1. Cell Growth and Division

2. Picture this unlikely scene: A huge cell moves through the city as its cilia propel it along. People run screaming as the cell’s flagellum flails along its side, smashing buildings. Proteins on the surface of the cell form a crude face with a sneer. People fear for their lives as the cell seeks food--or excretes waste!

3. Why couldn't a cell grow to the size of a city? Why do cells divide?

4. Why Cells Divide 1) DNA overload
Small cell – Information stored in DNA meets all the cell’s needs.
Huge cell -- Cell growth without limits leads to “information crisis.”
The DNA can’t keep up with the cell’s need for proteins.
DNA is the hereditary material of the cell. It is responsible for the production of all the proteins that determine the physical characteristics of an individual.

5. Why Cells Divide
2) The cell volume becomes too large for the surface area of the cell membrane to manage.
Exchange of materials (wastes, nutrients, gases) occurs through the cell membrane.
The rate of exchange depends on the surface area of the cell.
The rate at which nutrients are used and waste products are produced depends on the volume of the cell.

6. Ratio of surface area to volume
Why Cells Divide
Ratio of surface area to volume
As a cell increases in size, volume increases much more rapidly than surface area.
Ratio of surface area to volume decreases
Decrease in ratio causes problems for the cell

7. Ratio of Surface Area to Volume
As the length of a cell increases, its volume increases faster than its surface area. The resulting decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out.

8. Cell Division
To avoid decreasing the ratio of surface area to volume, cells divide before they become too large.
Each “daughter” cell has a greater ratio of surface area to volume than the “mother” cell.

9. Reality Check
The rate at which materials enter and leave through the cell membrane depends on the cell’s
a. volume.
b. weight.
c. mass.
d. surface area.

10. Reality Check The process of cell division results in
a. sister chromatids.
b. mitosis.
c. 2 daughter cells.
d. unregulated growth.

11. Why Cells Divide
Although a giant cell will never threaten a city, cells do come in a wide variety of shapes and sizes.

12. Some cells, such as RBC, measure only 8 um in diameter.
(the actual size of a red blood cell is approx 2 micron at the rim by 7 micron in diameter)

13. Other cells, such as nerve cells in large animals, can reach lengths
of up to 1 m,
but with small diameters.

14. The cell with the largest diameter is the yolk of an ostrich egg.
OF INTEREST
The cell with the largest diameter is the yolk of an ostrich egg.
The eggs are almost spherical in shape, about 6 inches long and equivalent in volume to about 20 hens' eggs.

15. Cell surface to volume ratio limits the size of a cell.
Reality Check
Why are the cells of a mouse and a blue whale almost exactly the same size?
Cell surface to volume ratio limits the size of a cell.
Cell surface to volume ratio limits the size of a cell.

16. Cell Reproduction
Cell theory—all cells come from pre- existing cells.

17. Cell Reproduction
Cell division is the process by which new cells are produced from pre- existing cells.
Each “daughter” cell gets an identical copy of the DNA and half of the cytoplasm and organelles.

18. Cell Reproduction--Prokaryotes
In Prokaryotes, cell division takes the form of BINARY FISSION
Bacteria have a single, circular DNA molecule with no proteins.
First, the DNA is copied (replicated)
Next, the cell splits into two equal, identical halves.

19. Cell Reproduction—Prokaryotes Binary Fission
Each half
gets one
chromosome
and half the
cytoplasm

20. Cell Reproduction—Eukaryotes
The cells of eukaryotes are much more complex--there is a nucleus and many organelles.
The genetic material in the nucleus must be copied and divided equally.
The organelles must be divided equally.

21. Cell Cycle and Mitosis
Genetic information that is passed from one generation to the next is carried by chromosomes.
Eukaryotic chromosomes are made up of DNA and protein.
Cells of every organism have a specific number of chromosomes.

22. Chromosomes are not visible in most cells except during cell division.
At the beginning of cell division, chromatin condenses into chromosomes.
Before cell division, each chromosome is copied.
Each chromosome consists of two identical sister” chromatids attached at a centromere.

23. Chromosomes Replicated chromosome Cell division separates chromatids.
Consists of 2 sister chromatids
Exact copies of each other
Connected by a centromere
Cell division separates chromatids.
Each new cell gets one copy of each chromatid.
This is a human chromosome shown as it appears through an electron microscope. Each chromosome has two sister chromatids attached at the centromere.

24. Reality Check
Genetic information that is passed on from generation to generation is carried by _______________
Chromosomes.

25. Reality Check Chromosomes are made up of _______________
DNA and proteins

26. Reality Check
Pairs of identical chromatids are attached to each other at an area called the
a. centriole.
b. centromere.
c. spindle.
d. chromosome.

27. The Cell Cycle
Eukaryotes undergo a life cycle known as the CELL CYCLE.

28. The Cell Cycle
The cell cycle is the series of events that cells go through as they grow and divide
During the cell cycle a cell…
Grows
Prepares for division
Divides to form two daughter cells

29. The Cell Cycle G1 – cell growth
S – chromosomes are replicated; DNA is copied
G2 – organelles and molecules required for cell division are produced
M – mitosis and cytokinesis
During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells.

30. The Cell Cycle Nucleus is copied, then the cell divides
(Mitosis) (cytokinesis)
Preparation for mitosis
During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells.
Cell growth
DNA is copied

31. The Cell Cycle
The length of the cell cycle depends on the type of cell and its environment.

32. The Cell Cycle
Brain cells, once formed, do not divide again--they stop in the G1 phase.

33. The Cell Cycle
RBC live about 120 days and are constantly replaced--each second about 2 million RBC are produced by cell division in the bone marrow.
Note the sickle cell.

34. Reality Check The cell cycle is the
a. series of events that cells go through as they grow and divide.
b. period of time between the birth and death of a cell.
c. time from prophase until cytokinesis.
d. time it takes for one cell to undergo cytokinesis.

35. Reality Check The two main stages of the cell cycle are called
a. mitosis and interphase.
b. synthesis and cytokinesis.
c. the M phase and the S phase.
d. cytokinesis and mitosis.

36. Reality Check Which of the following is a phase of the cell cycle?
a. G1 phase
b. G2 phase
c. M phase
d. All of the above

37. Reality Check
Which of the following is NOT a correct statement about the events of the cell cycle?
a. Interphase is usually the longest phase
b. DNA replicates during the S phase
c. Cell division ends with cytokinesis
d. The cell grows during the G2 Phase

38. Cell Cycle Part II

39. CELL CYCLE INTERPHASE M PHASE(Cell Division) G1 S G2
Mitosis-Division of Nucleus
Cytokinesis-Division of Cytoplasm

40. Interphase
The cell grows and replicates its DNA and centrioles.

41. Interphase

42. 4 Phases of Mitosis
Prophase
Metaphase
Anaphase
Telophase

43. Prophase Chromatin condenses into chromosomes Spindle begins to form
Nuclear membrane breaks down

44. Prophase

45. Metaphase Chromosomes line up across center of cell
Each chromosome is connected to a spindle fiber at its centromere.

46. Metaphase

47. Anaphase
Sister chromatids separate into individual chromosomes and begin to move to opposite ends of the cell.

48. Anaphase

49. Telophase --Chromosomes "uncondense" into chromatin.
--Two nuclear membranes reform.

50. Telophase

51. Cytokinesis Cytoplasm divides Organelles divide
2 Identical daughter cells are formed

52. I P M A T (I'LL PAY MORE ATTENTION TOMORROW) INTERPHASE PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

53. Cytokinesis in animal cells

54. Cytokinesis in animal cells

55. Cytokinesis in plant cells

57. Simplified Mitosis
Parent Cell
Two daughter cells

58. Stages of Mitosis

59. Reality Check The proper sequence of events in Mitosis is
a. Prophase/Anaphase/Metaphase/Telophase
b. Telophase/Anaphase/Prophase/Metaphase
c. Prophase/Metaphase/Anaphase/Telophase
d. Anaphase/Metaphase/Telophase/Prophase

60. Reality Check
During which phase of mitosis does the chromatin condense into chromosomes and become visible in the cell?
a. Telophase
b. Metaphase
c. Prophase
d. Anaphase

61. Reality Check
During which phase of mitosis do the chromosomes line up along the middle of the dividing cell?
a. Telophase
b. Metaphase
c. Prophase
d. Anaphase

62. Reality Check What is the role of the spindle during mitosis?
a. It breaks down the nuclear membrane.
b. It duplicates the DNA.
c. It divides the cell in half.
d. It helps separate the chromosomes.

63. Reality Check
When in mitosis does the nuclear membrane begin to break down?
a. Telophase
b. Metaphase
c. Prophase
d. It does not break down.

64. Reality Check What happens during cytokinesis?
a. The centrioles divide.
b. The cell grows.
c. The DNA is duplicated.
d. The cell divides.

65. C e l l D i v i s i o n
E n d