The Cell Cycle Chapter 5.1: The Cell Cycle and Mitosis pp. 150-155 1

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What am I? What am I really??? A: Dust! A: Dead skin cells! Over 70% of the dust in your home is made up of tiny flakes of skin we lose on a daily basis. Each day, you shed millions of skin cells per hour. Each month, you replace the outer layer (the epidermis) of your skin. 3

Introduction to the Cell Cycle Q: Ever wonder how we as humans can grow from a single cell into trillions? How do you think it happens? A: Cells must divide and multiply in number in order to create all of our tissues, organs, organ systems, etc. Cell division allows one cell to become many cells! A single cell (fertilized egg) Billions of cells (single organism) 4

Cell Replacement and Development Cells divide as a human body grows, and as the body replace cells that wear out. Which body cells are replaced most frequently? Cell Type Rate Of Cell Division Reason For Cell Replacement Stomach lining cells Every 2 days Destroyed by stomach acid Intestinal lining cells Every 3 days Destroyed by bacteria or during digestion Skin cells Every 20 days Wear and tear during everyday activities or accidents such as scratches p. 152 5

The Cell Cycle The life of a cell is divided into 3 stages known as the cell cycle: Interphase Mitosis Cytokinesis 3 1 2 p. 153 6

The Cell Cycle interphase: the first and longest stage, in which cells carry out life functions and prepare for cell division mitosis: the second and shortest stage of the cell cycle; the process in which the duplicated contents of the cell’s nucleus divides into two equal parts cytokinesis: the final stage of the cell cycle, which separates the two nuclei and cell contents into two daughter cells 7

Interphase interphase: “inter” = between  between phases Interphase can be divided into 3 parts: Growth and preparation Replication Continued growth and preparation 8

Growth and preparation Cell increases in size. Some organelles begin to duplicate. 9

b) Replication The cell copies the DNA in the nucleus  the cell temporarily has two complete sets of DNA Step 1: Enzyme separates DNA sides Step 3: Two new identical DNA molecules are produced Step 2: New bases pair with original bases on original DNA p. 154 10

c) Continued growth and preparation cell continues to grow and make materials Chromatin (containing the replicated DNA) is in a loosely coiled form  can be copied into RNA  proteins can be made. The rest of the Organelles will be duplicated. p. 155 11

The Cell Cycle interphase: the first and longest stage, in which cells carry out life functions and prepare for cell division mitosis: the second and shortest stage of the cell cycle; the process in which the duplicated contents of the cell’s nucleus divides into two equal parts cytokinesis: the final stage of the cell cycle, which separates the two nuclei and cell contents into two daughter cells 12