1. The Cell Cycle & Cancer Questions we will try to answer
1. What is cancer?
2. How are cancerous cells different than normal cells?
3. How do you get cancer?
i.e. What makes normal cells become cancer cells?

2. What is cancer? Cancer is … Cancer cells cannot stop dividing
Cell cycle

3. Fig 8.7

4. The Events of the Interphase
Divided into 3 phases:
G1 –
S –
G2 –

5. Length of G1 can vary greatly:

6. Cell Division or “M” phase
Cell Division consists of two parts
1. Mitosis:
2. Cytokinesis:
What needs to happen to the chromosomes prior to Mitosis?
During mitosis?

7. Fig 8.6

8. Sketch of one duplicated chromosome
Each chromatid has one DNA molecule
Sister chromatids
How do sister chromatids compare genetically?
What happens to sister chromatids during mitosis?
Centromere

9. S-Phase: DNA Replication
Mitosis: sister chromatids separate
Two-chromatid
chromosome
One-chromatid
chromosome
One-chromatid
chromosome
S-Phase: DNA Replication
Interphase

10. Mitosis: Division of the Nucleus
Four Stages:
Prophase –
Metaphase –
Anaphase –centromeres break and the chromosomes (now single chromatids) migrate to opposite poles
Telophase – nuclear envelope forms around each cluster of chromosomes

11. Fig 8.8

13. Cytokinesis: division of the cytoplasm to create 2 new cells

14. Fig 8.9

15. Produces somatic (body) cells
Mitosis
Produces somatic (body) cells
Meiosis
produces gametes
Fig 8.14

16. Normal Karyotype of Human Chromosomes
How many pairs of chromosomes in this Karyotype?
Paired chromosomes are homologous
How do you inherit chromosomes?
What gender?
Sex vs. autosomal chromosomes?

17. Sex chromosomes determine a person’s gender
Humans have 46 chromosomes:
Sex chromosomes:

18. Diploid cell: 6 total chromosomes, 3 sets of homologous chromosomes
Haploid cell
Haploid cell
One set of non-homologous
chromosomes
One set of
non-homologous
chromosomes

19. Regulation of Cell Division
What evidence in your own life do you have that cell division is regulated by your body?
What normally controls cell division?

20. Contact Inhibition
Cells do not normally grow or divide when in contact w/ other cells

21. Contact inhibition does not occur in Cancerous Cells
Cancerous cells continue growing and moving when they touch other cells.

22. Fig 8.10

23. Cell cycle control

25. Growth factor binds to receptor
Growth control in a normal cell
Signaling cell
Growth factor =
Growth factor binds to receptor
Receptor sets off a signal
cascade to nucleus
target cell enters
S-phase and divides,
eventually repairing wound
target cell
Nucleus

26. Several ways to get faulty growth control in a cancer cell
2. Mutant receptor might
turn on even without
binding growth factor
Signal cascade
might occur even
without trigger
from receptor
1. Cell might produce its own growth factor

27. The genetic basis of cancer (p.224-227 in Ch 11)
Proto-oncogenes:
Oncogenes:
genes that cause cancer
Oncogenes are rarely inherited.....Why?

28. Tumor Suppressor Genes
One mutant Tumor Suppressor Gene does not cause cancer....Why?

29. Fig

30. BRCA 1: Breast Cancer Susceptibility Gene
BRCA 1 is ….
If a women inherits a mutant BRCA 1 she has a
80 to 90% chance of developing breast cancer
Why aren’t the percentages 100%?
Why are the percentages (10%) much lower for the average woman?

31. Environmental causes of cancer
Viruses
Chemicals
Radiation
**All can cause mutations in tumor-suppressor genes and proto-oncogenes

32. Characteristics of all cancer cells
Immortal
Altered cell membranes
Have lost the genetic ability to stop dividing
Cancer is heritable:
Are dedifferentiated
No contact inhibition
If not treated will eventually cause death

33. Cancer treatment: Attack Actively Dividing Cells
Three treatments for cancer:
Surgery
Radiation
Phase-specific chemotherapies

34. Phase-specific Chemotherapies
Prevent cells from entering the S-phase
Block the S phase
Block or stop mitosis

35. But chemotherapy can’t discriminate between cancer cells and normal cells….
May affect all rapidly dividing cells
Which cells divide rapidly?
So.... what would be the side effects?

36. Side Effects of Chemotherapy

37. How to lower your Cancer Risks
Eat plenty of fiber
Fiber speeds passage through digestive tract
Do not smoke
Drink alcohol in moderation or not at all
Exercise regularly
Do not become overweight
Limit dietary fat
Limit sun exposure or use sunscreen
Learn to recognize the warning signs of cancer

38. Common Warning Signs of Cancer: C.A.U.T.I.O.N.
C - change in bowel or bladder habits
A - a sore that does not heal
U - unusual bleeding or discharge
T - thickening or lump in the breast or any part of the body
I - indigestion or difficulty swallowing
O - obvious change in a wart or mole
N - nagging cough or hoarseness

39. Down Syndrome - Incidence with Mother’s age
1 in 1000 births in U.S.
1 in 12 births for moms that are 50 years old
Most frequent genetic cause of mental retardation
I.Q. =

40. Down Syndrome as function of mother’s age – Fig 8.23

41. Human Somatic Cells have 46 Chromosomes
How many chromosomes in human gametes?

42. Down Syndrome
Meiosis

43. Down Syndrome Karyotype
What is wrong with the Karyotype?
Why are most trisomies fatal? (except sex chromo’s)

44. What if gametes were made by mitosis?
Human Life Cycle
Meiosis
What if gametes were made by mitosis?
Fig 8.14

45. Fig 8.15

46. Fig 8.16 Meiosis I

48. Stages of Meoisis Interphase – Meiosis I Prophase I – Metaphase I –
Anaphase I –
Telophase I –
Meiosis II
Prophase II – chromosomes attach to spindle
Metaphase II – chromosomes align at equator
Anaphase II – sister chromatids separate
Telophase II – cells divide, end result = 4 haploid daughter cells

49. Normal Meiosis Interphase diploid 2n
How do the chromo’s align at metaphase I?
What separates at anaphase I?
How do the chromo’s align at metaphase II?
What separates at anaphase II? n n
Meiosis I
Meiosis II n n n n

50. Fig 8.17

51. Normal Meiosis followed by Fertilization
Meiosis I
Meiosis II
Product of
meiosis
Fertilization
Zygote
Normal sperm
Chromosomes:
Both daughter cells
have one copy of
each chromosome
Normal diploid
zygote

52. Genetic Basis of Down Syndrome:
Nondisjunction:
in Meiosis I: Or
In Meiosis II:

53. Fig 8.20

54. Age of Mom vs. Age of Dad
Why is the age of the mother, but not the father, correlated with the probability of having a child with Down Syndrome?

55. Egg formation in humans
Pre-egg cells present before girls are born -- about 1000 or so.
Pre-egg cells are stuck at metaphase I
Ovulation:

56. Mom’s Pre-egg Cells form Prenatally
Half of you was present inside your grandmother as a single cell inside your mom when she was a fetus.
At about 12 years, women start ovulating one egg each month for next 40 years.
So …..A 50 yr old woman has had her eggs sitting with chromosomes aligned in metaphase for over 50 years!
Nondisjunction is rarely seen with chromosomes larger than #20--Why? .

57. Why doesn’t the age of the father influence the rate of Down syndrome?
Sex cell formation in Males:

58. Genetic Screening for Down Syndrome
Can we detect D.S. before birth?
Amniocentesis: fetus located using ultrasound, needle inserted and amniotic fluid extracted
Fluid contains fetal urine and fetal cells from skin, respiratory tract, urinary tract
Make karyotype to detect abnormal chromosome numbers.
Not performed until 16th week of pregnancy

59. Chorionic Villus Sampling (CVS)
Catheter inserted vaginally and chorionic tissue removed
9-11 weeks after conception results of tests within days rather than weeks as in amniocentesis
But may be slightly riskier for fetus

60. Meiosis Causes Genetic Variation
1. Independent Assortment =
Thus maternal and paternal chromosomes are shuffled
223 or 8,388,608 different possibilities from each parent, then fertilization gives 70 trillion

61. Fig. 8.18

62. 2nd Reason for Genetic Variation
2. Crossing over
Result:

63. Fig 8.19