nonfunctioning
metabolism
...
Treatments for Cancer
• High energy radiation
• Chemotherapy
– Drugs that interfere with the cell
cycle
• Taxol prevents c...
Causes of Cancer
• There are many
• All causes involve the alteration of
genes that help control the cell cycle
AP Bio Ch. 12, part 2
AP Bio Ch. 12, part 2
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AP Bio Ch. 12, part 2

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AP Bio Ch. 12, part 2

  1. 1. Control of the Cell Cycle Ch. 12 Section 12.3
  2. 2. The Main Idea • The Cell Cycle is regulated by a molecular control system
  3. 3. How often do cells divide? • Different types of cells divide at different times – Skin cells divide frequently – Liver cells divide infrequently – Mature nerve and muscle cells do not divide at all • These differences are the result of regulation of these cells at the molecular level
  4. 4. What drives the cell cycle? • Very specific chemical signals in the cytoplasm control the cell cycle • This hypothesis was E.g. one cell in G1, while the other was in mitosis tested by fusing the The G1 cell would immediately nuclei of 2 cells – Each cell was in a different phase of the cell cycle enter mitosis – Seems to support the idea that chemicals in the cytoplasm of the cell in mitosis caused the G1 cell to also go into mitosis
  5. 5. The Checkpoints • The signals in the cycle are transmitted via signal transduction pathways
  6. 6. Quick Think What controls the cell cycle?
  7. 7. The CELL CYCLE CONTROL SYSTEM • A set of molecules that operate in a cycle to trigger and coordinate the events of the cell cycle
  8. 8. The CELL CYCLE CONTROL SYSTEM • A good analogy is the timing device on a washing machine – Each step happens on it’s own – Driven by an internal clock that tells it when to begin each new step – Regulated by both internal signals (tub is full of water) and external signals (pushing the start button)
  9. 9. CHECKPOINTS in the Cell Cycle Control System • A critical control point in the cell cycle where the cycle stops until a go-ahead signal is received
  10. 10. The checkpoints • The G1 checkpoint seems to be an especially important one – If the go-ahead signal is received here, the cell usually completes S, G2, and M phase – If not signal is received, the cell goes into G0, a non-dividing state
  11. 11. There are 3 major checkpoints • G1 checkpoint • G2 checkpoint • M checkpoint
  12. 12. Quick Think How do checkpoints help regulate the cell cycle?
  13. 13. The “chemicals” that control the cell cycle • 2 types of proteins: – Cyclins – Cyclin-dependent kinases (Cdks) • Remember a kinase is a protein that phosphorylates other molecules • These kinases are only active when attached to a cyclin protein
  14. 14. The “chemicals” that control the cell cycle • Cyclin levels rise a lot during interphase • Cyclin levels fall quickly during mitosis
  15. 15. The “chemicals” that control the cell cycle • Peaks in the activity of cyclin correspond to peaks in the activity of MPF – M-phase promoting factor – This protein bonds to cyclin & triggers the passage of the cell from the G2 checkpoint into mitosis
  16. 16. MPF • Triggers other protein kinases • Stimulates the breakdown of the nuclear membrane • Triggers the breakdown of cyclin
  17. 17. Examples of other cell cycle regulators 1. A signal in the M phase checkpoint ensures that all the chromosomes are properly attached to the spindle fiber 1. Helps ensure that there are no missing or extra chromosomes in the new cells 2. Another signal delays anaphase until all the until all the spindles are attached to the centrosomes 1. Once attached, another signal causes the proteins holding the sister chromatids together to break down
  18. 18. Quick Think How do cyclins and MPF help regulate the cell cycle?
  19. 19. Cancer • Cancer cells do not respond normally to the control mechanisms • These cells divide excessively and invade other tissues
  20. 20. Cancer • Cells turn cancerous when a single cell undergoes a transformation (the process that converts a normal cell to a cancer cell) • Normally, the immune system finds and destroys transformed Cancer cell cells (gray) being • Cells that are not destroyed may divide excessively and attacked by form a tumor - a mass of immune system abnormal cells cells (green)
  21. 21. Cancer • A tumor that stays at the original site forms a lump called a benign tumor • These usually do not cause problems and can be removed surgically Ready?…
  22. 22. Benign Tumors…Before & After
  23. 23. Benign Tumors…Before & After
  24. 24. Cancer • Malignant tumors the cells become invasive enough in other tissues to impair the functions of organs
  25. 25. Cancer • Cancerous cells also become “loose” (lose their attachment to other cells) and are carried into other tissues in the blood stream, where they start new tumors • This is called metastasis
  26. 26. Cancer • Cancer cells are abnormal in that: – Odd number of chromosomes – Disabled metabolism – Nonfunctioning metabolism – Secrete signal molecules that cause blood vessels to grow toward a tumor
  27. 27. Treatments for Cancer • High energy radiation • Chemotherapy – Drugs that interfere with the cell cycle • Taxol prevents cells from moving past metaphase • Many side effects due to the effect on normal cells • These treatments target cells that are dividing rapidly
  28. 28. Causes of Cancer • There are many • All causes involve the alteration of genes that help control the cell cycle

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