Transcript Cellular Reproduction

Cellular Reproduction
(Eukaryotes)
Biology - Chapter 9
Pages 244-257
Warm-up:
1. How would you describe the process by
which organisms increase in size?
2. Are the cells of a small plant smaller or
larger than those of a large plant?
3. Why do cells stay small?
http://www.cellsalive.com/howbig.htm
What we will learn in Chapter 9:
- Living things grow by producing more cells.
- Cells produce other cells by dividing.
- The process by which a cell divides into
two new daughter cells is called cell
division.
Why must cells divide? Why don’t they
just grow bigger?
Three Reasons Why Cells Divide:
1. Growth
2. Replace
3. Repair
The key factor that limits the size of a cell is the
ratio of its surface area to its volume.
plasma membrane
cytoplasm and its contents
the structure through which
all nutrients and waste
products must pass.
By remaining small, cells have a higher ratio of surface
area to volume and can sustain themselves more easily.
On your own, calculate the volume of surface area to volume
for each of the cells below. Explain why it is best for cells to
remain small. (see pages 244-245)
4 um
1 um
2 um
-Once a cell reaches its size limit, it either stops
growing or it divides.
THE CELL CYCLE:
- the series of events that cells go through as they
grow and divide.
- During the cell cycle, a cell
- grows
- prepares for division
- divides into two daughter cells
which each begin the cycle
again.
Three Main Stages of The Cell Cycle:
(See page 246, Figure 9.3)
I. Interphase
II. Mitosis
III. Cytokinesis
I. Interphase:
-
The phase in which a cell spends most of its
life. There are three sub-stages:
1. G1 (Gap 1) – cell grows and
performs normal functions.
2. S (Synthesis) – cell replicates its DNA in
preparation for cell division.
3. G2 (Gap 2) – cell takes inventory to
make sure it is ready to continue on to
mitosis.
II. Mitosis:
Stage in which the cell’s nucleus and nuclear
material divides and separates to opposite
ends of the cell.
FOUR STAGES OF MITOSIS:
1.
2.
3.
4.
Prophase
Metaphase
Anaphase
Telophase
1. Prophase:
• First stage of mitosis.
• Stage of mitosis in which a dividing cell spends
the most time.
• Chromatin condenses into chromosomes:
sister chromatids
chromosome
centromere
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter
11/animations.html
2. Metaphase:
• Shortest phase of mitosis.
• Chromosomes attach to mitotic spindles (aka.
spindle fibers) and align along the equator of
the cell.
3. Anaphase:
• Microtubules shorten moving chromosomes
to opposite poles and the chromatids are
pulled apart.
4. Telophase:
• Chromosomes reach poles of cell and begin to
relax or de-condense.
• Nuclear envelope reforms.
• Nucleolus reappears.
• CELL IS ALMOST DONE DIVIDING!
III. Cytokinesis:
• Cell pinches inward at “equator” until the cell
divides into two daughter cells with identical
nuclei.
• In animal cells, this happens at the cleavage
furrow (formed during cytokinesis).
• In plant cells, instead of pinching, the cell
plate is formed.
Prophase
Cleavage Furrow
(animal cells)
Cell Plate (plant cells)
On-line Onion Root Tip Lab
• http://www.biology.arizona.edu/Cell_BIO/acti
vities/cell_cycle/36m.html
• GIVE IT A TRY!!!
Cell Cycle Regulation
• The timing and rate of cell division are important for
cells to develop normally.
• Proteins called CYCLINS and CDK enzymes control the
cell cycle.
• These proteins take action at certain checkpoints to
make sure the cell cycle is functioning properly. If
errors are found, often they are repaired.
• http://nobelprize.org/educational_games/medicine/
2001/
Cancer: Abnormal Cell Cycle
• Cancer is the uncontrolled growth and division
of cells.
• Caused by mutations in the regulatory genes
that were not repaired during the cell cycle at
the checkpoints.
• NIH Student Activities
Cancer Genetics
• More than one change in DNA is required to
change an abnormal cell into a cancer cell.
• This could explain why cancer runs in some
families. These changes cause a person to
have a predisposition for cancer.
Apoptosis: (programmed cell death)
- This “death program” can become activated
and cause a cell to shrink, shrivel and die in a
controlled manner.
- Examples:
- the fetal development of a human hand/foot
(webbed).
- Cell’s DNA damaged beyond repair.
- Leaves of deciduous trees fall during autumn.
Stem Cells:
• Unspecialized cells that can develop into
specialized cells when placed under the right
conditions.
• 2 Types:
– Embryonic stem cells (ethical concerns)
– Adult stem cells (not as controversial)
Stem Cell Research is Underway:
•
•
•
•
•
Alzheimer's,
cerebral palsy,
paralysis,
diabetes,
and people who suffer damage to their heart
after a heart attack.
Binary Fission