1. Prokaryotic Cells IB Topic 2.2

2. Identifying Cells Cells are divided into groups based on major characteristics Cells are divided into two major groups: –Prokaryotic cells –Eukaryotic cells

3. Prokaryotic Cells Much smaller and simpler than eukaryotic cells –Less than 1 μm in diameter Thought to have appeared on Earth first Bacteria are prokaryotic cells –Fun fact: The word “pro” means before The word “karyon” means kernel (referring to the nucleus) Both are Greek

4. Features of Prokaryotic Cells Cell wall Plasma membrane Flagella Ribosomes Nucleoid See Figure 2.1 (page 22)

5. The Cell Wall Cell wall –Protects and maintains the shape of the cell –Composed of carbohydrate-protein complex called peptidoglycan –Some bacteria have an extra layer (polysaccharide) outside the cell wall Allows bacteria to stick to teeth, skin, and food

6. The Plasma Membrane Just inside the cell wall Controls the movement of materials in and out of the cell Plays a role in binary fission Cytoplasm occupies the complete interior of the cell –Jelly-like material –All cellular processes take place in the cytoplasm

7. Fun Fact Some bacteria, like the ones that cause pneumonia and meningitis have a thick outer layer called a capsule –Made of sugars Increases chance of survival Decreases chance of immune system destroying them

8. Pili and Flagella Pili –Hair-like growths outside the cell wall –Used for attachment –Main function: joining bacteria cells to transfer DNA from one cell to another Flagella (or flagellum) –Longer than pili –Allow for mobility

9. Ribosomes Site of protein synthesis Very small structures Appear in very large numbers in cells with high protein production

10. The nucleoid region Non-compartmentalized Contains a single, long, continuous, circular thread of DNA This region is involved in: –Cell control and reproduction Also contain plasmids: –Small, circular DNA –Not connected to the main bacterial chromosome –Replicate independently –Not required by the cell May help the cell adapt to unusual circumstances

11. How do prokaryotic cells divide? Binary Fission Simple process: –DNA is copied –The two daughter chromosomes become attached to different regions on the plasma membrane –The cell splits (divides) into two genetically identical daughter cells –In some bacterial cells, this takes ~20 minutes Huge populations.. Greater potential for infection

12. In conclusion: DNA is not enclosed within a membrane and is one circular chromosome Their DNA is free, not attached to proteins They lack membrane-bound organelles –But do have ribosomes Cell wall is made up of peptidoglycan Divide by binary fission Small in size (1-10 μm)