The Cell Theory and Common Cell Features

1. Cell Features Section 3.2

2. The Cell Theory The Cell Theory has three parts: 1. All living things are made of one or more cells. 2. Cells are the basic units of structure and function in organisms. 3. All cells arise from existing cells.

3. The Cell Theory, continued Cell Size Small cells function more efficiently than large cells. If a cell’s surface area–to-volume ratio is too low, substances cannot enter and leave the cell well enough to meet the cell’s needs.

4. The Cell Theory, continued Common Cell Features: • outer boundary called the cell membrane • interior substance calledcytoplasm • structural support called thecytoskeleton • genetic material in the form of DNA • cellular structures that make proteins, called ribosomes

5. Prokaryotesare single-celled organisms that lack a nucleus and other internal compartments. They have a cell wall, may have cilia or flagella, and have a single circular molecule of DNA. Bacteriaare prokaryotes Prokaryotes

6. Eukaryotes have: A nucleus which contains the cell’s DNA Other internal compartments called organelles. Animals are eukaryotes Eukaryotic Cells

7. Eukaryotic Cells, continued • The cytoskeleton provides the framework of a cell. • There are three basic kinds of fibers: • Microfilaments: long slender filaments made of the protein actin • Microtubules: hollow tubes made of the protein tubulin. • Intermediate fibers: thick ropes made of protein.

8. The cytoskeleton’s network of protein fibers anchors the cell’s organelles and other components of the cytoplasm. Eukaryotic Cells, continued

9. The Cell Membrane • The cell membraneis a selectively permeable barrier that determines which substances enter and leave the cell. • This is caused by the way phospholipids in the membrane interact with water. • A phospholipidis a lipid made of a phosphate group and two fatty acids.

10. The Cell Membrane, continued Cell membranes are made of a phospholipid bilayer

11. The Cell Membrane, continued