1. Explain why cells are relatively small
Section 9.1 & 9.2 Objectives
Explain why cells are relatively small
Sequence the events of the cell cycle.
Explain the process of cytokinesis

2. Cell Size Limitations
Cells come in a wide variety of sizes and shapes.
Considering this wide range of cells sizes, why then can’t most organisms be just one giant cell?

3. Diffusion limits cell size
Although diffusion is a fast and efficient process over short distances, it becomes slow and inefficient as the distances become larger.
Because of the slow rate of diffusion, organisms can’t be just one giant-sized cell.

4. DNA limits cell size
The cell cannot survive unless there is enough DNA to support the protein needs of the cell.

5. Surface area-to-volume ratio
4 mm
4 mm
2 mm
2 mm
1 mm
1 mm
2 mm
4 mm
Surface area = 6 mm2 Volume = 1 mm3
Surface area = 24 mm2 Volume = 8 mm3
As a cell’s size increases, its volume increases much faster than its surface area
If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete.
The surface area, however, would increase by a factor of only four.
The cell would either starve to death or be poisoned from the buildup of waste products.

6. Cell Reproduction
Cell division is the process by which new cells are produced from one cell.
Cell division results in two cells that are identical to the original, parent cell.

7. chromosomes
Structures, which contain DNA and become darkly colored when stained, are called chromosomes.
Chromosomes are the carriers of the genetic material that is copied and passed from generation to generation of cells.
Accurate transmission of chromosomes during cell division is critical.

8. The large, complex chromosomes of eukaryotes duplicate with each cell division
Chromosomes contain a very long DNA molecule with thousands of genes
Individual chromosomes are only visible during cell division
They are packaged as chromatin
Before a cell starts dividing, the chromosomes are duplicated
This process produces sister chromatids
Sister chromatids
Centromere
Centromere

9. double-stranded human chromosomes
ready for mitosis

10. The Cell Cycle
The cell cycle is the sequence of growth and division of a cell.
The majority of a cell’s life is spent in the growth period known as interphase.
Interphase

11. The Cell Cycle
Following interphase, a cell enters its period of nuclear division called mitosis.
Following mitosis, the cytoplasm divides, separating the two daughter cells.
Mitosis

12. Interphase: A Busy Time
Interphase, the busiest phase of the cell cycle, is divided into three parts: G1,S, & G2
Interphase
DNA synthesis and replication
Rapid growth and metabolic activity
cell prepares for division

13. Interphase: A Busy Time
During the first part,(G1) the cell grows and protein production is high.
Interphase
Rapid growth and metabolic activity

14. Interphase: A Busy Time
In the next part of interphase, (S) the cell copies its chromosomes.
Interphase
DNA synthesis and replication

15. Interphase: A Busy Time
After the chromosomes have been duplicated, the cell enters another shorter growth period (G2) in which mitochondria and other organelles are manufactured and cell parts needed for cell division are assembled
Interphase
cell prepares for division

16. Biology is the only subject in which multiplication is the same thing as division…

17. MITOSIS: Making New Cells Making New DNA during S phase of interphase

18. Where it all began…
You started as a cell smaller than a period at the end of a sentence…

19. Getting from there to here…
Going from egg to baby….
the original fertilized egg has to divide…
and divide…

20. Why do cells divide… One-celled organisms Multi-celled organisms
for reproduction
asexual reproduction (clones)
Multi-celled organisms
for growth & development
from fertilized egg to adult
for repair & replacement
replace cells that die from normal wear & tear or from injury
amoeba
starfish
Unicellular organisms
Cell division = reproduction
Reproduces entire organism& increase population
Multicellular organisms
Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg
Also use cell division to repair & renew cells that die from normal wear & tear or accidents

21. The Phases of Mitosis PMAT
The four phases of mitosis are prophase, metaphase, anaphase, and telophase.
PMAT

22. Prophase: The first phase of mitosis
During prophase, the chromatin coils to form visible chromosomes.
Spindle fibers
Disappearing nuclear envelope
Doubled chromosome

23. Prophase: The first phase of mitosis
The two halves of the doubled structure are called sister chromatids.
Sister chromatids are held together by a structure called a centromere, which plays a role in chromosome movement during mitosis.
Centromere
Sister chromatids

24. Metaphase: The second stage of mitosis
During metaphase, the chromosomes move to the equator of the spindle.

25. Anaphase: The third phase of mitosis
During anaphase, the centromeres split and the sister chromatids are pulled apart to opposite poles of the cell.

26. Telophase: The fourth phase of mitosis
During telophase, two distinct daughter cells are formed. The cells separate as the cell cycle proceeds into the next interphase.
Nuclear envelope reappears
Two daughter cells are formed

27. DNA must be duplicated…
chromosomes in cell
4 single-stranded chromosomes
nucleus
cell
DNA in chromosomes
nucleus
cell
duplicated chromosomes
duplicated
chromosomes
4 double-stranded chromosomes

28. Mitosis: Dividing DNA & cells
Stage 1: cell copies DNA
Copy DNA!
DNA
cell
nucleus
(interphase)

29. Mitosis: Dividing DNA & cells
Stage 2: DNA winds into chromosomes
DNA is wound up into chromosomes to keep it organized
duplicated chromosomes
Wind up!
cell
nucleus
(prophase)

30. Mitosis: Dividing DNA & cells
Stage 3: Chromosomes line up
chromosomes line up in middle
attached to protein “cables” that will help them move
Line up!
duplicated chromosomes
lined up in middle of cell
(metaphase)

31. Mitosis: Dividing DNA & cells
Stage 4: Chromosomes separate
chromosomes split, separating pairs
start moving to opposite ends
Separate!
chromosomes split & move to opposite ends
(anaphase)

32. Mitosis: Dividing DNA & cells
Stage 5: Cell starts to divide
cells start to divide
nucleus forms again
Divide!
(telophase)

33. Mitosis: Dividing DNA & cells
Stage 6: DNA unwinds again
cells separate
now they can do their every day jobs
Bye Bye!
(cytokinesis)

34. New “daughter” cells Get 2 exact copies of original cells same DNA
“clones”

35. Cytokinesis
Following telophase, the cell’s cytoplasm divides in a process called cytokinesis.
Cytokinesis differs between plants and animals.
Toward the end of telophase in animal cells, the plasma membrane pinches in along the equator.

36. Cytokinesis
Plant cells have a rigid cell wall, so the plasma membrane does not pinch in.
A structure known as the cell plate is laid down across the cell’s equator
A cell membrane forms around each cell, and new cell walls form on each side of the cell plate until separation is complete.

37. Results of Mitosis
When mitosis is complete, unicellular organisms remain as single cells.
In multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function.
Tissues organize in various combinations to form organs that perform more complex roles within the organism.
Multiple organs that work together form an organ system.

38. Mitosis in whitefish blastula

39. Mitosis in plant cell

40. onion root tip

41. Overview of mitosis Please Make Another Two Cells I.P.M.A.T.C.
interphase
prophase
Please Make Another Two Cells
cytokinesis
metaphase
anaphase
telophase

42. Describe the role of enzymes in the regulation of the cell cycle.
Section 9.3 Objectives
Describe the role of enzymes in the regulation of the cell cycle.
Distinguish between the events of a normal cell cycle and the abnormal events that result in cancer.
Identify ways to potentially reduce the risk of cancer.

43. Mitosis & Cancer: When Making New Cells Goes Terribly Wrong!

44. When is mitosis a good thing?
When you have to add or replace cells
growth & development
repair
replacement

45. When is mitosis a BAD thing
When cells reproduce & they are not needed
these cells take over organs, but don’t do the right job
they just keep making copies
cancer
damages organs

46. Why would cells just make copies?
If DNA gets damaged, cells stop listening to correct instructions
mutations
Causes of mutations:
UV radiation
chemical exposure
radiation exposure
heat
cigarette smoke
pollution
age
genetics

47. Normal Control of the Cell Cycle
Proteins and enzymes control the cell cycle
The cell cycle is controlled by proteins called cyclins and a set of enzymes that attach to the cyclin and become activated.
Occasionally, cells lose control of the cell cycle.

48. Normal Control of the Cell Cycle
This uncontrolled dividing of cells can result from the failure to produce certain enzymes, the overproduction of enzymes, or the production of other enzymes at the wrong time.
Cancer is a malignant growth resulting from uncontrolled cell division.

49. Normal Control of the Cell Cycle
Enzyme production is directed by genes located on the chromosomes.
A gene is a segment of DNA that controls the production of a protein.

50. Cancer: A mistake in the Cell Cycle
Currently, scientists consider cancer to be a result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle.
Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients

51. Tumors Benign tumor abnormal cells remain at original site as a lump
most do not cause serious problems & can be removed by surgery

52. Tumors Malignant tumor cells leave original site
carried by blood system to other tissues
start more tumors
damage functions of organs throughout body

53. Cancer: A mistake in the Cell Cycle
In later stages, cancer cells enter the circulatory system and spread throughout the body, a process called metastasis, forming new tumors that disrupt the function of organs, organ systems, and ultimately, the organism.

54. Cancer: breast cancer cell & mammogram

55. The causes of cancer
The causes of cancer are difficult to pinpoint because both genetic and environmental factors are involved.
Environmental factors, such as cigarette smoke, air and water pollution, and exposure to ultraviolet radiation from the sun, are all known to damage the genes that control the cell cycle.
Cancer may also be caused by viral infections that damage the genes.

56. Cancer prevention
Physicians and dietary experts agree that diets low in fat and high in fiber content can reduce the risk of many kinds of cancer.
Vitamins and minerals may also help prevent cancer.
In addition to diet, other healthy choices such as daily exercise and not using tobacco also are known to reduce the risk of cancer.