What are the main shapes of prokaryotic cells?
Cocci, rods, bacillus, spirals, filaments (single cells joined together).
Why do small cells have an advantage in some environments?
Higher surface area: volume ratio, therefore more efficient access to nutrients/substrates
particularly in low nutrient environments
What is the main function of a cytoplasmic membrane?
- separation of cell constituents from environment
- selectively permeable: controlling substances coming into and out of the cell).
How do bacterial and archaeal cytoplasmic membranes differ?
- ester (bacterial) vs ether (archaea) linked lipids
- archaea often have mono-lipids rather than a bilayer
- unique lipids (hydrocarbons – isoprenoids)
- branched lipid structure in archaea
What is likely to happen to a freshwater bacterium put into a high salt environment?
Water flows out of the cell by osmosis and would undergo plasmolysis (shrink).
How does diffusion differ to active transport?
Requires energy and moves the substance against a concentration gradient
What is the importance of the outer membrane of Gram negative bacteria?
The lipopolysaccharide contains O antigens (protection against host defences), core
polysaccharide (negative charge – important in attachment), lipid A (exotoxin). The outer
membrane confers virulence to Gram negative bacteria.
Where is the periplasmic space of Gram negative bacteria?
- periplasm = substance that occupies periplasmic space
- usually the gap between cytoplasmic (plasma) membrane and outer membrane in gramnegative
bacteria. Sometimes also describes the gap between cytoplasmic membrane and cell wall in gram-positive bacteria
What is the structure of the major component of bacterial cell walls?
*Review structure of peptidoglycan from lectures
What is the main difference between gram positive and gram negative cell walls?
Main difference is the amount of peptidoglycan and the outer membrane of the Gram negative wall.
Penicillin is used to treat bacterial infections, especially those from gram positive bacteria. Why is penicillin non-toxic to us?
It stops production of peptidoglycan by preventing cross-linking of sheets. Therefore it is not toxic to humans because we do not have peptidoglycan in our cells.
Why are gram positive bacteria generally more sensitive to penicillin?
Gram positive cell envelopes are made up of mainly peptidoglycan so they are more sensitive than Gram negative walls. The outer membrane of the gram negative wall also provides extra protection and slows diffusion of penicillin.
When treated with lysozyme in isotonic solutions, gram positive bacteria form protoplasts and gram negative bacteria form spheroplasts. Why? What is the difference?
Lysozyme completely breaks down cell wall in gram positives to form protoplasts (no wall just membrane). The outer membrane of gram negative limits movement of lysozyme in, therefore wall often is only partially broken down to form spheroplasts.
How do bacterial and archaeal cell walls differ?
- More variation in Archaea than Bacteria, which just have peptidoglycan
- Most common cell walls in Archaea are protein/glycoprotein (S-layer) outside membrane or pseudomurein (similar to peptidoglycan) with N-acetyltalosaminouronic acid (NAT) and N-acetylglucosamine (NAG), and peptides
- Others can have polysaccharides
What are flagella?
External appendages for movement
*review structure of flagella from lectures
Name some other types of structures for movement in prokaryotes?
- Axial filaments
- Gas vacuoles
- Magnetosomes
How could you show that a bacterium produced endospores?
- Test for heat resistance, e.g. survival at 90-100°C
- Stain with malachite green (endospore stain procedure)
Why are bacterial spores important?
- Provide resistance and survival in adverse conditions for bacteria that produce them.
- Important in the food industry particularly heat treated foods e.g. canning, pasteurisation, can cause spoilage and food poisoning e.g. B.cereus, C.botulinum
- Spores are also important in wound infections, e.g. C. tetani (tetanus), C. perfringens (gas gangrene)
- Some strains have been used in bioterrorist activity, e.g. B.anthracis (anthrax).
- Some strains produce important biopesticides, e.g. B.thuringiensis
Name some other survival structures of prokaryotes.
- Cysts
- Inclusion bodies & storage granules e.g. polyphosphate, sulfur, polyhydroxybutyrate
Why is glycocalyx of importance in the infectious process of pathogenic microbes?
- Various external viscous polymer material (polysaccharides or glycoproteins) that surrounds the bacterial cell wall/outer membrane, collectively called glycocalyx (usually a capsule or slime layer)
- Allows adherence to surfaces and tissues
- Difficult to remove and treat e.g. more resistant to antibiotics, immune system
What is the role of an inclusion body in a bacterial cell?
Usually used for storing nutrient and/or energy sources
Suppose microbial life was found on Mars. Assuming the organisms were similar to Earth microbes, what would be possible structural characteristics of these organisms?
Survival, resistance and attachment structures would all be important. Review these structures and come up with your own answer. There is no right/wrong answer
What are silent mutations and why do they occur?
A mutation that occurs with a change in the DNA base sequence but there is no change in the protein encoded by that gene. Commonly occur when one nucleotide is substituted for another in the DNA.
What is a frameshift mutation?
A mutation caused by the addition or deletion of one or more bases in the DNA
