1. Cell Cycle and Mitosis

2. Why do cells divide? 1. To heal/repair tissue
Watch how the cells divide in the following video clip. What do you notice happening?
4. For the reproduction of unicellular organisms (like bacteria)
3. To keep cell sizes small for increased efficiency
1. To heal/repair tissue
Why do cells divide?
2. For multicellular organisms to grow in size

3. How many stages of cell division do you see in this image?

5. Cell Cycle The cell cycle is the life cycle of a cell
First, we will look at Interphase… )

6. Interphase Longest stage of cell division (90% of cell cycle)
Nucleus is visible
3 sub-phases:
G1: Cell growth
S: DNA is copied (DNA Replication)
G2: Organelles copied/duplicated to prepare for division. )

7. How do you know these cells are in interphase?
Most of these cells are in Interphase
Intact Nucleus

8. How is DNA packaged into chromosomes?
DNA coils around set of 4 histone proteins, creating a “bead on a string” called a nucleosome
The nucleosome coils into structures called chromatin
Chromatin supercoils = chromosome!

9. Key Vocabulary DNA molecules are packaged into . chromosomes
Human (body cells) have 46
Human (sperm or eggs) have 23
Chromosomes are made of a material called .
chromosomes
somatic cells
chromosomes.
gametes
chromosomes.
chromatin

10. Key Vocabulary Chromatin is composed of and _____
It is supercoiled around proteins, called
Together the DNA and histone molecules form bead-like structures called
proteins
DNA
histones
nucleosome

11. Key Vocabulary The chromosome is duplicated (during S)
Each duplicated chromosome consists of two
These are connected by a .
sister
chromatids
centromere

12. Preparing for Division (G2 of interphase)
Late Interphase: G2
Centrosomes (with centriole pairs)
Nuclear membrane still visible
Nucleolus
Chromatin has been replicated

13. Mitosis (M Phase) Prophase Metaphase Anaphase Telophase
The M Phase consists of:
Mitosis and Cytokinesis
Mitosis: the division of the nucleus
Cytokinesis: the division of the cytoplasm
Four Stages of Mitosis:
Prophase
Metaphase
Anaphase
Telophase

14. Preparing for Division
Late Interphase: G2
Prophase
Centromere
Early Spindle Apparatus
Nuclear membrane disappears
Chromosome consisting of two sister chromatids becomes visible

15. The spindle attaches to the centromeres.
Metaphase
Chromosomes line up at an imaginary line between the centrosomes at opposite ends of the cell.
The spindle attaches to the centromeres.

16. Spindles pull the “daughter” chromosomes appart
Anaphase
Spindles pull the “daughter” chromosomes appart

17. Telophase & Cytokinesis
Two nuclei become visible
In animal cells, a Cleavage Furrow is visible
In plant cells, a cell plate is now visible
Cytokinesis
The cytoplasm and organelles divide.

18. What’s the end product?
Two identical daughter cells ready to start the cycle again… or not.
Some cells (like your nerve and muscle cells) do not undergo division.
For those that do (your skin and the lining of your intestinal tract) how would you know how quickly division takes place?