© SSER Ltd. Cell Cycle and Cancer

Objectives Know the stages of the cell cycle. Be able to describe the main processes occurring during each stage of the cell cycle. List some factors that increase the risk of cancer. Describe what cancer is and how it relates to the cell cycle.

The stages through which a cell passes from one cell division to the next constitute the cell cycle The cell cycle is divided into two major phases: the M phase or mitotic phase and the interphase The Cell Cycle

Interphase is divided into G 1, S and G 2 phases G1G1 G2G2 S INTERPHASE MITOSIS (M PHASE) The Cell Cycle Cell division phase

M During interphase, preparations for mitosis take place G 2 - Second Growth Phase The cell grows and prepares for mitosis G 1 - First Growth Phase The cell grows and new organelles and proteins are manufactured S DNA replication takes place The Cell Cycle Nuclear Division Cell division

G1G1 G2G2 S M G 1 is the most variable of all the phases The rapidly dividing epithelial cells lining the human intestine remain in the G 1 phase for only about 2 hours Slowly dividing liver cells may take many months to move through G 1 to the S phase Some cells, such as nerve and muscle cells never divide; they may be considered to be permanently in the G1 phase and never enter the S phase Variations in the Cell Cycle

To do:- Figure 2 Page 170 : Copy Graph showing how mass of DNA changes during the cell cycle (lower graph) and add labels to show which stage of the cell cycle is on each part of the graph.

Photomicrograph showing cells from an onion root tip Note that many of the cells are in interphase

The different phases of the cell cycle last for different periods of time An onion root slide was examined for the different stages of the cell cycle and the number of cells in each phase was recorded Stage of Cell Cycle Number of Cells Cell % (approx) Interphase13866 Prophase5627 Metaphase63 Anaphase21 Telophase73 Total The percentage of cells in each stage was then calculated The percentage of cells in each stage is used as a measure of the percentage of time that the cells spend in each phase of the cell cycle Interphase is the longest stage of the cell cycle with anaphase being the shortest The Timing of the Cell Cycle If cell cycle takes 72 hours to complete, how long is Telophase? 3/100 * 72 = 2.16h

What have these people in common?

The multiplication of cells is a closely regulated process Cell division is under genetic control, and it is known that there are specific genes which code for proteins that ‘switch on’ and ‘switch off’ the process Cancer is a disease that results from uncontrolled cell divisions Normal cells become transformed into cancer cells when the genes that control cell division mutate and become ONCOGENES Environmental cancer-causing agents, known as carcinogens, play a part in causing the alteration of DNA structure that leads to oncogene formation Known carcinogens include ultraviolet radiation, cigarette smoke and X-rays Cancer: The Cell Cycle Out of Control

Scanning Electron Micrograph of Dividing Cancer Cells

When a normal body cell mutates it may divide to produce a clone of cells that form a tumour normal body cell mutated body cell tumour mitosis mutation Many such tumours are found to be BENIGN and do not spread from their site of origin – they may nevertheless compress and damage adjacent tissues Malignant, cancerous tumours may spread from their site of origin These tumours develop their own blood and lymph supply which can transport malignant cells from the tumour to other sites in the body malignant tumour malignant cancer cells carried to other body sites secondary tumour This is called metastasis these cells invade other body regions to form secondary cancers Cancer: The Cell Cycle Out of Control Animations

Uncontrolled cell proliferation causes tumor growth. The cells can detach (metastasise) and move to other organs via the blood stream. Skin Mouth Throat

To Do & complete Answer summary question 1 page 171. Exam style question 2 on p 174 If time: Q 2 on page 171. Homework:- Answer the application questions (greenish box) on page 171. Great link to cancer info