Topic 2.2 Prokaryotic Cells

1. Topic 2.2 Prokaryotic Cells IB Biology 2010

2. Objectives • 2.2.1-Draw and Label a diagram of the ultrastructure of Escherichia coli as an example of a prokaryote. • 2.2.2 -Annotate the diagram with the functions of each named structure. • 2.2.3-Identify structures from 2.2.1 in electron micrographs of E. coli • 2.2.4-State that prokaryotic cells by binary fissions

3. What is a Prokaryotic Cell? • Cells are often divided into certain groups based on major characteristics • One such groupings divide cells into two groups: prokaryotic and eukaryotic • Prokaryotic cells are much smaller and simpler than eukaryotic cells • Most prokaryotic cells are less than 1 micrometer in diameter

4. Feature of prokaryotic cells • Study Figure and be sure you can identify: • Cell wall • Plasma membrane • Flagella • Ribosomes • Nucleoid

5. Electron micrographs of E. coli

6. Cell Wall • Prokaryotic cell wall protects and the maintains the shape of the cell • Composed of carbohydrate-protein complex called Peptioglycan • Some bacteria have an additional layer of a type of polysaccharide outside the cell wall • This layer makes it possible for some bacteria to adhere to structures such as teeth, skin, and food

7. Plasma membrane • Located just inside the cell wall and has a composition similar to the membrane of eukaryotic cells • Functions-controls the movement of materials in and out of the cell. It also plays a role in binary fission • Cytoplasm—occupies the complete interior of the cell

8. Pili and Flagella • Pili-hair-like growths on the outside of the cell wall • Used for attachment, and in joining bacterial cells in preparation for the transfer of DNA from one cell to another • Flagella-they are longer than the pili and allow cell motility

9. Ribosome • Occur in all prokaryotic cells and they function as sites of protein synthesis • They occur in very large numbers in cells with high protein production • Cause a granular appearance to an electron micrograph

10. The nucleoid region • It is non-compartmentalized • Contains a single, long, continuous, circular thread of DNA • Region is involved with cell control and reproduction • Plasmids-small, circular DNA molecules that are not connected to the main bacterial chromosome • Replicate independently of the chromosomal DNA • Not needed for everyday functions but does help adapt to unusual circumstances

11. Binary Fission • Prokaryotic cells divide by a very simple process called binary fission • During this process, the DNA is copied, the chromosmes become attached to different regions on the plasma membrane, and the cell divides into two genetically identical daughter cells. • This divisional process includes an elongation of the cell and a partitoning of the newly produced DNA by microtubule-like fibers made of protein called FtsZ.

12. Binary Fission

13. Summary • Here is a list of major distinguishing characteristics of prokaryotic cells • Their DNA is not enclosed within a membrane and is one circular chromosome • Their DNA is free; it is not attached to proteins • They lack membrane-bound organelles. Ribosomes are complex structures within the plasma membrane, but they have not exterior membrane • Their cell wall is made up of Peptidoglycan • They usually divide by binary fission • They are characteristically small in size, usually 1-10 µm