MODULE 2

Question 1

What are the main shapes of prokaryotic cells?

Answer 1

Cocci, rods, bacillus, spirals, filaments (single cells joined together).

Question 2

Why do small cells have an advantage in some environments?

Answer 2

Higher surface area: volume ratio, therefore more efficient access to nutrients/substrates
particularly in low nutrient environments

Question 3

What is the main function of a cytoplasmic membrane?

Answer 3

• separation of cell constituents from environment

- selectively permeable: controlling substances coming into and out of the cell).

Question 4

How do bacterial and archaeal cytoplasmic membranes differ?

Answer 4

• 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

Question 5

What is likely to happen to a freshwater bacterium put into a high salt environment?

Answer 5

Water flows out of the cell by osmosis and would undergo plasmolysis (shrink).

Question 6

How does diffusion differ to active transport?

Answer 6

Requires energy and moves the substance against a concentration gradient

Question 7

What is the importance of the outer membrane of Gram negative bacteria?

Answer 7

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.

Question 8

Where is the periplasmic space of Gram negative bacteria?

Answer 8

• 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

Question 9

What is the structure of the major component of bacterial cell walls?

Answer 9

*Review structure of peptidoglycan from lectures

Question 10

What is the main difference between gram positive and gram negative cell walls?

Answer 10

Main difference is the amount of peptidoglycan and the outer membrane of the Gram negative wall.

Question 11

Penicillin is used to treat bacterial infections, especially those from gram positive bacteria. Why is penicillin non-toxic to us?

Answer 11

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.

Question 12

Why are gram positive bacteria generally more sensitive to penicillin?

Answer 12

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.

Question 13

When treated with lysozyme in isotonic solutions, gram positive bacteria form protoplasts and gram negative bacteria form spheroplasts. Why? What is the difference?

Answer 13

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.

Question 14

How do bacterial and archaeal cell walls differ?

Answer 14

• 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

Question 15

What are flagella?

Answer 15

External appendages for movement

*review structure of flagella from lectures

Question 16

Name some other types of structures for movement in prokaryotes?

Answer 16

• Axial filaments
• Gas vacuoles
• Magnetosomes

Question 17

How could you show that a bacterium produced endospores?

Answer 17

• Test for heat resistance, e.g. survival at 90-100°C

- Stain with malachite green (endospore stain procedure)

Question 18

Why are bacterial spores important?

Answer 18

• 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

Question 19

Name some other survival structures of prokaryotes.

Answer 19

• Cysts

- Inclusion bodies & storage granules e.g. polyphosphate, sulfur, polyhydroxybutyrate

Question 20

Why is glycocalyx of importance in the infectious process of pathogenic microbes?

Answer 20

• 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

Question 21

What is the role of an inclusion body in a bacterial cell?

Answer 21

Usually used for storing nutrient and/or energy sources

Question 22

Suppose microbial life was found on Mars. Assuming the organisms were similar to Earth microbes, what would be possible structural characteristics of these organisms?

Answer 22

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

Question 23

What are silent mutations and why do they occur?

Answer 23

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.

Question 24

What is a frameshift mutation?

Answer 24

A mutation caused by the addition or deletion of one or more bases in the DNA

Question 25

Explain the process of DNA transformation.

Answer 25

The process in which genes are transferred from one bacterium to another as DNA fragments in solution. Competent cells have DNA binding proteins to transport DNA strand into cell and then integrated in to recipient chromosome

Question 26

What two key findings came out of Frederick Griffith’s classic experiment?

Answer 26

• First demonstration of transformation
• Showed the importance of capsules of the infection process by preventing phagocytosis of Streptococcus pneumoniae cells

Question 27

Distinguish between generalised and specialised transduction.

Answer 27

• Transduction is DNA transfer from donor cell to recipient cell via bacteriophages
• Generalised: random fragments of the chromosome are packaged into phage particles and transferred
• Specialised: specific regions of the chromosome adjacent to a prophage are transferred following induction of a lysogenic infection by temperate virus

Question 28

What is the Ames test?

Answer 28

A test for carcinogenicity of chemical compounds. Measures reversion of histidine auxotrophs of Salmonella in response to the exposure to a mutagen/carcinogen.

Question 29

What is the difference between conjugation by F+ and Hfr donor cells?

Answer 29

Conjugation is the transfer of DNA by direct contact. F+ donors have F plasmid (F factor) separate to chromosome and just transfer the plasmid. Hfr donors have F plasmid integrated into the chromosome and transfer only part of the plasmid and part of the chromosome to recipient.

Question 30

The CRISPR system is said to protect genome integrity in prokaryotic cells by acting as a type of “immune system.” Explain how the CRISPR system works.

Answer 30

The CRISPR system is based on a region of the genome that contains DNA sequences from previously encountered foreign DNA separated by short palindromic repeats. The CRISPR region is translated into a long RNA molecule and then cleaved at each repeat to create short RNA molecules (crRNAs) that are complementary to foreign nucleic acids. If the crRNA binds to a piece of nucleic acid, associated proteins called Cas proteins will destroy the foreign nucleic acid and prevent it from recombining with the genome or replicating