Cell Division

Outline• Cells Review• What is cell

division?• The Cell Cycle• Interphase• Mitosis• 4 Steps of Mitosis• Results of Mitosis

• Meiosis• 8 Steps of Meiosis• Results of Meiosis• 2 Types of Cell

Division

Cells Review• Cell: smallest part of any

living thing that carries out the functions necessary to support life

• Unicellular organism: living thing made up of 1 cell

• Multicellular organism: living thing made up of many cells

What is cell division?• Cell division: a way to

produce more cells– Usually 1 cell divides to make 2

cells

• Why is cell division important to multicellular organisms?– Its how they grow– Replace cells that have died

• Why is cell division important to unicellular organisms?– Its how they reproduce

Cancer cell dividing

E. Coli cell dividing

The Cell Cycle• Cell cycle: everything

that happens from 1 cell division to the next– 2 parts

1. Interphase

2. Mitosis

Interphase• Interphase: longest

part of the cell cycle– The cell prepares to

divide• It grows in size• It copies its DNA

Mitosis• Mitosis: Part of the cell cycle

when the cell actually divides to form 2 identical cells– Produces normal body cells

• Skin and muscle cells

– The cells produced are identical to each other and to the original cell

Mitosis• Mitosis has 4 steps:

1) Prophase

2) Metaphase

3) Anaphase

4) Telophase

4 Steps of Mitosis

1. Prophase– 1st step– Nucleus disappears– Chromosomes form

in nucleus (look like X’s)• These are how the

DNA is stored in our cells

• Humans have 46 single chromosomes (23 pairs)

4 Steps of Mitosis

2. Metaphase– 2nd step– Chromosomes

are lined up in the middle of the cell

4 Steps of Mitosis

3. Anaphase– 3rd step– Chromosomes

are pulled apart– ½ of each

chromosome goes to each end of the cell

4 Steps of Mitosis

4. Telophase– 4th step– Cytoplasm begins

to pinch in at center of cell

– Eventually the 1 cell splits to form 2 cells• Each new cell has

its own nucleus and set of DNA

Results of Mitosis

• Mitosis produces normal cells in the body– Skin and muscle

cells

• 1 cell splits to form 2 cells– The new cells are

identical to each other

– The new cells are also identical to the original cell

Meiosis• Meiosis: cell division

that produces reproductive cells– Reproductive cells are

also called gametes– 2 basic types of gametes

(reproductive cells)• Females – egg cells• Males – sperm cells

Why Meiosis is Needed

• Fertilization: combining of sperm and egg cells to form a zygote– the zygote then grows and develops into a new

organism– how living things reproduce sexually (combining of 2

cells)

Meiosis

• Meiosis has 8 steps – Basically goes through

mitosis twice– There are 2 cell

divisions

Meiosis• 8 Steps of Meiosis:

– Prophase 1– Metaphase 1– Anaphase 1– Telophase 1– Prophase 2– Metaphase 2– Anaphase 2– Telophase 2

Results of Meiosis• Meiosis produces

reproductive cells (gametes)– Sperm and egg cells

• 1 cell splits to form 4 cells– The 4 new cells have ½ of

the DNA that the original cell had

– Haploid cells: cells with ½ of the amount of DNA of a normal cell

– Diploid cells: cells with the normal amount of DNA

2 Types of Cell Division in Humans

½ the DNAComparison to original cell

Identical

23 (single)# of chromosomes in cells

46 (single)

4# of cells produced2

PMAT (1 and 2)Step namesPMAT

8# of steps4

Reproductive cellsTypes of cells produced

Normal body cells

MeiosisCharacteristicsMitosis

2 Types of Cell Division in Humans