1. Cell Growth & Division
Question:
Why do cells divide?

5. Why do we need to make more cells?
We start out as one cell!
We need to make more and more cells until we have
about one hundred trillion!

6. Q: Who has bigger cells?
A: Same cell size, RonRon has MORE!

7. Sea Urchin Cell Division
From One Cell to Many
Sea Urchin Cell Division

8. Why do we need to make more cells?

9. Why are we one hundred trillion SMALL cells and not one hundred LARGE cells?
Differentiation, replaceable
100,000,000,000,000 cells because....

10. They need to be small!

11. I. Why do Cells Divide?

12. A. Cells need to stay small because:
The larger a cell becomes, the more demands on its DNA
Trouble moving enough nutrients and wastes across the cell membrane
Organization!

13. DNA “Overload” DNA is the cell’s “library” of information.
Imagine a very large city using one local library for all materials

14. A big bag is weaker, harder to find things
Large cell, difficult to maneuver organelles

15. More volume = bigger need
The larger the volume of
the balloon, the weaker it
is. The balloon skin stays
the same.

16. Large surface area SPEEDS UP the movement of materials
B. What is Surface area?
The total area of the
surface of a three-
dimensional object
2 cm
What is the surface area of this cube?
2 cm
24 cm2
The villi of small intestines and the cristae of mitochondria are examples of maximizing surface area for chemical reaction and diffusion to take place
Large surface area SPEEDS UP the movement of materials

17. 200 cm3 C. What is Volume? The amount of 3-dimensional space
that an object occupies, “capacity”
Large volume SLOWS down
movement of materials
What is the VOLUME of the shape here?
200 cm3 cm

18. D. Ratio of Surface Area to Volume
As the length of cell increases,
volume increases faster surface area
(cm3 compared to cm2)
HIGH ratio desired: quick movement of materials
Ex: 6000/1 is better than 2/1

19. It’s better to have lots
of small cells
instead of fewer
large cells!

20. II. Chromosomes All genes located in DNA in nucleus of eukaryotic cell
B. Chromosomes
are condensed
forms of DNA

21. Chromosomes Chromosome number is unique to every species
Humans: 46 chr.
Chimpanzees: 48 chr.
Yeast: 32 chr.
Adders-Tongue Fern: 1440 chr.!

22. Anatomy of a Chromosome
Chromatids attached at
the centromere
Copied during
Interphase
D. After duplication
phase, each
chromosome
consists of two
identical “sister”
chromatids

23. II. Cell Division A.
46 chr 46
chromosomes
46 chr
B. Chromosome # stays the same
[Cells growths, doubles chromosomes, then splits, forming two daughter cells with original # of chromosomes]

24. C. Common Locations for Cell Division
Intestinal lining- every 24 hours
Skin
Blood cells/bone marrow- 120 days
Liver- sometimes

25. D. Cells that Rarely Divide (In G0 phase)
Muscle Cells
Cardiac cells
Kidney
Nerve cells

26. III. Cell Cycle

27. Gap0 “resting phase”, cell is not growing
A. Interphase: “I-ball”
90% of the time!
Gap “resting phase”, cell is not growing
Gap cell grows, doubles organelles
Synthesis duplication of the DNA in
the cell's chromosomes
Gap cell grows, microtubules assembled
G0- is “quiescent” phase.. Some cells stay here after terminal differentiation, while others are here and can move into G1

28. C. Checkpoints
G1 Checkpoint:
DNA to be replicated is healthy; cell size
G2 Checkpoint: Checks that DNA that was replicated is healthy; rest of cell ready for division
M checkpoint:
Chromosomes are properly attached to the spindle fibers.

29. What happens if the cell cannot pass through the checkpoint?
Repair the damage OR
B) Self-destruct: APOPTOSIS
(Programmed Cell Death)
There are proteins in the cell that regulate these processes and determine which way the cell will go.

30. Now entering “M Phase”..
First stop, Mitosis!

31. Prophase- “pasta” Chromatin fibers condense
Nuclear membrane breaks down
Spindle of microtubules forms from centrioles [animals only]
Attach to chromatids on centromere

32. Metaphase- “middle” Chromosomes line up in the middle
Spindle fibers attach centrioles to centromeres
Every sister chromatid has fiber attached to it
Centriole
Spindle

33. Anaphase: “away phase”, form “A’s”
Spindle fibers contract
Pull sister chromatids apart
The chromosomes continue to move until they are in two groups
Each side has own copy of DNA
Individual
chromosomes

34. Telophase- “end phase”
Nuclear membranes reform at each pole
Chromosomes unwind
Spindle disappears

35. Last part of “M Phase”..
Cytokinesis!

36. During cytokinesis, the cytoplasm cuts in half

37. Cytokinesis in Plants
In plants, a structure known as the CELL PLATE forms midway between the divided nuclei.

38. Cytokinesis in Animals
Animal cells contract an actin fiber across
middle of cell and “pinch” into 2 new cells- called
a “cleavage furrow”.

41. Twilight STUDIES IT TOO!

42. MITOSIS Video Daughter Parent Cell Cells
Why cant a cell just split into two?
Parent Cell to daughter cells- Note daughter cells look genetically identical to parent cells
DNA replication

43. V. Terms
A. Spindle: network of microtubules that move chromosomes during mitosis and meiosis
B. Equator: center line of cell where chromosomes line up during metaphase
C. Poles: the opposite ends of cell
D. Centrioles: animal cells only, move the spindle and chromosomes during division

44. E. Cleavage Furrow: the pinching in of animal cells during cytokinesis
F. cell plate: disk in plant cells that divide the cell into two daughter cells during cytokinesis
G. Centromere: region where two sister chromatids are joined tightly together

45. “Apoptosis”: programmed cell death

46. VI. Results of Mitosis A. Production of 2 new daughter cells
B. Daughter cells are exactly the same
as original parent cell
C. Cell --> Tissue --> Organ --> Organ
System --> Organism