Journal: What is mitosis? Why is it important? January 19, 2017 Journal: What is mitosis? Why is it important? Hand in your homework

The Cell Cycle

The Cell Cycle Four Phases G1 – Gap 1 S – DNA Replication G2 – Gap 2 Mitosis

Interphase Occurs when the cell is not dividing Cells spend the majority of their time in this phase Made up of three phases G1 – Growth Phase S – DNA Replication Occurs G2 – Growth Phase

Mitosis Division of the nucleus Occurs in 4 stages: PMAT Prophase Metaphase Anaphase Telophase http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf

1st: Prophase The nuclear membrane disappears

2nd: Metaphase Pairs of chromosomes line up at the center of the cell

3rd: Anaphase Pairs of chromosomes separate and begin to move to opposite ends of the cell

4th: Telophase Two new nuclei form around the chromosomes Chromosomes become chromatin (threads rather than X’s) Mitosis ends

Cytokinesis Last stage of the cell cycle Not part of mitosis Cell membrane pinches inwards to create two daughter cells – each with its own nucleus with identical chromosomes

How long does the cell cycle take?

How is the cell cycle regulated? Cyclins – proteins that regulate the amount of time spent at each stage of the cell cycle

Checkpoints At the end of each stage cells must pass through checkpoints to make sure that the cell is at the appropriate point in the cell cycle If not, the cell will be destroyed When cells that should not pass through the checkpoint do anyway it results in cancer

What is cancer? Cancer is the uncontrolled cell growth of abnormal cells in the body.

How does cancer occur? Step 1: External factors cause mutations in the DNA Can be genetic or caused by carcinogens (cancer causing agents) Step 2: Cell loses its ability to control it’s grow and division Step 3: Over an extended period of time, a mass of cells known as a tumor will form

Formation of Tumors

Types of Tumors Slow growing and does not metastasize Malignant Tumors Fast growing Likely to metastasize (spread to other parts of the body and cause problems) Benign Tumors Slow growing and does not metastasize