Transcript SNC2D – The Cell Cycle

SNC2D The Cell Cycle
Did you know?
In most eukaryotic cells, mitosis takes about 80
minutes. Embryonic cells can divide every 15-20
minutes! This varies between kingdoms (bacteria ~ 20
minutes), but is usually in the range of one to two
hours.
Check it out!
Review
• What is the difference between
chromosomes and chromatin?
• What is the name of the structure that joins
two sister chromatids together?
• How does the cell prepare for cell division
(mitosis)?
• What is the name of the phase that follows
mitosis?
Just to Clarify…
One Chromosome
One Chromosome
Centromere
Some questions for thought…
• How do cells decide what to do next?
• How do cells decide when to divide?
• How do you know whether you can
get into grade 12 or not? How do you
know whether you can go to
university/college or not?
• What conditions do you think must be
met before a cell can divide?
The Cell Cycle
• A continuous sequence of cell growth and division,
including the stages of interphase, mitosis, and
cytokinesis
• Take a look at Figure 1.28 on page 40
• The cell cycle is divided into two phases:
– Cell division (mitosis & cytokinesis)
– Interphase (cell is producing specific proteins,
growing, making more organelles, metabolizing, and
removing wastes)
Checkpoints
• Can you think of examples in everyday life that require
a checkpoint?
– Ticket taker at movie theatre
– Agent at border crossing
– Security check at airport
• Cells also have checkpoints!
Cell Cycle Checkpoints
• A point in the life of a cell when proteins determine
whether cell division should or should not occur
• Take a look at Figure 1.29 on p41 – when will the cell
cycle come to a halt?
• Cell division WILL NOT happen if:
– there is not enough nutrients to support cell growth
– DNA is not replicated
– DNA is damaged
How long do cells live?
Type of Body Cell
Brain
Red blood
Stomach lining
Liver
Intestine lining
Skin
Average Life Span
30-50 years
120 days
2 days
200 days
3 days
20 days
Cell death?
• What do you think causes cell
death?
• What do you think happens if
DNA is not copied properly? 
remember, the DNA sequence
of the copy must be the same
as the original (like a
photocopy)
– If you had to copy the
following sentence, “I love
Science” and made a
mistake… like this: “I hate
Science” then the idea has
completely changed (!)
Check it
out!!
Cell Suicide
• “Organized” cell death to reuse nutrients and materials
• Pre-programmed into cells (in genes)
• For example: aids proper development of finger and
toes in the fetus
When the checkpoints fail… Cancer may
happen
• Cancer cells show uncontrolled cell division because the
cell cycle is not regulated (starts with one cell)
• They divide faster than normal cells and form tumours
• Tumors result
• Example: Retinoblastoma in children
Cancer and the Cell Cycle
• Cancer can spread to other body parts (malignant) or can
be localized (benign)
• Read over figure 1.31 on p43  Watch this!
How do we treat Cancer?
• Cancer is often treated with chemotherapy
• These anticancer chemicals/drugs are applied to the
whole body via injection.
– kills rapidly dividing cancer cells or causes them to stop in
interphase
• Side Effects of Chemotherapy: hair loss, nausea,
weight loss, and weakness (fatigue)
• Chemotherapy chemicals also kill normal cells that
rapidly divide, such as intestinal cells and hair
follicles
DIFFERENCES BETWEEN CANCER CELLS AND
NORMAL CELLS
NORMAL CELLS
• Cell division is regulated by
special cell signals
• Cells divide into only one
layer of cells at a time.
• Cells have special functions
and serve a purpose. Cells
have different appearances.
• Cells require a certain
quantity of nutrients
• Cells stay in one place and
do not move from place to
place.
• Cells communicate with one
another.
CANCER CELLS
• Cell division is NOT regulated
by the cell signals. They
disregard the cell signals
• Cells divide into different
layers. No predetermined
number of divisions.
• Cells lose their special function
• Cells deprive normal cells of
nutrients and space.
• Cells have the ability to move
from place to place.
• Cells do not communicate with
one another.
Another commercial break…
• Fighting off tumours - Video
Homework
• Answer questions p45 #1,4,5
• Do Investigation 1-C p50 and answer #1-3
Q&A
• What is the main brain function?
– To coordinate between impulses and
responses (integrate signals coming from
sensory inputs)
• How many brain cells?
– 100 billion!
• Do brain cells regenerate?
– There are different cells that make up the
brain – glial cells do and it was recently
confirmed that neurons do as well but as you
age, this slows down