TOPIC 3A 4 PROKARYOTIC CELLS

What is the function of a bacterial cell wall ?

1. Prevents water from entering and bursting the cell via osmosis

2. Because the medium in bacteria is usually hypertonic to their environment

3. It also maintains the shape of the bacterium

4. And gives support and protects contents of cell

What is peptidoglycan ?

1. All bacterial cell walls have peptidoglycan,

2. It consists of parallel polysaccharide chains with short peptide cross-linkages,

3. Producing an enormous molecule with net-like structure

Asides from peptidoglycan, what may a bacteria have on its bacterial cell wall ?

1. A capsule,

2. It may be made of starch, protein, gelatin or glycolipid.

3. It protects the bacterium from white blood cells,

4. and covers the cell markers on the cell membrane that identify the cell.

How does a capsule effect the pathogenic ability of a bacterium ?

1. It makes it easier for bacterium to be pathogenic,

2. Because it is not easily identified by te immune system.

What else could the capsule be used for ?

1. To survive dry environments

What are Pili and what are they used for ?

1. Pili are thread-like protein projections from the bacteria’s cell surface.

2. They are used for attachment on host cells and sexual reproduction.

how do Pili make bacteria vulnerable ?

1. They may serve as points of attachment for bacteriophages.

How else can a bacteria move itself ?

1. Through flagella,

2. These are,many-stranded helix of the protein flagellin,

3. They move by rotating rapidly.

How does the cell surface membrane of bacterium differ from that of eukaryotic cells ?

1. The cell surface membrane of prokaryotic cells are similar both in function and in structure to eukaryotic cells.

2. However, bacteria have no mitochondria,

3. Therfore, the cell surface membrane is also the site of some respiration enzymes.

Some bacteria such as Bacillus subtilis have infoldings on their cell surface membrane, what are they called and what are their functions ?

1. They are mesosomes,

2. Some scientist think they are an artefact from preparing a cell for electron micrograph,

3. Others believe they are associated with enzyme activity, Particularly during the formation of new cell walls when the bacteria divide.

4. Or it may be used for photosynthesis.

What is a nucloid ?

1. The coiled and tangled DNA of the bacterium,

2. It is not contained in a membrane-bound nucleus.

What are plasmids ?

1. Plasmids are the other smaller circles of DNA,

2. That exist separately from the nucloid.

3. It codes for a specific phenotype of the bacterium,

4. It can be transfer from one bacterium to another in a form of sexual reproduction using Pili.

Explain the 70S ribosomes present in bacteria ?

1. That is where protein synthesis occurs,

2. It has a larger 50S subunit and a smaller 30S subunit.

What is gram-positive bacteria ?

1. Bacteria are usually colorless, gram staining allows us to tell how vulnerable they are.

2. Gram-positive bacteria have a thick peptidoglycan layer on their cell surface membrane,

3. Which contains teichoic acid within the net-like structure.

4. The crystal violet complex is trapped in the peptidoglycan layer and resists decoloring,

5. When dehydrated with alcohol.

6. As a result the bacteria do not pick up the red safranin counterstain and appear purple when viewed under a light microscope.

What is gram-negative bacteria ?

1. Gram-negative bacteria has an outer membrane and a inner membrane,

2. In between is a thin peptidoglycan layer, with no teichoic acid.

3. The outer membrane is made of lipopolysaccharides,

4. It is dissolved when the bacterium is dehydrated in ethanol,

5. This exposes the thin peptidoglycan layer and the violet crystal complex is washed off

6. The bacteria takes up the red safranin counterstain and appears red under a microscope.

How do we classify bacteria via shape ?

1. Spherical bacteria are cocci

2. Rod-shaped bacteria are bacilli

3. Twisted bacteria are spirilla

4. Comma-shaped bacteria are vibrios

How do we classify bacteria via their respiratory requirements ?

1. Obligate aerobes require oxygen for respiration

2. Facultative anaerobes can use oxygen if available, but can manage without it

3. Obligate anaerobes can only respire without oxygen, oxygen will kill them.