2.2 Prokaryotic Cells

2.2 Prokaryotic CellsDraw and label a diagram of the

ultrastructure of Escherichia coli (E. Coli) as an example of a prokaryote

Use images of bacteria as seen in electron micrographs to show the structure.

The diagram should show the cell wall, plasma membrane, mesosome, cytoplasm, ribosomes, plasmid, pili, flagella and nucleoid.

2.2 Prokaryotic CellsAnnotate your diagram with the

functions each named structure:cell wall – forms a protective outer

layer that prevents damage from outside and bursting if internal pressure is too high

plasma membrane – controls entry and exit of substances, pumping some of them in by active transport

mesosome – increases the area of membrane for ATP production. May move the DNA to the poles during cell division

cytoplasm – contains enzymes that catalyse the chemical reactions of metabolism and DNA in a region call the nucleoid. Site for metabolic reactions

flagella - structures protruding from the cell wall with a corkscrew shape, using energy, they can be rotated, to propel the cell from on area to another unlike eukaryotic flagella, they are solid and inflexible, working like a propeller

ribosomes – synthesize proteins by translating messenger RNA. Some proteins stay in the cell and others are secreted

nucleoid– contains naked DNA which stores the genetic information that controls the cell and is passed on to daughter cells

pili - protein filaments protruding from the cell wall used for cell to cell adhesion when bacteria stick together to form aggregations of cells when two cells are exchanging DNA during conjugation

Plasmids -Extra-nucleoid DNA . Plasmids can self-replicate particularly before binary fission. They are associated with conjunction which is horizontal gene transfer.

Identify structures from an electron micrographs of E. coli shown on the next slide.

Electron micrographs of E. coli.

Reproduction of prokaryotic cells by binary fission

Prokaryotic cells divide by binary fission.

This is an asexual method of reproduction in which a 'parental' cell divides into two smaller but equally sized cells. The cells are genetically identical and form the basis of a reproductive clone.

Review Questions:Q. 1 How do prokaryotic cells divide?A. By mitosisB. By meiosisC. By buddingD. By binary fission

Q.2 Which function is carried out by the flagellum of the prokaryote?A. Movement of food towards the cellB. Movement of the whole cell from one place to anotherC. Movement of naked nucleic acid inside the cellD. Movement of water around the cell to speed up gas exchange

Questions 3 and 4 refer to the following micrograph of an E.coli bacterium undergoing reproduction.

Q. 3 The scale bar represents 0.5 µm. How long are both cells in total?A. 5.0 x 10- 6 mB. 5.0 x 10- 9 mC. 2.5 x 10- 6 mD. 2.5 x 10- 9 m

Q. 4 In the diagram what does label X identify?A. Nucleoid regionB. ChromatinC. HistonesD. Endoplasmic reticulum

Q. 5 (b) Distinguish between prokaryotic cells and eukaryotic cells. [6](b) Draw and label a diagram of the ultrastructure of Escherichia coli. [6](c) Annotate your diagram in (5) (b) above with functions of each part labelled. [6]