Regulating the Cell Cycle. Lesson Overview THINK ABOUT IT. How do cells know when to divide? Review: Why do cells divide?

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1 THINK ABOUT IT How do cells know when to divide? Review: Why do cells divide?

2 Controls on Cell Division How is the cell cycle regulated? The cell cycle is controlled by regulatory proteins both inside and outside the cell.

3 The controls on cell growth and division can be turned on and off. For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows when the healing process nears completion.

4 The Discovery of Cyclins Cyclins are a family of proteins that regulate the timing of the cell cycle in eukaryotic cells. Cyclins can be found in the cytoplasm of cells. Levels are highest right before and during mitosis. How was this determined??

5 By an Experiment! A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G 2 of interphase. As a result, the second cell enters mitosis.

6 Regulatory Proteins (different types of cyclins) Internal regulators are proteins that respond to events inside a cell. They allow the cell cycle to proceed only once certain processes have happened inside the cell Checkpoints!! Examples: 1. A cell cannot enter mitosis until its chromosomes have replicated. 2. Cell cannot enter anaphase until spindle fibers are attached. 3. p53 gene detects damaged DNA and halts the cell cycle for repairs.

7 External regulators are proteins that respond to events outside the cell. They direct cells to speed up or slow down the cell cycle. 1. Growth factors are external regulators that stimulate the growth and division of cells. Where would these be important? During embryonic development and wound healing 2. Others have opposite effect halt or slow down cycle Usually present on the cell surface.

8 This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

9 Apoptosis Apoptosis is a process of programmed cell death. Questions to consider Is apoptosis a sign of disease? Apoptosis plays a role in development by shaping the structure of tissues and organs in plants and animals. A controlled process. For example, the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development. Too little apoptosis can result in disease. Too much apoptosis can also result in disease. AIDS and Parkinson s disease are both examples of disease where too much apoptosis has occurred.

10 Cancer: Uncontrolled Cell Growth How do cancer cells differ from other cells? Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, the cells divide uncontrollably.

11 Cancer is a disorder in which body cells lose the ability to control cell growth. Cancer cells divide uncontrollably to form a mass of cells called a tumor. Benign vs. Malignant Tumors: What is the difference?

12 A benign tumor is noncancerous. It does not spread to surrounding healthy tissue. A malignant tumor is cancerous. Invades and destroys surrounding healthy tissue & can spread to other parts of the body. Spread of cancer cells is called metastasis. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning. See Figure p.289 Art in Motion

13 Comparing Normal Cell Division to Cancer Cell Division

14 What Causes Cancer? Cancers are caused by defects in genes that regulate cell growth and division. Some sources of gene defects are tobacco use, radiation exposure, defective genes, and viral infection. A damaged or defective p53 gene is common in cancer cells. Cells unable to respond to growth signals Under normal operating conditions, the p53 gene acts a tumor suppressor (prevents tumors from forming).

15 Treatments for Cancer Some localized tumors can be removed by surgery. Many tumors can be treated with targeted radiation. Chemotherapy is the use of compounds that kill or slow the growth of cancer cells. When or how might these treatments pose a threat to the individual?