2 Background Knowledge Answer the following questions: 1. How many cells do you think your body has?2. Why does your body need to have a lot of cells?Each of us began as a single cell, so one important question is:3. How did that single cell develop into a body with more than a trillion cells?
3 I. The Life of a Cell Most cells in the body are called somatic cells. These cells go through a series of stages called the cell cycle.Most of the cell’s life is spent in interphase, a phase of growth and normal functioning.A portion of its life is spent in cell division.
4 II. Cell DivisionCell division, also called cell reproduction, occurs in humans and other organisms at different times in their life.- Multi-cellular organisms grow by increasing the number of their cells.- Cell division replaces worn out or damaged cells.
5 III. The Cell CyclePeriod in which a cell grows, prepares to divide, and then dividesConsists of 3 main stages:1. interphase – the longest period2. mitosis – nuclear division3. cytokinesis – cytoplasm division
6 III. The Cell Cycle Interphase consists of 3 stages: (Checkpoint) G1 - Cell Grows (Checkpoint)S - Genetic Material replicatesG2 - Cell Grows- prepares for mitosis(Checkpoint)
7 IV. CheckpointsControl of the cell cycle occurs with a series of checkpoints – (cell cycle control system)3 Checkpoints:G1 - Checks for normal growth – decides whether the cell will divide.G2 - Checks for proper DNA synthesisM - Checks for proper attachment in mitosis before cells are pulled apart – triggers the exit from mitosisIf any of these checkpoints fail apoptosis (programmed cell death)
10 V. What can go wrong?At any point in the cycle, the cell could malfunction.If it does not pass a checkpoint, it either dies or goes into a permanent resting state.Cancer – a disease that occurs when the cell cycle is no longer regulated