1 4 THE CELL CYCLE Learning Objectives To

1. 4 THE CELL CYCLE Learning Objectives: To learn the cell cycle and to understand how cancer is related to it. Keywords: Interphase Cell cycle Cell Cycle Checkpoint Tumour Cancer

LIFESPAN OF CELLS The lifespan of different cells varies – some cells live a rough life (exposed to constant abrasion and toxins) meaning they need to be replaced more – Stomach (2 days) and skin cells (20 days) are replaced the most frequently Some cells are encouraged to divide, while others are encouraged to “stay as they are”

1. 4 The Cell Cycle (Page 40) Cells within the human body have finite life spans. The cell cycle controls the production (through interphase, mitosis, and cytokinesis) of new cells of a variety of different types. Interphase – periods of growth in the life of a cell; consists of two growth stages and a stage of DNA replication Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.

Cell Cycle Checkpoints (Page 41) Cell Cycle Checkpoints – a point in the life of a cell when proteins determine whether cell division should or should not occur Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.

Cell Death and Suicide (Page 42) Cells “die” when they are damaged due to: • exposure to toxic chemicals or conditions • physical forces • the wear and tear of daily use Cell “suicide” occurs when the cell experiences a “preprogrammed death” due to: • “suicide” genes code for proteins that kill the cells in specific situations. • cell contents are packaged for use by other cells Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.

Cancer and the Cell Cycle (Pages 43 -44) Tumour – an abnormal clump of cells formed when cells divide repeatedly and excessively Cancer – cells with abnormal genetic material that are dividing uncontrollably and can spread to other parts of the body Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.

Cancer and the Cell Cycle (Pages 43 -44) Some cells are transformed so that they ignore the checkpoints in the cell cycle. Instead of leaving cycle to die, they divide repeatedly and excessively, forming a clump of cells (tumour). Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.

TASK Answer Review Questions.

Section 1. 4 Review (Page 45) Concepts to be reviewed: • the stages of the cell cycle • the function of cell cycle checkpoints • cell death and cell suicide • cancer and how it is related to the cell cycle Copyright © 2010 Mc. Graw-Hill Ryerson Ltd.