1. Cell Cycle and Mitosis

2. Why do cells divide? 1. To heal/repair tissue
4. For the reproduction of unicellular organisms (CALLED BINARY FISSION-like in bacteria)
1. To heal/repair tissue
Why do cells divide?
Watch how the cells divide in the following video clip. What do you notice happening?
3. To keep cell sizes small for increased efficiency
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. WOW MOMENT!
Because of this amazing super coiling process, _____6 feet!_____ of DNA can fit into just 1 of your 100 trillion cells!
The DNA in your body is long enough to go to the Moon and back 300 times!!
How so…?
The average distance to the moon is 1.26 trillion feet, and you have about 600 trillion feet of DNA in your body (6 feet x 100 trillion cells), if put end on end, all of your DNA could reach the moon (about 600 trillion feet one way, round trip=300 times!)

10. Key Chromosome Vocabulary
DNA molecules are packaged into .
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

11. 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

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

13. BOYS VS GIRLS
Autosomes are the chromosomes the both males and females have (#s 1-22.)
Sex chromosomes are different in males vs females. Males have an XY and females have an XX.
Since your parents gave one of their sex chromosomes to make you, which parent was responsible for you to be a boy or girl?
Yep! Your Dad! The mother gives an X but the father will give either an X making you a girl or a Y making you a boy.
So….how fair was this when Henry IIX beheaded or divorced his wives when she didn’t bear him a son??

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

15. 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

16. Early Spindle Apparatus
First Cell is in the stage called Interphase and is getting ready to enter Cell Division or “M-Phase” =has two events: mitosis or meiosis (division of the nucleus) and cytokinesis (division of the cytoplasm)
Late Interphase: G2
Prophase
Centromere
Early Spindle Apparatus
Nuclear membrane disappears
Chromosome consisting of two sister chromatids becomes visible

17. Chromosomes “MEET” in the “Middle”
METAPHASE
Chromosomes “MEET” in the “Middle”
Chromosomes line up at an imaginary line between the centrosomes at opposite ends of the cell.
Metaphase
The spindle attaches to the centromeres.

18. ANAPHASE
ana= through
Chromosomes are “pulled through” the cytoplasm to toward the poles.
Like reeling in a fish, the spindle fibers (microtubules) pull the “sister chromatids” apart so each side has a complete set of daughter chromosomes.
Anaphase

19. 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.

20. What’s the end product?
Two identical daughter cells ready to start the cycle again… or not.
Some cells (like your nerve 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?