Mitosis and the Cell Cycle Cell reproduction

Some Definitions Somatic Cells – body cells Produced through mitosis Has 46 chromosomes (23 pairs) Homolog – each member of a chromosome pair Diploid (2n) – total of 46 chromosomes in people – zygote & somatic cells Haploid (n) – total of 23 chromosomes in people, gametes (sperm & egg)

The Cell Cycle The sequence of growth and division of a cell. 95% of cell cycle in interphase 5% of cell cycle in mitosis

Cell Cycle 4 phases of the cell cycle G1 Phase includes a G0 S Phase M Phase (Mitosis and Cytokinesis happens during this phase)

Interphase Growth Stage 1 (G1) – metabolic activity of the cell G0 is a resting phase Synthesis Stage (S) – metabolic activity of the cell, replication of DNA Growth Stage 2 (G2) – metabolic activity of the cell, prepare for division

Checkpoint control system Checkpoints cell cycle controlled by STOP & GO chemical signals at critical points signals indicate if key cellular processes have been completed correctly

Cancer and the Cell Cycle Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell’s DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor.

Frequency of cell division Frequency of cell division varies by cell type embryo cell cycle < 20 minute skin cells divide frequently throughout life 12-24 hours cycle liver cells retain ability to divide, but keep it in reserve divide once every year or two mature nerve cells & muscle cells do not divide at all after maturity permanently in G0

Anatomy of a Chromosome Sister chromatids One original and one copy from the S phase Centromere Center where sister chromatids attach

Mitosis Happens in all cells except sex cells (gametes) which is a different process. Nuclear Division (division of the nucleus) 4 major stages

1st Stage - Prophase Nuclear envelope disappears Chromosomes condense – can see sister chromatids and centromere Spindle forms Centrioles go to poles

2nd Stage - Metaphase Chromosomes move to the equator of spindle Each chromatid is attached to spindle with centromere

3rd Stage - Anaphase Centromeres split Sister chromatids are pulled apart to opposite poles of the cell Each chromatid is now a separate chromosome

4th Stage - Telophase Nuclear envelopes (2) reform Chromosomes begin to uncoil Cleavage furrow forms

After Telophase Mitosis is complete; cell division is not!!! NOTE: After Telophase Mitosis is complete; cell division is not!!!

Cytokinesis Division of the Cytoplasm Two new daughter cells are now separate (both identical to the original parent cell) When cytokinesis is complete; cell division is complete.