1. The Cell Cycle

2. 1. Cell Size Cells are limited in their size.
Female Egg - largest cell in the human body; seen without the aid of a microscope
Most cells are visible only with a microscope.

3. Growing Pains
The cytoplasm (volume) of a cell increases faster than the cell membrane (surface area.)

4. Need to Split
The cell membrane is needed to transport molecules such as food and waste in and out of the cell.
The cell must divide to increase the ratio of surface area to volume.
DNA in a large cell is “overloaded.”

5. Roles of Cell Division Unicellular organisms Multicellular organisms
Method of reproduction
Multicellular organisms
Growth
Maintenance
Replacement

6. Cell Cycle
The orderly sequence of cell growth and division that occurs in a cell
One cycle spans from the beginning of one cell division to the beginning of the next cell division.

7. Stages Interphase (normal cellular activity) Mitotic Phase/M Phase
G1 (growth)
S (DNA replication)
G2 (preparation for cell division)
Mitotic Phase/M Phase
Mitosis (nuclear division)
Cytokinesis (division of cytoplasm)

8. Cell Cycle

9. I need to rest…… Cells often pause in G1 before continuing.
Some cells, such as muscle and nerve cells, move into a resting phase known as G0.

10. What are the two main phases of the cell cycle?
includes
M phase
(Mitosis)
Interphase
is divided into
is divided into
G1 phase
S phase
Prophase
G2 phase
Metaphase
Telophase
Anaphase

11. Mitosis (Nuclear Division)
Mitosis is considered nuclear division since the steps only refer to the contents of the nucleus.
There are 4 steps.
Prophase P
Metaphase M
Anaphase A
Telophase T

12. Chromatin
During interphase, DNA and protein can be found in the nucleus in the form of chromatin.

13. Chromosomes
When the cell enters mitosis, chromatin coils up into the form of chromosomes.

14. Two Copies
Due to DNA replication in the S phase, each chromosome has an identical copy.

15. Sister Chromatids Each copy is called a chromatid.
Together, they are referred to as sister chromatids.
A centromere joins the sisters chromatids together.

16. Prophase The nucleus disappears DNA Condenses
The chromatid pairs (sister chromatids) are joined by a centromere.
The thread-like spindle fibers appear.
The centrioles move toward the poles.

17. Metaphase Sister Chromatids attach to spindle fibers
Chromatid pairs line up along the equator (middle) of the cell.
Why does this occur?
So that each new cell will receive one chromatid from the pair.

18. Anaphase
The chromatid pairs separate and the separated chromosomes move in opposite directions.
The spindle fibers contract and pull them toward the poles.

19. Telophase The cell begins to separate.
Two new nuclei begin to reappear.
Chromosomes uncoil to form chromatin.
The spindle fibers disappear.

20. Cytokinesis Division of the cytoplasm
Final separation into 2 new daughter cells
In plants, a cell plate forms to create a cell wall between the two new cells.

21. Twinsies
Each cell has its own nucleus with identical DNA—same number, same type
If a cell containing 46 chromosomes undergoes mitosis, how many chromosomes does each of its daughter cells contain? 46
Where did the extra 46 chromosomes come from?
The S phase of the cell cycle.

22. Control of the Cell Cycle
Growth-regulating genes provide instruction and checkpoints along the cell cycle.
Many cells also control their division through contact inhibition. When cells come into contact with other cells, signals are sent to halt division.

23. Mistakes
A malfunction of the growth-regulating genes can disrupt the cell cycle.
When cell division is out of control, a tumor may form.

24. Tumors A tumor is a dense mass of abnormal cells.
Benign tumors are localized and not life threatening.
Malignant tumors are more likely to be life threatening. The cells of malignant tumors invade other tissues.

25. Cancer
Cancer is a condition in which malignant cells invade and destroy body tissues.
Cancer develops over time due to a succession of genetic changes.
Carcinogens, which are cancer-causing agents, may also stimulate the disease.

26. Carcinogens Radiation Certain viruses Some chemicals X-rays
UV radiation
Sun
Tanning beds
Certain viruses
HPV
Some chemicals
Cigarette smoke

27. Cancer Cancer is the second leading cause of death in the US
The number 1 cause is heart disease
Cancer can affect any part of the body
Major killers are:
Lung
Colon
Breast
Prostate

28. Causes of Cancer Both environmental and genetics are involved
Cancer rates differ from country to country
Example: Breast cancer
High in the US
Low in Japan
Example: Stomach cancer
Common in China
Low in the US
When people move to another country their cancer rates follow those of the country they live in