Regulating the Cell Cycle 10.3

WARM UP: Label the next blank page in your notebook  10.2 Review Warm Up. Copy and answer the following questions on this page: 1. How does the structure of chromosomes differ in prokaryotes and eukaryotes? 2. During which phase of the cell cycle are chromosomes replicated? 3. What happens during each of the 4 phases of mitosis? Write 1 sentence for each phase. 4. What is cytokinesis and why does it occur? 5. How does cytokinesis differ in animal and plant cells?

Controls on Cell Division: How is the cell cycle regulated?

Discovery of Cyclins: In the early 1980s, biologists discovered a protein in cells that were going through mitosis  cyclin Biologists have since discovered a family of proteins known as cyclins that regulate the timing of the cell cycle in eukaryotic cells

Regulatory Proteins: Since the discovery of cyclins, scientists have discovered dozens of other proteins that also help regular the cell cycle. The cell cycle is controlled by regulatory proteins both inside and outside the cell.

Internal Regulators: Respond to events occurring inside a cell Allow the cell cycle to proceed only when certain events have occurred in the cell itself Example: several regulatory proteins make sure a cell does not enter mitosis until its chromosomes have replicated

External Regulators: Proteins that respond to events outside the cell direct cells to speed up or slow down the cell cycle Growth factors = important group of external regulatory proteins Stimulate the growth and division of cells Important during embryonic development and wound healing Other external regulators cause cells to slow down or stop their cell cycles Prevents excessive cell growth and keeps body tissues from disrupting one another

Apoptosis: As new cells are produced, other cells die. Cells end their life cycle in two possible ways: By accident due to damage or injury May be programmed to die = apoptosis Once apoptosis is triggered… 1. the cell and its chromatin shrink 2. part of the cell’s membranes break off 3. neighboring cells then quickly clean up the cell’s remains

Cancer: Uncontrolled Cell Growth Cancer = a disorder in which body cells lose the ability to control growth Cancer cells do not respond to the signal that regulate the growth of most cells Cancer cells form a mass of cells called a tumor Not all tumors are cancerous Some tumors are benign = noncancerous Do not spread to the surrounding healthy tissue or to other parts of the body Cancerous tumors are malignant  invade and destroy surrounding healthy tissue As cancer cells spread, they absorb the nutrients needed by other cells, block nerve connections, and prevent the organs they invade from functioning properly

What causes cancer? By defects in the genes that regulate cell growth and division Several sources: Smoking/chewing tobacco Radiation exposure Other defective genes Viral infection Some cancer cells will no longer respond to external growth regulators, and some fail to produce the internal regulators that ensure orderly growth.

What causes cancer? (cont.) A lot of cancer cells have a defect in a gene called p53 – normally stops the cell cycle until all chromosomes have been properly replicated damaged or defective p53 genes cause cells to lose the information needed to respond to signals that normally control their cell growth

Treatments for Cancer: 1. Tumor is removed When a cancerous tumor is found, it can often be removed by surgery. Example: skin cancer 2. Radiation Carefully targeted beams of radiation Cancer cells are vulnerable to radiation because they grow rabidly and need to copy their DNA more quickly than most normal cells 3. Chemotherapy Chemical compounds that kill cancer cells Also interferes with cell division in normal, healthy cells Serious side effects in many patients