KEY CONCEPT Cell cycle regulation is necessary for healthy growth.

Objectives Identify internal and external factors that regulate cell division. Explain cancer in terms of the cell cycle.

Vocabulary Growth Factor Broad group of proteins that stimulate cell division. Apoptosis Programmed cell death. Cancer Common name for a class of diseases characterized by uncontrolled cell division. Benign Having no dangerous effect on health, especially referring to an abnormal growth of cells that are not cancerous.

Vocabulary Malignant Cancerous tumor in which cells break away and spread to other parts of the body, causing harm to the organism’s health. Metastasize To spread by transferring a disease-causing agent from the site of the disease to other parts of the body. Carcinogen Substance that produces or promotes the development of cancer.

Internal and external factors regulate cell division. External factors include physical and chemical signals. Growth factors are proteins that stimulate cell division. Most mammal cells form a single layer in a culture dish and stop dividing once they touch other cells.

Two of the most important internal factors are kinases and cyclins. External factors trigger internal factors, which affect the cell cycle.

Apoptosis is programmed cell death. a normal feature of healthy organisms caused by a cell’s production of self-destructive enzymes occurs in development of infants webbed fingers

Cell division is uncontrolled in cancer. Cancer cells form disorganized clumps called tumors. Benign tumors remain clustered and can be removed. Malignant tumors metastasize, or break away, and can form more tumors. cancer cell bloodstream normal cell

Cancer cells do not carry out necessary functions. Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.

Carcinogens are substances known to promote cancer. Standard cancer treatments typically kill both cancerous and healthy cells.

Question/Answer Suppose a child was born whose receptors for growth hormone did not work properly. How do you think this would affect the child’s development? The ability of the child to produce new cells and therefore tissues at the proper rate would be affected, which could affect height and weight, but also developing tissues and organs. HeLa cells are also used to study cell signaling processes. What might be a disadvantage of using cancer cells to study processes occurring in healthy cells? Cancer cells are mutants and may not have exactly the same processes as a healthy cell. This could lead to errors.