Mitosis

Unit 5

What is Mitosis?

• Mitosis is the division of the nucleus

• This is how we get new cells from existing cells

Limits to Cell Growth

• There are two reasons cells divide rather than continue to grow:

1. The larger the cell becomes, the more demands the cell places on its DNA

2. Larger cells have more trouble moving enough nutrients and wastes across the cell’s membrane

1. DNA “Overload”

Nucleus

DNACell Demands

This is like a normal cell

1. DNA “Overload”

+Nucleus

DNACell Demands

This is like a stressed out cell that needs to divide

Exchanging MaterialsTOWN LIMIT

(Cell membrane)

This is like a normal cell

Exchanging MaterialsTOWN LIMIT

(Cell membrane)

This is like a stressed out cell that needs to divide

Division of the Cell

• Cells divide before they get too large.

• The process by which cells divide into two “daughter” cells is called cell division.

This is like each new town getting it’s own “genetic library”!

The Cell Cycle• During the cell cycle, a cell grows, prepares

for division, and divides to form 2 daughter cells, each of which begins the cycle again.

• There are 4 phases:1. G1 phase

2. S phase

3. G2 phase

4. M phase

Cell increases in size, synthesizes new

proteins and organelles

Chromosomes are replicated and DNA

synthesis takes place

Usually the shortest phase. Many of the

organelles and molecules required for

cell division are produced

Mitosis is further divided into 4 phases

and cell division occurs at the end

4 Phases of Mitosis

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Prophase• Longest part of Mitosis

(50-60% of the time)

• Chromosomes become visible

• Centrioles near the nuclear envelope move toward opposite poles

• Condensed chromosomes become attached to spindle fibers at their centromeres

• Nucleolus disappears and the nuclear envelope breaks down

Metaphase

• Chromosomes line up across the center of the cell (metaphase plate)

• Microtubules connect the centromeres of each chromosome to the two poles of the spindle

Anaphase

• Centromeres split

• Sister chromatids separate toward spindles on opposite sides of the cell

Telophase• Once distinct chromosomes begin

to disperse into a tangle of dense material

• Nuclear envelope re-forms around each cluster (2) of material

• Spindle breaks apart

• Nucleolus visible in each daughter nucleus

• Mitosis is complete

End of Mitosis. What’s Next?

• What we’ve got:– 2 nuclei with duplicate chromosomes in the

cytoplasm of a single cell

• Final task: – Divide the cytoplasm

What is division of the cytoplasm called?

• The division of the cytoplasm is called cytokinesis

Cytokinesis

• In animal cells the cell membrane draws inward and is pinched off forming two separate cells

• In plants, a cell plate forms between the nuclei, turns into a separating membrane and eventually a cell wall

http://www.youtube.com/watch?v=VlN7K1-9QB0

http://www.youtube.com/watch?v=s4PaOz7eWS8