1. Cell Division

2. Name that animal!

3. How do we go from embryo to fully-developed organism?
True or false: Organisms grow and get bigger solely because the cells get bigger.
False

4. Cells have an optimal size
If cells grow too large, they aren’t able to exchange materials efficiently.
Surface area : Volume
Cells like a lot of surface area and want a high SA:V ratio
More surface area/membrane allows for more chemical reactions and transport of materials (think cristae)

5. As the cell grows, the workload for the nucleus becomes too great.
DNA Overload
As the cell grows, the workload for the nucleus becomes too great.

6. The solution: Division
Rudolf Virchow: “Every cell from a cell.”
Multicellular organisms grow and develop from the division of cells.
Organisms repair themselves via cell division (cuts, bone fractures, torn ligaments, etc.)

7. Simple
Prokaryotes (bacteria) reproduce via a process called binary fission.
Leads to the creation of two identical cells.
Bacteria have one, circular chromosome and no nucleus
What needs to happen?
DNA needs to duplicate

8. Complex
Karyotype: the number and appearance of chromosomes in an organism Humans have 46 chromosomes (23 pairs- one from each parent) Chromosomes are condensed chromatin

9. Chromosome Structure Chromosomes store DNA and your genes
One duplicated chromosome is made of two sister chromatids held together by a centromere
Each sister chromatid on a chromosome is identical to each other (same size, shape, and same genes with same traits)
Homologous chromosomes have the same size, shape, and genes but different traits (you get one from mom and one from dad)

10. Mitosis: nuclear division
Process of dividing the genetic material in a cell for division
Start with one cell and end with two identical cells
Must create exact copies of original to maintain genetic continuity
Genetic continuity- keeping the same number of chromosomes (don’t want to gain or lose any)
Prophase Metaphase Anaphase
Telophase and then Cytokinesis

11. Prophase: 1st Phase Before Mitosis
Chromatin condenses into chromosomes
Centrioles appear and move to poles
Nucleolus disappears
Spindle fibers form
Before Mitosis

12. Prometaphase: transition to metaphase
Nuclear membrane breaks down
Kinetochore forms at each chromatid
Microtubules aka spindle fibers attach to kinetochores of chromatids

13. Chromosomes are moved to middle of the cell by the spindle fibers
Metaphase
Chromosomes are moved to middle of the cell by the spindle fibers

14. Sister chromatids separate and move towards opposite ends
Anaphase
Sister chromatids separate and move towards opposite ends

15. Chromosome movement
Microtubule shortens at kinetochore end rather that at centriole end.
Motor protein walks chromosome towards centriole in a process that requires ATP

16. Telophase: opposite of prophase
Chromatin condenses into chromosomes
Centrioles appear
Nucleolus and nuclear membrane disappear
Spindle fibers appear
Chromosomes spread out as chromatin
Centrioles disappear
Nucleolus and nuclear membrane reappear
Spindle fibers disappear

17. Telophase & Cytokinesis
Two nuclei appear
Cytoplasm splits into two cells
“Cytokinesis” = cell movement

18. Differences with Cytokinesis
Animal Cell
Plant Cell
Animal cells are pinched with a cleavage furrow (microfilament) that splits the cell in half
Cell wall prevents plant cells from pinching
Instead, a cell plate forms in the middle of the cell

19. Can the daughter cells divide again as they are?
Summary
Can the daughter cells divide again as they are?

20. Cell Cycle Mitosis is the shortest part of the cell cycle
The larger portion of the cycle is Interphase (nondividing) which consists of three phases
G1 – after mitosis, cell must make more organelles to perform functions
S – synthesis of DNA (single chromosome to duplicated)
G2 – cell makes more organelles & molecules to prepare for division
G0 – cell stops dividing (ex. Nerve cell)

21. Cell cycle regulation

22. Is it ideal for an organism’s cells to keep dividing forever?
Energy expensive
Not enough space
When should cells stop dividing?
Regulation

23. Cells stop growing when they contact one another
How would this apply to a cut?
Or to a developing organism?

24. CELL DIVISION GENES
EXAMPLE: Cell division genes can be ________ in case of injury.
Cells near injury are
stimulated to divide
to heal and replace damaged/missing cells
and shut off when the
repair has been made.
turned on

25. CELL DIVISION GENES Some cells divide frequently
(some human skin cells divide once/hour)
Some cells divide occasionally
(liver cells divide about once/year)
Some cells don’t divide once they form
(nerve cells)

26. CELL CYCLE REGULATORS
In early 1980’s scientists discovered a protein in dividing cells that caused a
______________to form in
_______________ cells
Mitotic spindle
NON-dividing

27. CELL CYCLE REGULATORS Levels of this protein rose and fell with
the cell cycle so it was named
__________ because it seemed to control the cell cycle.
A whole family of CYCLINS have since been discovered that regulate the _____________________
in EUKARYOTIC CELLS
CYCLIN
TIMING of CELL CYCLE

28. OTHER REGULATORS INTERNAL
______________ REGULATORS Proteins that respond to events inside
the cell.
Allow cell cycle to proceed only if
certain processes have happened
EX: Cell can’t enter mitosis until all the
chromosomes have been copied

29. Three Cell Cycle Checkpoints
1st checkpoint: at the end of G1 (checks that the cell has doubled in size)
2nd checkpoint: at the end of G2 (checks that the cell can divide)
3rd checkpoint: at the end of metaphase (checks to see that replicated chromosomes are attached to spindle fibers)

30. OTHER REGULATORS EXTERNAL
______________ REGULATORS Proteins that respond to events outside
the cell.
Signals tell cell to speed up or slow
down the cell cycle
EX:
Growth factors stimulate cells to divide Especially important during wound healing and
embryo development

31. EXTERNAL REGULATORS Molecules on the surface of neighboring
cells act as signals to slow down
or stop the
cell’s cycle.
These signals prevent
excessive growth and
keep tissues from
disrupting each other.

32. Cancer cells have lost control of their cell division genes
SEM Image by: Riedell
CHO (Chinese Hamster Ovary) cells in culture

33. NO CONTACT INHIBITION Cancer cells don’t stop when they touch nearby
they just keep growing!
That’s what makes
a tumor.
See a video

34. Cancer cells Carcinogens Don’t stop dividing
Like a “car with no brakes”
Can spread to new places (METASTASIS)
______________ are substances that can damage DNA and cause cancer
Ex: Cigarette smoke (OR CHEW), Radiation, chemicals in environment, even viruses,
Carcinogens

35. Cancer cells CELL CYCLE p53
Cancer is complicated and can have many causes, but all cancers have one thing in common . . .…
They have lost control over their _____________.
Many cancers cells have a damaged or defective
gene called _____, so they can’t respond to
normal cell signals to control their growth.
CELL CYCLE
p53