1. KEY CONCEPT Cells divide during mitosis and cytokinesis.

2. Chromosomes condense at the start of mitosis.
DNA is a double-stranded molecule, like a twisted ladder.
DNA is made of four subunits called nucleotides.
Nucleotides are made of three parts: a sugar, a phosphate group and a base.
DNA double helix
DNA and histones
Chromatin
Supercoiled DNA

3. Chromosomes condense at the start of mitosis.
A chromosome is one long strand of DNA.
Each of our body cells has 46 chromosomes.
DNA in each chromosome has multiple genes.
DNA in ONE cell would stretch out to be 10 feet long.
HOW ON EARTH does it fit in the cell?
DNA wraps around proteins called histones that condense it.
DNA wraps around these histones, similar to beads on a string.
DNA is loose like spaghetti, which describes how it folds back on itself, not that it is loosely wrapped around the histones.
This loose DNA is called a chromatin. Let’s look.

4. DNA plus histones (proteins) is called chromatin.
One half of a duplicated chromosome is a chromatid.
The two identical chromatids are called sister chromatids.
Sister chromatids are held together at the centromere, the area that appears to be pinched.
Telomeres are the ends of the chromatids that are made of repeating nucleotides.
They protect DNA and do not include genes.
A small section of the telomeres are lost when DNA is copied.
chromatid
telomere
centromere
Condensed, duplicated chromosome

5. Interphase prepares the cell to divide.
Mitosis and cytokinesis produce two genetically identical daughter cells.
Parent cell
centrioles
spindle fibers
centrosome
nucleus with
DNA
Interphase (#1 on PN)
Interphase prepares the cell to divide.
DNA is loosely organized and duplicated
The cell grows to prepare for division
Organelles are duplicated.

6. Interphase Plant Cell Animal Cell
Photographs from:

7. Mitosis occurs in four phases.
Mitosis divides the cell’s nucleus into two genetically identical nuclei, each having its own set of DNA.
Mitosis occurs in ALL bodily cells except those that form eggs or sperm (sex cells).
Mitosis occurs in four phases.
1. Prophase (#2 on PN)
chromatins condense into tight chromosomes
Spindle fibers form.
Nuclear envelope breaks down
Nucleolus disappears
Centrosomes and centrioles migrate to opposite sides of the cell
Spindle fibers grow from the centrioles and radiate towards the cell center

8. Prophase Plant Cell Animal Cell
Photographs from:

9. Mitosis divides the cell’s nucleus in four phases.
2. Metaphase (#3 on PN)
Spindle fibers attach to a protein structure on centromere of each chromosome
Chromosomes then line up in the middle of the cell.

10. Metaphase Plant Cell Animal Cell
Photographs from:

11. Mitosis divides the cell’s nucleus in four phases.
3. Anaphase (#4 on PN)
sister chromatids separate from each other
Spindle fibers shorten
This pulls the sister chromatids away from each other to opposite sides of the cell.

12. Anaphase Plant Cell Animal Cell
Photographs from:

13. Mitosis divides the cell’s nucleus in four phases.
4. Telophase (#5 on PN)
Complete set of identical chromosomes is positioned at each pole of the cell
They begin to form the new nuclei and chromosomes begin to uncoil.
Nuclear membrane starts forming
Spindle fibers fall apart

14. Telophase Plant Cell Animal Cell
Photographs from:

15. Cytokinesis (#6 on PN)
divides the cytoplasm between the two daughter cells and completes the cell cycle.
It differs in animal and plant cells.
In animal cells, the membrane pinches closed.
In plant cells, a cell plate forms.

16. Single celled organisms use cell division to reproduce
Multicellular organisms use cell division for growth, development and repair

17. Mitosis Animation