Transcript Topic 2: Regulating the cell cycle

Unit 5
Topic 2:
Regulating the cell cycle
Growth factors: proteins secreted
by "control" cells to regulate the
cycles of other cells.
There are 50 known growth
factors.
M checkpoint: occurs during
metaphase; checks to see that all
sister chromatids are attached to the
appropriate centrosomes.
G2 checkpoint: "proofreading" and
repair of replicated DNA. When done,
signals a “go-ahead” into mitosis.
G1 checkpoint: if conditions are not
appropriate (missing essential
nutrients, not enough space, etc), the
cell will not move into S phase.
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Other factors that affect cell division:
Section 10-3
Anchorage dependence:
Many cells will divide only if they are attached to some kind of
surface (another cell, an organ lining, the wall of a petri dish)
Density Dependent Growth Inhibition
Cells will stop dividing when the run out of space!
Figure 8.8, p133
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What happens if cell cycle regulation
is not working properly?
• Sometimes cell DNA gets damaged and
that affects its ability to control the cell
cycle.
• Apoptosis
• Apoptosis 2
• Cancer
Two Types of Tumors
Benign
• Localized (does not
spread)
• Resemble normal
cells
• Grow more slowly
(yrs)
Malignant
• Metastasizes
(travels) by
spreading through
blood or lymph
• Look different than
normal cells
• Grow more quickly
(weeks/months)
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Why are tumors harmful?
Mutated cells…
• Can’t carry out normal functions
• Crowd out normal cells
• Steal nutrients from normal cells
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Cancer is always a genetic disease. Why?
Mutations can be inherited or environmentally caused.
Carcinogens - chemical, physical,
or biological agents that cause
cancer by mutating genes
•
•
•
•
UV radiation
Tobacco
Some viruses
Some chemicals
What types of genes do carcinogens
mutate?
Proto-Oncogenes
• Normally regulate
the cell cycle and
cell division
• Mutation turns them
into “oncogenes”
• Oncogenes turn
normal cells into
malignant ones
(uncontrolled growth
and division)
Tumor Suppressor
Genes
• Block cell growth
and division
• Mutation leads to
inability to stop cell
division
• Gene p53 on
chromosome 17 is
an example
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What does p53 do normally?
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Malignant cancer cells
Angiogenesis
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Malignant cancer cells
Are able to reproduce indefinitely (not
density-dependent)
Invade and metastasize
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Normal versus Cancerous
Fibroblast Cells
Fibroblast cells are found in connective tissue