1. Human body makes more than 20 billion new cells every day
Human body makes more than 20 billion new cells every day. Over the course of 7 years, all body cells have been replaced (except nerve cells).
How does your body make all these new cells?

2. Cell Cycle Notes
Cell Division — process by which a cell divides into 2 new cells
Why do cells need to divide?
Living things grow by producing more cells, NOT because each cell increases in size
Repair of damaged tissue
If cell gets too big, it cannot get enough nutrients into the cell and wastes out of the cell to maintain homeostasis

3. I. DNA – Deoxyribonucleic acid; located in nucleus
A. Long and thread-like DNA in a non-dividing cell – chromatin
B. Thick, short, coiled doubled DNA in a dividing cell – chromosome

4. chromosome consists of 2 parts:
a. chromatid
b. centromere – protein tab that holds 2 sister chromatids together

5. 2. chromosomes are divided into segments called – genes

6. coils up into chromosomes
C. Illustration: chromatin to chromosomes
duplicates itself
chromatin
coils up into chromosomes
Why does DNA need to change from chromatin to chromosome?
More efficient division

7. II. Cell Cycle – the repeating sequence of growth and
II. Cell Cycle – the repeating sequence of growth and division of a eukaryotic cell
A. The cell spends most of its time in – Interphase
1. Interphase: cell grows, DNA is loosely wound, and cell carries out normal functions

8. cell grows and matures – G1 (first growth)
2. 3 phases:
cell grows and matures – G1 (first growth)
chromatin duplicates – S (synthesis)
organelles replicate and cell prepares for division – G2 (second growth)
G1 phase
S phase
G2 phase

9. B. Division of the nucleus – mitosis

10. C. Division of the cytoplasm and organelles – cytokinesis
Occurs quickly
1. In animal cells the cytoplasm pinches in (Cleavage Furrow)
2. In plant cells a cell plate forms
Cell plate
D. After mitosis and cytokinesis, the cell returns to
Interphase

11. III. Mitosis – division of the nucleus into 2 nuclei, each with the same number and kind of chromosomes
A. HANDOUT

12. nuclear envelope breaking apart
Prophase
duplicated
chromosomes
nuclear envelope breaking apart
spindle fibers form

13. Metaphase
(middle)
spindle fibers
centriole

14. Anaphase
(away)
individual
chromosomes

15. nuclear envelope reforming chromosomes unwind into chromatin
Telophase
(two)
nuclear envelope reforming
chromosomes unwind into chromatin

16. Cytokinesis

17. Interphase
centrioles
nuclear envelope
chromatin

18. B. 4 phases PMAT
1. chromosomes condense, nuclear envelope breaks down, spindle fibers form – Prophase
2. chromosomes line up along equator -- Metaphase
3. chromatids separate, centromere divides, and move to opposite poles – Anaphase
4. chromosomes uncoil, new nuclear envelope forms spindle fibers break down – Telophase

20. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase
Cytokinesis D E F
Interphase
Metaphase
Prophase

21. 2 Daughter Cells Parent Cell
C. Mitosis occurs only in body cells, or – somatic cells
D. 2 new cells formed have same number and kind of chromosomes as original
1. original cell called – parent cell
2. cells formed are known as – daughter cells
2 Daughter Cells
Parent Cell

22. E. Many organisms, especially unicellular
E. Many organisms, especially unicellular organisms, reproduce by means of cell division--
called asexual reproduction ex: bacteria

23. Summary: Cell Cycle
Interphase Mitosis (PMAT) Cytokinesis
** Daughter cells genetically identical to parent cells

24. F. Chromosome Number
1. number of chromosomes each organism has in its cells varies from species to species
example: human = lettuce = dog = gorilla, chimp = 48

25. 2. all cells (except the sex cells) in an organism have the
2. all cells (except the sex cells) in an organism have the same number of chromosomes
example: human = 46
human skin cells = 46
human muscle cells = 46
human heart cells = 46

26. a. cyclins initiate the various stages of cell cycle
G. Regulating the Cell Cycle – not all cells move through cell cycle at the same rate
1. in eukaryotic cells, timing of the cell cycle is regulated by – proteins called cyclins
a. cyclins initiate the various stages of cell cycle

27. 2. cell cycle checkpoints -- regulate progress of cell cycle
a. ensure that damaged DNA not passed on to daughter cells
b. G1 checkpoint at end of G1 phase -- determines whether cell is ready to divide or not
c. G2 checkpoint at end of G2 phase – check if DNA replication finished
d. M checkpoint at Metaphase –
check for whether chromosomes
properly attached to spindle fibers

28. 3. injuries affect rate of cell division
a. cells at edge of injury stimulated to divide rapidly producing new cells
b. when healing is completed, rate of cell division -- slows down and returns to normal

29. 4. when cells come into contact with each other
4. when cells come into contact with each other in culture, they stop dividing

30. G. Uncontrolled Cell Growth
1. control over cell cycle can break down resulting in – cancer
2. cancer cells do not respond normally to – signals that regulate cell division
3. cells divide uncontrollably forming – tumors and can invade other tissues

31. 4. mutations in DNA leading to tumors can be caused by:
a. chemicals – smoking or asbestos (lung cancer)
b. radiation – sun -- UV rays (skin cancer)
c. viruses – HPV (cervical cancer) or hepatitis (liver cancer)
d. immune system disorders – HIV (many different cancers)
e. heredity – genetics

32. 3. p53 – “ guardian of the genome”
a. plays role in triggering control mechanisms at checkpoints -- suppresses tumors to prevent cancer
b. p53 can either – repair faulty DNA
or – kill off cell if it can’t be repaired (apoptosis)
c. problems with gene p53 -- related to more than 50% of all cancers

34. Chromosome Appearance & Location
Phase
Chromosome Appearance & Location
Important Events
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
DNA replication, cell grows and replicates organelles
DNA/chromatin copies itself
Nuclear envelope disappears, spindle fibers form
Chromosomes coil up
Chromosomes line up in the middle
Spindle fibers connect to chromosomes
Spindle fibers pull chromosome copies apart to opposite poles
Chromosome copies divide and move apart
Nuclear envelopes reform, 2 new nuclei are formed, spindle fibers disappear
Chromosomes uncoil back into chromatin
Division of the rest of the cell: cytoplasm and organelles
Chromatin