2. Remember – All Living Things are Made of Cells

3. Why Are Cells Small?
As cells get bigger, more of its cytoplasm is located farther from the cell membrane.
If a cell gets too big, it would take too long to get materials into the cell and too long to get waste out of the cell.
Smaller cells are more efficient!

4. Cell Division All cells come from other living cells.
You (and other living things) grow because your cells get bigger and your number of cells gets larger.
A single cell divides into two cells.
Two cells divide into four, etc.
Cells must also divide because old cells die and need new cells to replace them!

6. DNA vocabulary: Chromatid – one half of a duplicated chromosome.
Sister Chromatids – two identical chromatids
Centromere – region of the condensed chromosomes that looks pinched.
Telomere – ends of the DNA molecule.

7. Sister Chromatids & Chromosomes
Human somatic cells (any cell other than a gamete) have 23 pairs of chromosomes. – one from mom and one from dad.
homologous chromosomes - a pair of chromosomes
Copy of chromosome from mom
or dad
Chromosome made in S phase of
Interphase

8. The Cell Cycle
Cell cycle – regular sequence of growth and division that eukaryotic cells undergo.
Prokaryotic cells undergo binary fission
2 purposes = Growth and
Divided into three main stages:
Interphase – cell grows into its mature size, makes a copy of its DNA, and prepares for division.
Mitosis – one copy of the DNA is distributed into each of its daughter cells
Cytokinesis – the cytoplasm divides and organelles are distributed into the two new cells

9. Interphase
Interphase = growth phase of cell. It is divided into 3 phases:
G1 (gap 1) phase - the cell grows and makes proteins.
S (synthesis) phase - chromosomes replicate
G2 (gap 2) phase - cells continue to grow and make proteins
**At the end of interphase the cell has 2 full sets of chromosomes**

10. G1 – Growth Phase Cell doubles in size
Cell produces all of the structures it needs to carry out its functions
Think of this phase as the cell just living its normal life.

11. S – DNA Copying Cell makes a copy of its DNA (replication)
This happens because the new cell needs all of the directions for its function and survival.
Think of this phase as placing the DNA on a copy machine.

12. G2 – Preparation Cell prepares to divide
Cell produces structures needed for cell division
Think of this phase as the cell double checking everything it needs to divide.

13. Learning Checkpoint TRUE CELL CYCLE INTERPHASE D. All of the above
1. T/F: Interphase is usually divided into 3 phases: G1, S, G2.
2. The ________ is the regular sequence of growth and division that cells undergo.
3. ________ is the stage of the cell cycle where the cell grows to its mature size, copies it DNA, and prepare to divide.
4. Cells can not get too big because:
A. there is not enough DNA to support large cells
B. diffusion is too slow to provide for large cells
C. the surface area of a cell increases too fast for the cell membrane to meet its needs.
D. all of the above
5. DNA is replicated during: A. interphase
B. prophase
C. metaphase
D. cytokinesis
CELL CYCLE
INTERPHASE
D. All of the above
A. Interphase

15. Regulation of the Cell Cycle
Cell cycle is controlled by a chemical control system that starts & stops events in the cell cycle.
External Regulation– signal that comes from outside of the cell; Ex. Hormone, nutrients, etc.
Internal Regulation– signal that comes from the nucleus; Ex. DNA inside of the cell

16. Checkpoints
Checkpoint – critical point where “stop” & “go” signals can regulate the cycle.
Note: Cell division is mostly in the “off” position in animal cells if there is no stimulus present.

17. Apoptosis Apoptosis – programmed cell death.
Internal / external signals activate genes that produce self-destructive enzymes.
Nucleus shrinks and breaks apart.
Ex: Web fingers & toes during development
Fetus Image: © Lunar Caustic 2007
Toes Image: © Cursedthing 2007

18. Cancer Cancer – uncontrolled cell division
Happens when the regulation of the cell cycle breaks down.
Cancer cells divide much more often than healthy cells do.
Leads to the formation of tumors
Tumors – clumps of cells that divide uncontrollably

19. Tumors There are 2 types of tumors:
Malignant – cancer cells can breakaway from the tumor & be carried to other parts of the body/organs & form more tumors
Metastasize = spread of disease from one organ to another.
Benign – abnormal cells typically remain clustered together.
It may be harmless & easily removed
Brain tumor image: © Eric Lewis 2001

20. Causes
Often the result of exposure to carcinogens = cancer causing agents (chemicals that can cause cancer)
Ex. UV rays, tobacco smoke, X-rays, etc.
Carcinogens mutate DNA
Other random mutations and some infectious agents can also cause cancer (Ex. HPV)