1. Recap on Cell Size
cells are limited in their size because of 3 things:
1. Diffusion
2. DNA
3. Food Requirements
Therefore, Cells have 2 methods of dealing with cell size:
Altered Shape
Cell Division
We are going to learn how cells Divide!

2. Cell Theory & Chromosomes
Recall that Cell theory states “all cells come from preexisting cells.”
Cell Division results in two cells that are identical to the original, parent cell
Chromosomes – “colored bodies” that contain genetic material.
It is the identity of the cell
Accurate transmission of chromosomes during cell division is critical.

3. The Cell Cycle Cell Cycle – sequence of growth and division of a cell
Broken into 2 Parts:
Interphase : Growth
Mitosis : Division
A cell spends most of its life in INTERPHASE
Cell division is during mitosis
One final process, division of the cytoplasm, cytokinesis, takes place after mitosis.

4. Cell Cycle - Interphase
During Interphase…
Cell grows in size
Carries on metabolism
Replicates chromosomes
Composed of 3 Phases:
G1 : Chromosomes are not yet visible, rapid protein synthesis due to growth
S : Chromosomes are replicated in the nucleus (sister chromatids)
G2 : Chromosomes shorten & coil, protein synthesis prepares for Mitosis, centrioles prepare to make the mitotic spindle, cell organelles are replicated

5. Cell Cycle: Mitosis - Prophase
There are 4 Stages of Mitosis
1.) PROPHASE
First and longest stage
Chromatin coils up into visible chromosomes
Sister Chromatids are visible (2 exact copies of DNA for the 2 new cells) from interphase
Sister Chromatids are held together by a centromere
Nucleus begins to disappear
Nucleolus disintegrates
Animal Cells – Centrioles Migrate to the poles for chromatin separation
Spindle forms – for sister chromatid separation. In Plant cells the spindle forms without centrioles.

6. Chromatin – long strands of DNA wrapped around proteins, it only becomes chromosomes for replication and protein synthesis.
Centromere – Structure that holds sister chromatids together. Plays a role in chromosome movement during mitosis. By their characteristic location, centromeres also help scientists identify and study chromosomes.

7. Cell Cycle: Mitosis - Metaphase
During Metaphase…
Short second phase
Doubled chromosomes become attached to the spindle fibers by their centromeres
Chromosomes are pulled by the spindle fibers
Begin to line up on the midline or equator of the spindle
Each sister chromatid is attached to its own spindle fiber
One spindle fiber extends to one pole, the other to the opposite pole
Ensures that each new cell receives an identical and complete set of chromosomes.

8. Cell Cycle: Mitosis - Anaphase
During Anaphase…
Third phase of mitosis
Separation of sister chromatids at the beginning
Centromeres split apart
Chromatid pairs from each chromosomes separate from each other
Chromatids are pulled apart by the shortening of the microtubles in the spindle fibers

9. Cell Cycle: Mitosis - Telophase
In Telophase…
The fourth and final stage
Begins as chromatids reach the opposite poles of the cell
Many of the Mitotic changes that took place are reversing for the two new cells
Chromosomes unwind for protein synthesis
Spindle breaks down
Nucleolus reappears
New nuclear envelope forms around each set of chromosomes
A new double membrane begins to form around the 2 new nuclei

10. Mitosis - Cytokinesis
Following telophase, the cell’s cytoplasm divides in a process called Cytokinesis
In Animal Cells – plasma membrane pinches in along the equator
In Plant Cells – a cell plate is laid down across the cell’s equator. A cell membrane forms around each cell, and new cell walls form on each side of the cell plate until separation is complete.

11. Your Turn!
Place the following images in order of Mitosis with numbers, and give the name of the cycle. Let interphase be step 5.

12. How did you do? 2 - Metaphase 1 - Prophase 4 - Telophase 3 - Anaphase
5 - Interphase

13. Results of Mitosis Mitosis gives genetic continuity
Daughter cells will carry out the same process or job as the parent cell
Results in groups of cells
Atoms form Molecules
Molecules form Cells
Cells form Tissues
Tissues form Organs
Organs form Organ systems
Organ Systems form an Organism
Remember! The Cell is STILL the most basic unit of organization.