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. there are 2 main phases in a cell cycle interphase periods of growth in the life of a cell; consists of 2 growth stages (more organelles, cell grows larger or else it would be smaller and smaller), and a DNA replication stage (aka synthesis; forms sister chromatids) cell division mitosis and cytokinesis Interphase – periods of growth in the life of a cell; consists of two growth stages and a stage of DNA replication Copyright © 2010 McGraw-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 cell cycle checkpoint is a point in the cell cycle when proteins determine whether cell division should or should not occur there are 3 main points when a cell checks itself: before DNA replication—does cell have enough nutrients to support growth before mitosis—has the DNA replicated before cytokinesis—has mitosis occurred correctly; are there normal amounts of chromosomes in the nuclei very important—many cells leave the cycle at this point, as often, more cells of that type aren’t needed (body doesn’t need cell to divide—they enter a non-dividing stage; most cells in human body are at this stage) when cells leave cycle, they become non dividing—carries out its functions until death they can leave cycle in order to die also cell division won’t occur if: there aren’t enough nutrients to support cell growth DNA hasn’t replicated DNA is damaged Copyright © 2010 McGraw-Hill Ryerson Ltd.

Cell Death and Suicide Cells “die” when they are damaged due to: (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 “pre-programmed 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 McGraw-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 cancer is when cells with abnormal genetic material divide uncontrollably and can spread to other body parts 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) a tumour is an abnormal clump/group of cells the abnormal cells, with further mutation, can become cancer cancer is cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts and continue dividing uncontrollably there cancer can be spread through the body by blood, and continue dividing there normal cells can undergo 20-30 rounds of cell division—any more may result in mutated cells after 20-30 rounds, the cell commits suicide in cancer cells, enzymes cause cells to be unaware of the need to commit suicide or make it impossible to commit suicide most cells stop dividing when they realize they’re not attached to surface; cancer cell doesn’t do that carcinogens are mutagens which cause cancer asbestos, tobacco smoke etc. abnormal cells take up space from normal cells (they take nutrients away from normal cells) tumours reduce effectiveness of other cells’ cancer cells usually have several mutations before control of cell division is lost Copyright © 2010 McGraw-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). cancer is when cells with abnormal genetic material divide uncontrollably and can spread to other body parts 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) a tumour is an abnormal clump/group of cells the abnormal cells, with further mutation, can become cancer cancer is cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts and continue dividing uncontrollably there cancer can be spread through the body by blood, and continue dividing there normal cells can undergo 20-30 rounds of cell division—any more may result in mutated cells after 20-30 rounds, the cell commits suicide in cancer cells, enzymes cause cells to be unaware of the need to commit suicide or make it impossible to commit suicide most cells stop dividing when they realize they’re not attached to surface; cancer cell doesn’t do that carcinogens are mutagens which cause cancer asbestos, tobacco smoke etc. abnormal cells take up space from normal cells (they take nutrients away from normal cells) tumours reduce effectiveness of other cells’ cancer cells usually have several mutations before control of cell division is lost Copyright © 2010 McGraw-Hill Ryerson Ltd.

Answer Review Questions. Task Answer Review Questions.

Concepts to be reviewed: 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 McGraw-Hill Ryerson Ltd.