Transcript Lecture #3 The Cell Cycle & Cancer

Lecture #3 The Cell Cycle &
Cancer
Unit 5: Cell Reproduction
Cell cycle- a repeating cycle of
cellular growth and division during
the life of an organism.
What’s the result?
• 2 daughter cells genetically
identical to the parent cell
they came from.
1.Interphase- composed of
G1, S, G2 stages
– This is the longest part of
cell cycle. A cell spends
90% of its time in
interphase.
2.M= Mitosis = Nuclear
division
G1 Phase - Cell Growth
• In the G1 phase, the
cell increases in size
due to rapid growth.
• Cells also synthesize
new proteins and
organelles.
S Phase: DNA Replication
– In the S (or synthesis)
phase, new DNA is
synthesized when the
chromosomes are
replicated.
– The cell has DOUBLE
the genetic material
at this point (sister
chromatids rather
than chromosomes)
G2 Phase: Preparing for Cell
Division
– In the G2 phase,
growth continues.
– The cell prepares for
cell division by
producing organelles
and molecules
required for cell
division.
M Phase
– In eukaryotes, cell
division occurs in two
stages: mitosis and
cytokinesis.
– Mitosis is the
division of the cell
nucleus.
– Cytokinesis is the
division of the
cytoplasm.
Regulating the Cell Cycle
• The cell cycle has key checkpoints at which feedback
can trigger the next phase of the cell cycle ( like a
green light).
• There are also feedback signals that can delay the
passage to the next phase (red light). This allows the
current phase to be completed.
• In other words, checkpoints CONTROL the rate of
cell division
These checkpoints are actually controlled by
a family of proteins called cyclins.
• Their job is to regulate the timing of the
cell cycle in eukaryotic cells.
Checkpoints
Cell Growth (G1) checkpoint – This checkpoint
makes the decision of whether or not the cell
will divide.
• If conditions are favorable, synthesis phase (S
phase) begins and the cells DNA is copied.
If conditions are NOT favorable, the cell will stop
division at this checkpoint.
Checkpoints (continued)
DNA synthesis checkpoint (G2) – DNA is checked
by DNA repair enzymes. If this checkpoint is
passed, proteins help to trigger mitosis.
Mitosis checkpoint ~ this checkpoint triggers
the end of mitosis. It indicates that the
new cell is in the initial growth phase (G1)
What do you think?
Do cells continue going through the cell cycle
forever………………………..????????????????
Apoptosis
Definition- the process of programmed cell death.
This is important for development, homeostasis
and elimination of pathogens and tumor cells
Example: the foot of a mouse is shaped the way
it is partly because the toes undergo apoptosis
during tissue development.
When Control is Lost
Sometimes, there may be a mutation on one of the
genes that regulates cell growth and division.
• This means that the proteins necessary to monitor
cell growth are absent.
Cancer - is a disorder in which body cells lose
the ability to control cell growth.
Cancer cells do not respond to the body’s
control mechanisms.
They may cause cell division to either speed up,
or to slow down.
• Either way, this is damaging to the organism
What causes mutations (defects in
genes) that can lead to cancer?
1. Mutations can arise spontaneously; meaning
that normal cells become cancer cells for no
apparent reason.
2. Other sources of gene defects are smoking
tobacco, radiation exposure, and viral infection.
What happens in your body if a cell
becomes cancerous?
Normally, your body’s immune cells destroy
cancer cells.
• Sometimes cancer cells can go undetected.
These cells can continue to grow and divide
and eventually will form a tumor.
Tumor ~ a mass of cancer cells within otherwise
healthy tissue.
Types of Tumors
1. Benign tumors ~ Tumors formed from a mass
of cells that remain at the original site that
cancerous growth began.
2. Malignant tumor ~ tumors that form if cancer
cells spread to and destroy healthy neighboring
tissues and other parts of the body.
Metastasis ~ the spread of cancer cells beyond their
original site.
Tumor treatment
1. Surgical removal (for localized tumors)
2. Chemotherapy ( poisonous chemicals)
3. Targeted radiation (high-energy radiation)
Chemotherapy and radiation are especially
harmful to actively dividing cells (both
cancerous and normal)
Most cancer drugs interfere with the cell cycle
of cancer cells.