Mitosis, Cytokinesis, Cell Cycle

I) Why Do Cells Divide?

1) Too Big

a) Too Big to Transport Materials

b) Too Big to Control

1.72 3.52

cm cm

Surface to Volume Math

Surface Area of a Cube = Length x Width x 6

Volume of a Cube = Length x Width x Height

1 cm cube:

Surface Area = 1 cm x 1 cm x 6 = 6 cm2 6

Volume = 1 cm x 1 cm x 1 cm = 1 cm3 1

2 cm cube:

Surface Area = 2 cm x 2 cm x 6 = 24 cm2 24 = 3

Volume = 2 cm x 2 cm x 2 cm = 8 cm3 8 1

I) Why Do Cells Divide?

2) Too Small

a) Surface Area to Volume Ratio Too Small

b) Cell Membrane Too Small to Exchange Materials

II) When Do Cells Divide?

1) Growth – Somatic (body) cells undergo

mitosis for growth.

2) Maintenance – Somatic cells use mitosis

to repair damage.

3) Asexual Reproduction – Mitosis is the

process used by some organisms to

reproduce (budding, etc…)

III) Cell Cycle: I – M & C – I (x 2)

1) Interphase: G1, S, G2

2) G1= Growth of Cell (After Division)

3) S = Synthesis (of DNA) and Continued Growth

4) G2 = Growth and Prepare to Divide

5) M = Mitosis (PMAT)

6) C = Cytokinesis = Division of Cytoplasm

IV) Chromatin vs Chromosomes

1) Both GENETICALLY Identical DNA

2) Same Nucleotide Sequence

3) Chromatin Uncoiled

4) Chromosome Coiled

V) Chromosomes

1) Centromere:

a) Holds Sister Chromatids together

b) Spindle Fibers Attach

2) Sister Chromatids:

a) Half of a Chromosome

b) Contain Alleles

3) Chromosomes (Replication)

a) S phase

b) Chromosomes

Replicated

(Copied)

before

Mitosis

MITOSISDIVI SION

O F

T H E

NUC L EUS

VI) Mitosis: Prophase

1) Prophase: First True Stage of Mitosis

a) DNA coils into Chromosomes

b) Chromosomes are Connected by a Centromere

making One Chromosome with Sister Chromatids

c) Centrioles appear

d) Centrioles move to opposite poles

e) Nuclear Membrane breaks down, releasing

Chromosomes (DNA)

f) Spindle Fibers form (Microtubules) at Centrioles

g) Spindle fibers attach the Centrioles (Anchor) to the

Centromere of the Sister Chromatids (DNA)

VI) Mitosis: Metaphase

2) Metaphase: “Middle” Stage of Mitosis

a) Spindle Fibers attached to the

Centromeres of the Chromatids move

the Chromosomes to the middle

b) Sister Chromatids are aligned in the

Middle of the Cell

VI) Mitosis: Anaphase

Anaphase: Third Stage of Mitosis

a) Spindle Fibers attached to the

Centromeres of the Chromatids

separate the Sister Chromatids

b) Sister Chromatids are pulled to

Opposite ends of the Cell

c) Separated Chromatids are now called

Individual Chromosomes

VI) Mitosis: Telophase

4) Telophase: Reverse of Prophase

a) Spindle Fibers release the Centromeres of

the New Chromosomes

b) The Centrioles and Spindle fibers all

“Disappear”

c) TWO Nuclear Membranes Form surrounding

the Chromosomes at EACH end of the Cell

d) The Chromosomes Uncoil back into strands

of Chromatin (DNA)

VII) Cytokinesis (NOT MITOSIS)

Cytokinesis: Not Mitosis, Division of Cytoplasm

a) Cytoplasm Divides

b) New Cell Membrane is Formed

c) Two New “Daughter” Cells are Formed with:

1) Equal Number of Chromosomes

2) Approximately Equal Cytoplasm and

Organelles

d) Back into Interphase at G1

Summary of Mitosis• Prophase:

• Chromosomes condense• Nuclear envelope disappears• centrosomes move to opposite sides of the cell• Spindle forms and attaches to centromeres on the chromosomes

• Metaphase• Chromosomes lined up on equator of spindle• centrosomes at opposite ends of cell

• Anaphase• Centromeres divide: each 2-chromatid chromosome becomes

two 1-chromatid chromosomes• Chromosomes pulled to opposite poles by the spindle

• Telophase• Chromosomes de-condense• Nuclear envelope reappears• Cytokinesis: the cytoplasm is divided into 2 cells