1. The Cell Cycle
Chapter 5.1: The Cell Cycle and Mitosis pp 1

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3. 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

4. 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

5. 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
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6. The Cell Cycle
The life of a cell is divided into 3 stages known as the cell cycle:
Interphase
Mitosis
Cytokinesis 3 1 2
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7. 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

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

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

10. 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
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11. 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.
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12. 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