1. The Cell Cycle

2. Why do cells need to divide?
Cells are limited in size because the outside (the cell membrane) must transport food and oxygen to the parts inside.
As a cell grows, the volume of the cell increases at a faster rate than its surface area.

3. Surface Area & Volume Changes

4. Why would a cell want to be small?
As cells grow too large, they become inefficient.
Cells that grow too large do not have enough surface area to take in nutrients and remove waste.
Cells that grow too large take longer to move material within the cell.
Small cells have more efficient transport systems because they have a higher surface to volume ratio, S/V.

5. Cell Cycle Eukaryotic Process ONLY
Unicellular organisms: asexual reproduction
Multicellular organisms: growth and repair
Rate of cell cycle (speed of cell division) may differ depending on:
Type of cell
Age of cell
Other factors such as
Infection by a virus
Exposure to radiation, drugs, alcohol, smoke, or other toxins

6. Type of Cell
The function of the cell & type of tissue often determine the rate of its cell cycle
Fastest include: intestinal, skin, bone marrow, hair
Slowest: bone, liver, kidney
skin
bone
small intestine

7. External Factors Factors outside of the cell or
organism can affect the cell cycle.
Cells are exposed to many environmental factors that can directly influence the control and regulation of the cell cycle
These factors disrupt the cell cycle and can cause cells to divide uncontrollably, resulting in cancerous tumors. These factors are called carcinogens.

8. Genetic Factors
Some mutations to genes can result in changes to the cell cycle.
The BRCA1 gene can cause
breast cancer
Progeria is a genetic disorder
marked by rapid aging

9. Why can’t organisms live forever?
Cells cannot grow and divide indefinitely.
At the end of chromosomes are small ‘caps’ called telomeres that help keep the DNA from uncoiling. Every time the DNA is replicated, a piece of the telomere is lost. When the telomere is gone, the DNA can no longer replicate and the cell dies.
Many aging-related diseases are linked to shortened telomeres.
People with longer telomeres tend to live longer than people with shorter telomeres.

10. The Cell Cycle Occurs in 3 phases Interphase: preparation for division
Mitosis: nuclear division
Cytokinesis: cell division

11. INTERPHASE Longest phase of the cell cycle Marked by 3 distinct stages
Gap 1 (G1): Cell growth & replication of organelles (1st Checkpoint = Cell large enough & suitable environment)
Synthesis (S): DNA replication
Gap 2 (G2): Growth & preparation for cell division. (2nd Checkpoint = DNA correctly replicated)

12. What is G0? Resting phase where certain cells
leave the cell cycle and stop dividing
Some cells, once formed, remain in G0 for the life of the organism. These cells cannot be replaced once damaged.
Examples: Nerve and Muscle
Some cells enter an extended period of G0 , however, can be replaced overtime.
Examples: Liver and Kidney

13. MITOSIS M Phase: Process that divides the nucleus with replicated DNA
Approximately 15% of cell’s life cycle
4 Stages
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE

14. Prophase Nuclear membrane disintegrates Nucleolus disappears
Chromatin (containing replicated DNA) condenses into chromosomes
Centrioles begin to move apart
Spindle forms

15. Metaphase Chromosomes attach to spindle fibers
Chromosomes line up along equator of cell
(3rd Checkpoint - Are chromosomes aligned?)

16. Anaphase Spindle fibers shorten
Chromatids (daughter chromosomes) separate and move to opposite poles

17. Telophase Chromatids (daughter chromosomes) reach poles
Nuclear membrane reforms
Nucleolus reappears
Chromosomes decondense back into chromatin

18. Cytokenesis Follows mitosis
Plant Cells: Cell plate forms, dividing daughter cells
Animal Cells: Cleavage furrow forms & pinches cell into daughter cells

19. Cell Cycle Checkpoint 3 Are chromosomes aligned? Cytokinesis
Checkpoint 2: Has DNA replicated correctly?
Checkpoint 1: Is cell
getting too large ?