1. Cell Cycle and Cell Division

2. Objectives
What problems does growth cause for cells? What factors control cell growth?
Why do cells divide? What factors control cell division?
What are the phases of the cell cycle? What is each for?
Describe the processes that occur in each stage of cell division (mitosis).
Compare and contrast plant and animal cell division.
How does cell division in prokaryotes differ from eukaryotes?
Why do chromosomes form?
How many chromosomes are in each cell before and after cell division?
What is cancer?

3. What problems does growth cause for cells?
Objective #1
What problems does growth cause for cells?

4. Cell Size Limits (Part A)
Cells grow until they reach their maximum size limit. Then they must divide or die.
Unfortunately, everything the cell needs to take in or get rid of must leave through the cell membrane, which is proportional to the cell’s surface area.

5. Cell Size Limits (Part B)
As a cell grows, surface area does not grow as fast as volume.
At some point, the cell’s needs are too great to be met by diffusion through its cell membrane. That is the cell’s maximum size limit.
Cell Size (Length of a Side)
Cell Volume
(Needs)
Cell Surface Area
(Ability to Meet Needs) 1 6 2 8 24 3 27 54 4 64 96 5
125
150
216 7
343
296
Cell DIES!!

6. Cell Size Limits (Part C)
Cellular communications also limit the maximum size of a cell.
In a cell’s normal activities, signaling proteins, raw materials, and enzymes must diffuse through the cell’s cytoplasm to get to areas where they are needed.
If the cell gets too big, then these materials move too slowly to be used in the reactions needed to keep the cell alive.

7. Summary #1
When a cell grows, a much greater demand is placed on the limited amount of DNA. The instructions for making proteins can’t be used fast enough. This is called DNA overload.

8. Volume increases much faster than surface area.
Summary #2
Volume increases much faster than surface area.
Surface area to volume ratio decreases, which means eventually there is not enough cell membrane to do the job.

9. Summary #3
The space inside the membrane is too great; thus the cell cannot efficiently move materials within the cell.

10. Objective #2
Why do cells divide?

11. The process a cell undergoes in order to replace aging or dying cells.
Cell Division
The process a cell undergoes in order to replace aging or dying cells.

12. Cell division helps to…
Reduce the volume to increase the import/export of materials
Reduce the volume to more easily move materials within the cell
Minimize DNA “overload”

13. What are the phases of the cell cycle?
Objective #3
What are the phases of the cell cycle?

14. The Cell Cycle
Stages or phases:
Interphase
Mitosis
Cytokinesis

15. Interphase (G1 phase) “Growth 1” = making proteins and organelles
(“inter” = between)

16. Interphase (S phase) “Synthesis” = replication
(sister chromatids form)

17. Interphase (G2 phase) “Growth 2”
= making more organelles and fulfilling cell’s function
(until maximum SA:V)

18. Length of Cell Cycle Varies depending on type of cell.
If cell cycle took 12 hours:
G1:5 hrs
S: 4.5 hrs
G2: 2 hrs
M: 0.5 hrs
*Which stage does the cell spend most of it’s time?

19. Objective #4
Describe the processes that occur in each stage of cell division (or mitosis).

20. Mitosis begins…Prophase
“pro” = before
chromosomes form
nucleus breaks up
centrioles appear
spindle fibers form

21. Which of these is in prophase?D B E C

22. Mitosis: Metaphase “meta” = after or next in line
Spindles attach to chromatids
Centromeres align at middle

23. Which of these is metaphase?D B E C

24. Mitosis: Anaphase “ana” = leading up to… chromatids separate
chromatids pull to opposite ends of the cell

25. Which of these is in anaphase?D B E C

26. Mitosis: Telophase “telo” = end 2 new nuclei form
Coiled chromosomes change back to relaxed chromatin
Mitosis ends

27. Which of these is in telophase?D B E C

28. Cytokinesis
Cytoplasm and cell contents divide as cell membrane moves inward to create 2 daughter cells – each with its own nucleus & identical DNA

29. Other pictures of mitosis

30. Other pictures of mitosis

31. Other pictures of mitosis

32. Other pictures of mitosis

33. Other pictures of mitosis

34. Other pictures of mitosis

35. Compare & contrast cell division in plant and animal cells.
Objective #5
Compare & contrast cell division in plant and animal cells.

36. Animal cell mitosis

37. Plant cell mitosis

38. Cytokinesis differs…
CELL PLATE

39. TOTD
A scientist is observing an animal cell with a microscope. She notices that the chromosomes are becoming visible. Which phase of the cell cycle is the cell MOST likely entering into?
Prophase
Interphase
Metaphase
Anaphase

40. Compare cell division in prokaryotes (bacteria) and eukaryotes.
Objective #6
Compare cell division in prokaryotes (bacteria) and eukaryotes.

41. Prokaryotic Cell Division
Replication: copy the DNA*
Cell splits in half, called binary fission
3. This is a form of asexual reproduction
*Each cell has identical DNA copy

42. Eukaryotic Cell Division
Replication
Mitosis: chromosomes are assembled, sorted, and divided up through a series of phases
Cytokinesis: cytoplasm divides
* Each cell has an identical DNA copy

43. Why do chromosomes form?
Objective #7
Why do chromosomes form?

44. Chromosome Structure…
DNA is usually in the form of chromatin. (very loose strands)
Chromatin is made of DNA that is coiled around proteins called Histones and organized into groups called Nucleosomes
Chromatin continues to condense as the cell prepares for replication

45. Chromosome structure…
Before the cell divides, the super-condensed chromatin is duplicated as sister chromatids.
Sister chromatids are like matched socks and are held together by a Centromere
This forms homologous chromosomes

46. To handle the amount of DNA
Cells organize the DNA into chromosomes – condensed colored bodies that can be sorted during cell division.

47. How many chromosomes are in each cell before and after cell division?
Objective #7
How many chromosomes are in each cell before and after cell division?

48. Mitosis = diploid to diploid
Diploid means: The somatic (body) cell contains two copies of each chromosome. In humans we have 46 chromosomes. There are 23 chromosomes you get from Mom and 23 chromosomes you get from Dad. 46 46
S phase 92
Mitosis 46
When a somatic cell divides each new daughter cell must have the same amount of DNA. That’s the purpose of Replication and Mitosis.

49. What factors control cell division?

50. Control of the Cell Cycle
Cells require growth factors to divide (cyclins or hormones)
Cells need room to grow - if it’s cramped, no division
Cells normally stop dividing if they lose their anchorage

51. Objective #9
What is cancer?

52. Apoptosis Programmed cell death
Apoptotic cells shrink in size, break into smaller pieces that other body cells recognize and eat
For tissue development
To remove damaged cells
To destroy viral infected cells
To balance mitosis rate

53. What is Cancer? Disease of defective apoptosis
Cyclins and CDK (cyclin dependent kinases) control transition from G1 to S and G2 to M. If these don’t work properly it leads to…
tumor growth
“Mitosis gone mad”

54. Cancer causes
Mutated genes (called oncogenes) can over-stimulate cell division
Mutated tumor supressor genes fail to prevent tumor growth
*Mutagenic factors (mutation producing) include radiation, some foods, drugs & chemicals, viruses & microbial agents, smoke, dust like asbestos, inhalants, gasoline, lead…

55. Healthful Decisions to reduce Cancer Risk
Avoid carcinogens! (smoking)
Eat whole foods (fresh fruit and grains)
Exercise regularly to boost immune system
Don’t drink alcohol in excess
Don’t get sunburned or overexpose your skin to UV (watch out tanning bed victims)
Undergo regular screening and self-examination