1. The Cell Cycle
10-2

2. The Cell Cycle
Process by which a cell grows, prepares for division and divides

3. The Cell Cycle Four phases G1 (Gap 1)
Cell grows, generates organelles, etc.
40% of a cell’s life
If a cell’s life were a day it would last from midnight to 9:36 am

4. The Cell Cycle S (Synthesis) All of a cell’s DNA is copied
39% of a cell’s life
If a cell’s life were a day it would last from 9:36 am to 6:47 pm

5. The Cell Cycle G2 (Gap 2) Final preparation for cell division
19% of a cell’s life
If a cell’s life were a day it would last from 6:47 pm to 11:21 pm

6. The Cell Cycle M (Mitosis) Cell division 2% of a cell’s life
If a cell’s life were a day it would last from 11:21 pm to midnight

7. The Cell Cycle Interphase G1, S and G2 phases
“Business as usual” for a cell
98% of a cell’s life
Basically the time a cell spends not dividing

8. Cell Division
Ends with two genetically identical daughter cells

9. Cell Division Before a cell divides:
An exact copy of the cell’s DNA is made
S phase of the cell cycle

10. Cell Division DNA condenses into chromosomes
Most of the time DNA is in a loose jumbled mess called chromatin
Resembles Ramen soup

11. Cell Division
Chromatin
cell membrane
chromatin
nucleus

12. Cell Division
If a cell divided before condensing there is no way to ensure each new cell received equal amounts of DNA

13. Cell Division Chromosomes
Made of two exact copies of the same section of DNA
Two copies are attached to one another
DNA is very tightly packed

14. Cell Division Chromosome structure wound around proteins identical
strands
attach
DNA
strand
DNA
condenses

15. Cell Division Chromosome structure Centromere: attachment point
Tightly
packed
DNA
Sister
chromatids:
two copies of the
same DNA

16. BREAK

17. Cell Division Two Phases: Mitosis: division of the nucleus
Cytokinesis: division of the cytoplasm

18. Cell Division Mitosis Division of the nucleus
If something goes wrong here the daughter cells may not function properly or they may die 

19. Cell Division machinery Chromosomes
Spindles: protein fibers that form then pull the chromosomes apart at the end of mitosis
Centroles: structures that help organize the spindles

20. Cell Division
4 Phases:
Prophase
Metaphase
Anaphase
Telophase
= PMAT

21. Cell Division Prophase
Chromatin (DNA soup) condenses into chromosomes (X-shaped structures)
Centrioles move to opposite ends of the cells
Spindle begins to form
Nuclear envelope breaks down

22. Cell Division
Prophase

23. Cell Division Metaphase
Chromosomes line up down the center of the cell
Spindles attach to the chromosomes
Nucleus has completely dissolved

24. Cell Division
Metaphase

25. Cell Division Anaphase
Sister chromatids (each half of the X-shaped chromosome) separate
Spindles pull sister chromatids apart

26. Cell Division
Anaphase

27. Cell Division Telophase
Chromosomes gather at opposite ends of the cell and begin to unravel into chromatin
Two new nuclear envelopes form

28. Cell Division
Telophase

29. Cell Division
Ends with one giant cell with two nuclei

30. Cell Division Cytokinesis In animal cells:
Cell membrane pinches inward between the two nuclei
Continues pinching until two nuclei are separated
End up with about half the organelles and cytoplasm in each cell

31. Cell Division
In animal cells:

32. Cell Division In plant cells:
A cell plate forms between the two nuclei
Cell plate turns into the new cell membrane
New cell wall forms around the cell membrane

33. Cell Division
In plant cells:
Cell plate

34. Cell Division
Cell division movie

35. BREAK

36. Control of the Cell Cycle 10-3

37. Enzymes that Control the Cell Cycle
Controlled in large part by a group of enzymes called cyclins
Cyclins: levels rise and fall during cycle causing numerous different actions
Other enzymes regulate specific phases of the cell cycle
Still more enzymes: respond to events outside the cell and adjust the cell cycle

38. Enzymes that Control the Cell Cycle
Production of these enzymes is directed by DNA
When DNA is damaged, production of enzymes goes all wrong:
Complete lack of production of a enzyme
Overproduction of a enzyme
Without the proper amount of specific enzymes the cell cycle will either stop (resulting in cell death) or cells will divide uncontrollably (resulting in cancer)

39. Contact Inhibition
Some cells will only divide if they are not in direct contact with one another
When skin cells contact one another, cell division slows to rates just fast enough to replace cells that die due to normal wear and tear
Skin cells sense contact through chemical signals, which are controlled by DNA
Damage to the DNA that controls these signals can also result in cancer

40. Cancer
Cancer: a disease where cells lose the ability to control the cell cycle
Caused by changes to the DNA that controls enzymes that regulate the cell cycle
Most small changes are fixed by the body, those that are not can become cancer
Can begin in any cells of the body and then spread through the body in the bloodstream or lymphatic system (glands)

41. Cancer
A quote from the American Cancer Society website:
“Cancer is the second leading cause of death in the United States. Nearly half of all men and a little over one-third of all women in the US will develop cancer during their lifetimes. Today, millions of people are living with cancer or have had cancer.
“The risk of developing most types of cancer can be reduced by changes in a person's lifestyle, for example, by quitting smoking and eating a better diet. The sooner a cancer is found and treatment begins, the better are the chances for living for many years.”

42. Causes of Cancer The well-known factors that increase risk:
Overexposure to UV radiation (THE SUN & SUN LAMPS!!)
Smoking
Over consumption of alcohol
Other forms of radiation
Contaminants in water
Viruses!

43. Scare the Girls Slides Cervical Cancer
Rates of cervical cancer have risen dramatically in young (16- to 30-year-olds) girls recently
Infection with human papilloma virus (HPV) is found in nearly 80% of all cases of cervical cancer
There are 3,700 fatalities in the U.S. each year due to cervical cancer
HPV is a sexually-transmitted disease!!!

44. Scare the Girls Slides Cervical Cancer
Routine screening (yearly gynecological exam) is the best way to catch the disease early.
Vaccines are now available (Gardasil and Cervarix) to protect against HPV but it must be administered before a girl becomes sexually active
There is no way to vaccinate or test males (who are carriers) and there is almost no way to tell whether a male is infected

45. Scare the Guys Slide
Testicular Cancer (aka “What Lance Armstrong had”)
Testicular cancer is the most common cancer in American men between the ages of 15 and 40 (YOUR AGE GROUP!).
7,600 men receive a diagnosis of testicular cancer each year in the US men die
When diagnosed early, testicular cancer is highly treatable
Regular testicular self-examinations can help identify dangerous growths early, when the chance for successful treatment is highest