1. Mitosis Cell Division
Timothy G. Standish, Ph. D.

2. In The Beginning One
Most of the organisms we see started out as one cell
Humans start out as a single cell, the zygote, formed by uniting a sperm and egg
The zygote divides to make approximately one trillion cells
During the process of dividing, cells become specialized to function in the various tissues and organs of the body
Mitosis is the process of cell division in eukaryotic cells

3. Why Cells Must Divide
In multi-celled organisms (like humans) cells specialize for specific functions thus the original cells must divide to produce different kinds of cells
Cells can only take in nutrients and excrete waste products over the surface of the membrane that surrounds them. The surface to volume ratio decreases with the square of the volume (unless special accommodations are made)
1 cm
Surface 6 cm2/
volume 1cm3= 6
2 cm
Surface 24 cm2/
volume 8 cm3 = 3

4. The Cell Lifecycle
The cell lifecycle is well defined and can be divided into four stages:
Gap 1 (G1) - The growth phase in which most cells are found most of the time
Synthesis (S) - During which new DNA is synthesized
Gap 2 (G2) - The period during which no transcription or translation occurs and final preparations for division are made
Mitosis - Cell division

5. The Cell Life Cycle G1 S G2 M
Gap 1 - Doubling of cell size. Regular cellular activities. transcription and translation etc.
Synthesis of DNA - Regular cell activities cease and a copy of all nuclear DNA is made G1 S G2
Gap 2 - Final preparation for division M
Mitosis - Cell division

6. Stages Of Mitosis
During mitosis an exact copy of the genetic material in the “mother” cell must be distributed to each “daughter” cell
Each stage of mitosis is designed to achieve equal and exact distribution of the genetic material which has been copied during the S phase of the cell cycle

7. Stages Of Mitosis Interphase
Interphase - The in between stage - Originally metaphase was thought to be a resting stage now we know that this is the stage most cells spend their time in doing the things that cells do and, if they are preparing to divide, growing and replicating their DNA
Interphase G1 M G2 S

8. Stages Of Mitosis
Prophase - The beginning phase - DNA which was unraveled and spread all over the nucleus is condensed and packaged
Metaphase - Middle stage - Condensed chromosomes line up along the equator of the cell
Anaphase - One copy of each chromosome moves to each pole of the cell
Telophase - End stage - New nuclear membranes are formed around the chromosomes and cytokinesis (cytoplasm division) occurs resulting in two daughter cells

9. Stages Of Mitosis Mother cell Nucleus with un-condensed chromosomes
Interphase
Nucleus with un-condensed chromosomes
Prophase
Condensed chromosomes
Equator of the cell
Metaphase
Disappearing nuclear membrane
Poles of the cell
Anaphase
Two daughter cells
Mitotic spindle
Telophase

10. Packaging DNA T G A Histone C octomer Histone proteins 2 nm
T A
G C
C G TA T A G C
C G
G C
T A
A T
Packaging DNA
Histone proteins
Histone
octomer
2 nm
B DNA Helix

11. Packaging DNA T G A Histone C G C octomer Histone proteins 2 nmTA
G C
T A
C G
A T
A T
2 nm
C G
B DNA Helix
G C
T A

12. Packaging DNA T G A 11 nm Histone C G C octomer Histone proteinsTA
G C
T A
C G
Nucleosome
A T
A T
2 nm
C G
B DNA Helix
G C
T A

13. Packaging DNA
A T
T A
G C
C G
C G
G C
T A
A T

14. Packaging DNA
A T
T A
G C
C G
C G
G C
T A
A T

15. Packaging DNA “Beads on a string” 11 nm 30 nm Looped Domains 200 nm
A T
T A
G C
C G
C G
G C
T A
A T
30 nm
Looped Domains
200 nm
Tight helical fiber
Protein scaffold

16. Packaging DNA 11 nm 30 nm 200 nm 2 nm 700 nm Metaphase Chromosome
Looped Domains
Nucleosomes
B DNA Helix
Tight helical fiber
700 nm G C A T
Metaphase Chromosome
Protein scaffold

17. Chromosomes, Chromatids and Centromeres
A packaged chromosome
Chromatid
Identical
chromatid
Replication
Anaphase
Chromosome arm
Two identical chromosomes
Centromere
Chromosome arm

18. The
End