1. The cell Cycle and Cell Division
LS Chapter 3

2. The Cell Cycle Every organism begins as a single cell
In animals, including humans: sperm fertilizes egg
Fertilized egg is called a zygote
How, then, does the zygote become millions or trillions of cells?
Cells divide
1 cell becomes 2, which become 4, which become 8 and so on
Cells have a life of their own
They grow, develop, then divide
This is called the cell cycle

3. Phases of the Cell Cycle
IPMAT
Interphase
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

4. Interphase (Intermission)
The resting phase of the cell
Cells spend a majority of their lives in interphase
The growth and development stage
3 parts of interphase
G1 Phase (Gap phase 1)
Cell grows and functions as normal
S phase
DNA duplicates
The cell then has 2x as much DNA as it normally does
DNA is in disorganized
G2 Phase (Gap phase 2)
Cell grows again, and finishes duplicating organelles

6. Mitosis The period of nuclear division 4 parts (PMAT)
Results in 2 identical nuclei
4 parts (PMAT)
Prophase
Metaphase
Anaphase
Telophase

7. Prophase (Prologue) DNA organizes into X-shaped chromosomes
Chromosomes are made of 2 identical sides called sister chromatids
Nucleolus disappears
Nuclear membrane disappears
Centrioles begin to move to pole of the cell
Spindle begins to form
Spindle is made of microtubules

8. Metaphase (Middle)
Spindles attach to centromere of the chromosome and pull chromosomes into the middle (equator) of the cell
Very important because it ensures that, when the chromosomes split, exactly ½ of each chromosomes (1 sister chromatid) will move to each end of the cell
When the cell splits, it will then have exactly the same DNA as the parent cell (the one that split into the 2 new ones)

9. Anaphase (Apart) Spindle fibers shorten
Sister chromatids are pulled apart at the centromere
One sister chromatid moves to each pole (end) of the cell

10. Telophase (Two) Spindle breaks down DNA uncoils
A nucleus forms around each of the 2 sets of DNA
One forms on each side of the cell
This results in 2 identical nuclei
The cell begins to split

11. Cytokinesis Occurs immediately after mitosis Cyto=Cell
Kinesis=movement
The cytoplasm splits
Results in 2 identical cells
Called the daughter cells
Happens differently in plant and animal cells
In animals, the cytoplasm pinches in until it splits
In plants, this cannot happen due to the cell wall
Instead, a structure called a cell plate forms, splitting the cells
After cytokinesis, cells are back in G1 and the cycle is ready to repeat.

15. Results of Cell Division
Cytokinesis results in 2 new, identical cells
Some unicellular organisms use a similar method as their reproduction
Called binary fission, the parent cell splits into 2 daughter cells, each being an organism
Multicellular organisms use cell division to make new cells for several reasons
Growth
As you grow, you must add new cells
Zygote splits into 2, which split into 4, which split into 8…etc.
Repair
Damage to the body kills cells
They need to be replaced
This could be a scrape, a cut, a broken bone, etc.
Replacement
You lose thousands of cells a day, and they need to be replaced with new ones

16. Not in your Book! Why is it important to understand the cell cycle?
Good to know how you get your cells…
More important is what happens when the cell cycle goes wrong
The cell cycle results in the production of new cells
It regulates when cells are formed and makes sure that there are no issues
However, sometimes DNA can be damaged and the cell begins to divide out of control
Leads to a mass of cells in an area
Called a tumor
The cells in the tumor crowd out and steal nutrients from healthy cells
Sometimes they are also able to break free and move throughout the body
This results in one of the most deadly diseases…
Cancer
Can be defined as uncontrolled cell division

20. Levels of Organization
AtomsMolecules
MoleculesOrganelles
OrganellesCells
CellsTissues
TissuesOrgans
OrgansOrgan systems
Organ systemsOrganisms

21. Prokaryotes vs. Eukaryotes
Prokaryotes and some unicellular eukaryotes only get to the cell level
Some eukaryotes, such as sponges, only get to the tissue level
Others have organs, but not organ systems

22. Cell differentiation
The process by which cells become different kinds of cells, doing a specific job
All cells in an organism have identical DNA
However, different cells need different DNA instructions to do their job
Different genes turn on in different cells to make them different
A gene is a segment of DNA that contains instructions
Stem cells are unspecialized cells that are able to become many different types of cells
Many are present in embryos, and are able to become any number of cells for the developing organism
Harvested stem cells may have huge potential for treatment of a number of diseases