The Cell Cycle Mitosis & Cytokinesis

Why do living things grow? This baby king penguin grows because he produces more and more cells.

How do cells know when to quit dividing? Cell growth is CAREFULLY controlled. Only certain cells are allowed to divide rapidly. Ex. Hair follicles & stomach lining.

One experiment using cells in a petri dish showed that they stopped dividing when they touched! But……

That’s not always the case… Breast cancer cell Liver Cancer cells

Mitosis The process where the nucleus divides into two new, IDENTICAL, nuclei.

During the early stages of Mitosis… The chromatin (DNA + Proteins) becomes condensed (gets tighter) and you can see the chromosomes.

Chromosomes Chromosomes are tightly coiled chromatin/DNA.

A Chromosome *Two sister CHROMATIDS Make up the chromosome *The CENTROMERE, a sticky Spot in the middle of the Chromosome, keeps the sister Chromatids together.

Interphase A long period between cell divisions. Doubling of all cell parts happens. Most cells, when looked at under the microscope are in interphase because it takes the longest time.

M I T O S I S

The process of cell growth & division Mitosis is… The process of cell growth & division .

There are 4 parts of Mitosis: P Prophase M Metaphase A Anaphase T Telophase

Interphase Prophase Anaphase Telophase

Interphase This cell shows how all cells look before mitosis. Interphase is a phase of the cell cycle, but NOT a stage of mitosis.

Prophase The nuclear membrane breaks down. The chromosomes become visible (shorten and thicken). The other structures important for mitosis are also forming (ex. the centrioles).

Metaphase *The chromosomes are pulled to the cell's equator by the spindle fibers. *The chromosomes MEET IN THE MIDDLE

Anaphase The newly formed chromosomes are pulled by the spindle fibers, AWAY from each other, toward opposite poles of the cell.

Telophase The chromosomes stop moving. The spindle fibers break down. The membrane of the cell pinches creating two separate cells. The nuclear membrane reforms. The nucleolus reappears.

Very Last Part… Cytokinesis This is when the two new cells completely divide. Plant and animal cells do this differently!

Animal Cell A ring (contractile ring) tightens and tightens until the two new cells pinch apart. Furrow

Plant Cell A cell plate forms between the two cells and this forms into the cell wall eventually.