1. AP Biology
Ch. 12
The Cell Cycle

2. Limits to Cell Growth: Why do cells need to divide?
The larger a cell becomes, the more demands the cell places on its DNA.
The cell has “DNA overload”, and the needs of the growing cell can no longer be met.
The more trouble a cell has moving enough nutrients and wastes across the cell membrane.

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

4. Ratio of Surface Area to Volume in Cells
Cell Size
Cell Size
Surface Area (length x width x 6)
Surface Area
(l x w x 6)
Volume
(l x w x h)
Surface area to
Volume ratio

5. Cell Division
Before it becomes too large, a growing cell must divide into two “daughter” cells. This is cell division.
Before cell division occurs, the cell copies its DNA. This ensures that each daughter cell gets a complete set of genetic information.
Division increases the cell’s surface area to volume ratio.

6. Overview: Key Roles of Cell Division
Cell Division plays several important roles in the life of an organism:
1. Reproduction (unicellular organisms)
2. Allows multicellular organisms to reproduce
3. Cell and tissue renewal and repair
Passing identical genetic material from existing cells to new cells

7. Reproduction: An amoeba is dividing into two cells.
Each new cell will be an individual organism.

8. Growth and Development: A sand dollar embryo shortly
after the fertilized egg divided, forming two cells.

9. Tissue renewal: These dividing bone marrow cells will
give rise to new blood cells.

10. Cellular Organization of the Genetic Material
Cell division involves the distribution of identical genetic material—DNA—to two daughter cells.
A cell’s genetic information is called its genome.
When cells divide, the DNA is packaged into chromosomes.
Chromosomes are made of DNA, which carries the cell’s coded genetic information, and proteins.

11. Chromosomes
Cells of each organisms have a specific number of chromosomes.
Human somatic cells (body cells) have 46 (23 pairs)
Reproductive cells, or gametes, have 23 chromosomes.
Chromosomes are not visible except during cell division.
Each chromosome consists of two identical “sister” chromatids that are attached at the centromere.

12. Eukaryotic chromosomes: Chromosomes are visible within the nucleus as
the cell prepares to divide.

14. Cell Division A. The Cell Cycle B. Events of the Cell Cycle C. Mitosis
1. Prophase/Prometaphase
2. Metaphase
3. Anaphase
4. Telophase
D. Cytokinesis

15. The Cell Cycle
During the cell cycle, a cell grows, prepares for division, and divides to form two new daughter cells.
Interphase is the period between divisions, and includes G1, S, and G2 phases.
The M phase follows interphase, and includes mitosis and cytokinesis.

16. Concept Map Cell Cycle Section 10-2 includes M phase (Mitosis)
Interphase
is divided into
is divided into
G1 phase
S phase
Prophase
G2 phase
Metaphase
Telophase
Anaphase

17. Interphase Interphase takes much longer than actual cell division.
G1: Cells do most of their growing. Cells increase in size and synthesize new proteins and organelles.
S: DNA is copied
G2: Cell prepares for mitosis, makes organelles and structures needed for cell division

18. Figure 10–4 The Cell Cycle Section 10-2 G1 phase M phase S phase
Go to Section:

19. INTERPHASE

20. Mitosis
Following the events of Interphase, the cell will begin to divide. This is mitosis.
Biologists divide mitosis into four phases: prophase/prometaphase, metaphase, anaphase, and telophase

21. Prophase The first and longest phase of mitosis is prophase.
During prophase, the chromatin condenses to form chromosomes.
The centrioles separate, and a spindle begins to form.
The nuclear membrane begins to break down.

22. PROPHASE

23. Prometaphase Nuclear envelope fragments
Microtubules extend from each centrosome toward the middle of the cell.
Microtubules attach to the kinetochores, moving the chromosomes

24. PROMETAPHASE

25. Metaphase The stage following prophase is metaphase.
During metaphase, the chromosomes line up across the center of the cell.
Each chromosome is connected to a spindle fiber at its centromere.

26. METAPHASE

27. Anaphase Following metaphase is anaphase.
During anaphase, the sister chromatids separate into individual chromosomes and are moved apart.
The chromosomes form groups near the poles of the spindle.
Anaphase ends when the chromosomes stop moving.

28. ANAPHASE

29. Telophase The fourth and final stage of mitosis is telophase.
The chromosomes gather at opposite ends of the cell, and lose their distinct shapes.
Two nuclear membranes begin to form.

30. TELOPHASE

31. Cytokinesis
Cell division is not complete until cytokinesis occurs. Cytokinesis is division of the cytoplasm.
In animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two equal parts. A cleavage furrow forms.
In plants, a cell plate forms midway between the divided nuclei. The cell plate gradually develops into a separating membrane.

32. Cleavage furrow in animal cells

33. Cell plate forming in plant cell

38. Binary Fission
Prokaryotes such as bacteria reproduce by binary fission.
Most genes are carried on a single bacterial chromosome.
During binary fission, a bacterial chromosome replicates and the two daughter chromosomes move apart.

39. BINARY FISSION

40. Evolution of Mitosis
Since prokaryotes came before eukaryotes, it is likely that mitosis evolved from prokaryotic cell division.
Certain protists exhibit cell division processes that seem somewhere between bacterial binary fission and mitosis in eukaryotic cells.

41. Evolution of Mitosis?

42. Regulating the Cell Cycle
A. Controls on Cell Division
B. Cell Cycle Regulators
1. Internal Regulators
2. External Regulators
C. Uncontrolled Cell Growth

43. Cell Cycle Regulators
Cyclins regulate the timing of the cell cycle in eukaryotic cells.
Proteins that respond to events inside the cell are called internal regulators.
Proteins that respond to events outside the cell are called external regulators.

45. Cyclins and CDK
Most of the kinases that activate the cell cycle are present at a constant concentration in the cell, but most are in the inactive form.
Kinases (CDK) must be attached to a cyclin to become active.
Cyclin levels rise during the S and G2 phases, and falls during the M phase.
MPF (maturation promoting factor) level rises with the rise in cyclin concentration, causing the cell to go past the G2 checkpoint into M phase.

46. Does PDGF stimulate the division of human
fibroblasts in culture?

47. HUMAN FIBROBLASTS

48. Density-dependent inhibition
Cultured cells normally divide until they form a single layer of cells on the inner surface of the culture container, at which point they stop dividing.
This is known as contact inhibition, or density-dependent inhibition.

50. Uncontrolled cell growth
Cancer cells do not respond to the signals that regulate the growth of most cells. They have been transformed from a normal cell to a cancer cell.
A defect in a gene called p53 has been found in many types of cancer cells.
They continue to grow out of control, and can form masses of cells called tumors.

51. Benign vs. Malignant tumors
Tumors can damage surrounding tissues.
If the abnormal cells remain at the original site, the tumor is BENIGN and can usually be surgically removed.
If the tumor invades other organs and impairs their function, the tumor is MALIGNANT.
The spreading of cancer cells is METASTASIS.

52. BREAST CANCER

53. BREAST CANCER CELL

54. NORMAL
MAMMOGRAM
CANCEROUS
MASS