Mircrobiology - Bacteria

Question 1

What is ribosome structure in Bacteria and Eukaryotes

Answer 1

1. Bacteria - 70S ribosome (50S and 30S subunits)

2. Eukaryotes - 80S ribosome (60S and 40S subunits)

Question 2

What the different bacteria shapes? (7)

Answer 2

1. Coccus (Round)
2. Bacillus (Long - Rod shaped)
3. Cocobacillus (Round but long)
4. Fusiform Bacillus (Oval Long)
5. Vibrio (Curved)
6. Spirillum (Spiral)
7. Spirochete (Very Spiral)

Question 3

Describe gram-positive bacterium (4)

Answer 3

Gram-positive:

1. Purple stain.
2. Only has a cell wall made of Beta lactamase with thick peptidoglycan layer.
3. Penicillin-binding protein in Cytoplasmic membrane.
4. Lipoteichoic acids in cell wall.

Question 4

Describe gram-negative bacterium (4)

Answer 4

Gram-negative:

1. Pink stain
2. Outermembrane of Lioppolysaccharide, Porin channel and beta lactamse layer.
3. Cell wall made of thin peptidoglycan.
4. Penicillin-binding protein.

Question 5

What is the structure of peptidoglycans? (3)

Answer 5

1. 3 Dimensional Polymer
2. Made up of N-acetylated sugars: glucosamine (NAG) and muramic acid (NAG) AND 5 amino acid peptides.
   (amino acids make it resistant to enzyme destruction)
3. Cross-linked by Transpeptidase enzymes.

Question 6

What are the peptidoglycan synthesis pathways unique to bacteria? These steps are important antibiotic targets (3)

Answer 6

1. Polymerisation of sugars (for making backbone)
2. Elongation of Amino acid side chains (to make peptides.
3. Transpeptidase (for cross-linking)

Question 7

What is the structure of Lipopolysaccharide (aka endotoxin)? (3)

Answer 7

1. Long-chain fatty acid anchor (Lipid A) (active component)
2. Core polysaccharide chain
3. Variable CHO chain (=O antigen)

Question 8

What are the functions of Lipopolysaccharide? (3)

Answer 8

1. Major structural component of gram negative
2. Effective permeability barrier (including to antimicrobials)
3. Modulates host immune response.

Question 9

What bacteria do not have a cell wall?

Answer 9

1. M. pneumonia (pneumonia) and Urea plasma. These cannot be cultured or stained.
2. Mycobacteria - have a very think lipid membrane made of mycolic acids which affect gram staining. This allows intracellular survival. ZN stain is used instead.
3. Chlamydia trachomatis

Question 10

What are the 3 ways Bacteria can grow? (2)

Answer 10

1. Clusters e.g gram positive staphylococci
2. Chains e.g gram positive streptococci
3. Spores

Question 11

How can bacterial growth be exploited to be identified? (3)

Answer 11

1. Growth in chains or clusters, as well as size/shape when cultured.
2. Enzymes, waste products excreted
3. Growth requirements such as nutrients and atmosphere.

Question 12

How can bacteria be classed based on atmospheric requirement?

Answer 12

1. Aerobes - Uses O2
2. Anaerobes - Use Fermentation, O2 usually toxic.
3. Facultative Anaerobes - Can switch between Aerobes and Anaerobes metabolism.

Question 13

What are some nutritional requirements of Bacteria? (3)

Answer 13

1. Mostly Purines and Pyrimidines, amnio acids and vitamins.
2. Escherichia Coli need just glucose and inorganic salts, so very easy to grow in lab.
3. Treponema Pallidum (Syphillis) needs a specialised enriched medium so very hard to grow.

Question 14

What are some Physical requirements for bacterial growth? (3)

Answer 14

1. Temperature
2. pH
3. Salt Content

Question 15

Describe the capsule of the bacteria (4)

Answer 15

1. Polysaccharide coat to hide immunogenic cell wall.
2. Immunity requires antibodies to capsule
3. It has metabolic burden on bacterium
4. It confers virulence e.g Haemophilus Influenzae

Question 16

What are the different ways bacteria can move? (4)

Answer 16

1. Chemotaxis - movement based on chemical stimuli
2. Flagellum
3. Pilus - using to grap and pull
4. Corkscrew Motility e.g spirochete

Question 17

How can bacteria stick to surfaces? (3)

Answer 17

1. Docking (non-specific)
2. Anchoring (specific) - where it binds to a specific receptor, maybe by fimbriae or Pili. This confers tissue tropism and host specificity.
3. Biofilm formation - More resistant to immune response and antibiotics.

Question 18

How can Bacteria Propagate? (3)

Answer 18

1. Transduction - Introducing DNA to a recipient
2. Conjugation - directly binds to recipient and transfers genetic info.
3. Competence/transformation - dies and DNA is received by recipient.

Question 19

What are the 2 mobile genetic elements in bacteria?

Answer 19

1. Plasmids - Circular and extra-chromosomal DNA. They replicate independently and code for dozens of genes. Can be passed and transmitted by bacteria.
2. Transposons - DNA sequences that move location in genomic DNA and plasmids. They encode for transposase and other genes.

Question 20

Why are spores unique in bacterial growth?

Answer 20

1. They are non-replicating and dormant.
2. Resistant to drying, temp, disinfection and digestion.

This makes them important in clinical disease pattern and infection control.

Question 21

How can gene regulation help Bacteria survive? (3)

Answer 21

1. Conserving its energy
2. Adapting to environmental changes
3. Coordinated changes to multiple gene expression.

Question 22

What are the different phases of Bacterial growth? (4)

Answer 22

1. Lag phase: No increase in cell number when adjusting to new environment.
2. Exponential phase: Cell doubling
3. Stationary phase: Nutrients depleting, metabolites build up and division stops.
4. Death Phase: Exhaustion of resources when in toxic environment.