The Cell Cycle and Cancer Glencoe Biology Chapter

What causes cancer? Cancer is caused by mutations, which creates abnormal cell growth. A mutation is a change to an organism’s genetic material. In our case, DNA.

What causes mutations? (changes our DNA?) Radiation UV radiation X rays Chemicals Alcohol Tobacco Drugs Infectious agents Viruses like HPV

Genetic Material During most of the cell’s life, genetic material exists in chromatin Chromatin = DNA that is long and tangled Chromatin coils up (during M phase) to form chromosomes When UNCOILED, chromatin can start the process of making proteins and can replicate itself When COILED, cell division can occur

Anatomy of a Chromosome

0.5 µm Chromosome duplication (including DNA synthesis) Centromere Sister chromatids Separation of sister chromatids Centromeres Sister chromatids

The Cell Cycle: The “lifetime” of a cell What do cells spend their lifetime doing? Cells go through THREE (3) periods One of growth and synthesis of DNA One in which the nucleus divides One in which the cytoplasm divides

The Cell Cycle The growth period is called INTERPHASE The stage during which the cell carries out cellular functions Also the stage in which it grows and replicates its DNA. INTERPHASE S (DNA synthesis) G1 Mitosis G2 Cytokinesis MITOTIC (M) PHASE

The Cell Cycle The nuclear division period is called M PHASE (Mitosis) the stage of the cell cycle during which the cell’s nucleus and genetic material divide. Consists of Prophase, Metaphase, Anaphase, and Telophase (PMAT) INTERPHASE S (DNA synthesis) G1 Mitosis G2 Cytokinesis MITOTIC (M) PHASE

The Cell Cycle The cytoplasmic division period is called CYTOKINESIS The method by which a cell’s cytoplasm divides, creating a new cell. INTERPHASE S (DNA synthesis) G1 Mitosis G2 Cytokinesis MITOTIC (M) PHASE

So what does this have to do with cancer? The cell cycle has 3 main checkpoints If a cell receives a go-ahead signal at the G1 checkpoint, it will continue dividing If the cell does not receive the go-ahead signal, it will exit the cycle and not divide Tumors form due to out of control cell division G1 checkpoint Control system S G1 M G2 M checkpoint G2 checkpoint

Mitosis Nucleus Chromatin condensing 10 µm Nucleolus Chromosomes Cell plate Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is starting to form. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelope will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro- tubules shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.

Why do cells need to divide? In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for: Development from a fertilized cell Growth Repair

LE 12-6ca G2 OF INTERPHASE PROPHASE PROMETAPHASE

LE 12-6da 10 µm METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

1st stage of Mitosis: Prophase During Prophase… Chromatin coils up into visible chromosomes The nucleus will disappear during this phase Centrioles will begin to separate

2nd Stage of Mitosis: Metaphase During Metaphase… Spindle fibers pull the chromosomes to the middle (equator/metaphase plate) of the cell

3rd stage of Mitosis: Anaphase During Anaphase… Chromosomes will be pulled apart forming chromatids. Once the chromatids are separated, they will move towards opposite sides of the cell.

4th stage of Mitosis: Telophase During Telophase… The chromatids uncoil, becoming chromatin The nuclear envelope reforms Mitosis is COMPLETE!!!

Cytokinesis: last stage in the cell cycle The cytoplasm (and its contents) will divide into two new cells. ANIMAL CELLS: The cell membrane will move inward and pinch apart PLANT CELLS: A new cell wall forms between the two new cells.