Practice Exam 1

Question 1

Clavulanic acid is?

Answer 1

compound added to antibiotics to inhibit β-lactamases produced by bacteria

Question 2

Lederberg and Tatum preformed experiments that conclusively demonstrated for the first time that?

Answer 2

bacteria can exchange genetic info leading to new phenotypes

Question 3

Bacteria having a single mutation resulting in loss of FLH-C function would:

Answer 3

be unable to express class 2 flagellular genes

Question 4

Bacterial cell has acquired mutation in its gene for DNA gyrase and has become resistant to an antibiotic. What class of antibiotics would it be resistant to?

Answer 4

Fluoroquinalones

Question 5

Why is E.coli O157;H7 such a dangerous problem compared to other E.coli strains?

Answer 5

It has a shiga toxin that results in severe disease

Question 6

The phylogenic tree of life divides life into domains based on?

Answer 6

Genetic relatedness based on rRNA sequences

Question 7

indetify the most accurate answer that describes features of the domain Archaea

Answer 7

Archaea are prokaryotic organisms with certain features in common with bacteria and eukaryota

Question 8

Peptidoglycan is found in the cell wall of gram positive bacteria, identify features of peptidoglycan:

Answer 8

held together via tetra-peptide linkages forming polymers of n-acetyl glucosamine and n-acteyl muramic acids

Question 9

A spontaneous mutation results in Listeria without LLO function, the result of this mutation is?

Answer 9

the trapping of a bacteria within an intracellular vacuole

Question 10

Bacterial plasmids..?

Answer 10

• apart of bacterial genome
• are extrachromosomal molecules

Question 11

Describe features of gram negative cell walls?

Answer 11

• composed of outer membranes with external polysaccharides
• composed of keto-dioxy kdo covalently linked to lipid A
• O-specific polysaccharides covalently linked to core polysaccharide

Question 12

Bacterial ribosome are often considered excellent targets for antibiotic therapy because?

Answer 12

The 30 and 50S subunits of the bacterial ribosomes are different from eukaryotic ribosomes.

Question 12

Bacterial endospores are formed in response to environmental stresses and result in differentiated cells. Describe endospores.

Answer 12

Resistant to high heat, desiccation (being dried), ultra violet light.

Question 13

Bacterial transcription occurs in the cytoplasm. Describe bacterial gene transcription?

Answer 13

RNA polymerase binds to promoter regions on DNA to promote mRNA synthesis

Question 14

Bacterial efflux pumps are best described as?

Answer 14

protein complexes used to pump out toxic compounds from the cell

Question 15

Describe features of AB-toxins

Answer 15

The B units exhibit binding specificity to allow toxin activity in specific cell types

Question 16

Describe Urea Cholera.

Answer 16

Expresses an AB toxin and a pilus that result in pathogenesis.

Question 17

AUG codon on sequence location helps in?

Answer 17

promoting open complex formation for protein translation

Question 18

bacterial capsules are best described as?

Answer 18

slimy protective coat on cell surface made of polysaccharides

Question 19

What is false regarding bacteria sigma factors?

Answer 19

• act to promote RNA translation at sp. DNA promoter elements
• provide specificity to RNA polymerase by binding to DNA promoter elements

Question 20

What is a likely outcome of random mutations combined with selective pressure on a bacterial species?

Answer 20

the bacteria that thrives will out-compete other bacteria due to the mutations

Question 21

When material cannot be heat treated for sterilization, what can be used to achieve biological sterility?

Answer 21

Radiation

Question 22

The U-tube experiment was pivotal in demonstrating what?

Answer 22

bacteria must make cell-cell contact to exchange plasmid DNA by conjugation

Question 23

Pathogenicity islands are best described as?

Answer 23

clusters of genes that encode info for virulence proteins

Question 24

How does Vibrio Chloera regulate its expression of AB toxin and pilus?

Answer 24

a transcriptional regulator activates both the toxin and the pilus gene expression at the same time

Question 25

SHORT ANS QUESTIONS

Question 26

1. An antibiotic that is know to be very effective at treating infections has suddenly become very ineffective when used by physicians to treat patients. The antibiotic is unchanged and remains biochemically & biologically active (not degraded or altered). It enters and remains in the bacteria when given to ill patients. What is a likely explanation for this change in drug efficacy? Why has a loss of drug efficacy occurred? What can be done to treat the infection?

Answer 26

• the drug can no longer interact or bind to its target within the bacterial cell hence loss of drug efficacy
• the target of the drug is likely changed by mutation rendering the target different (so drug is ineffective)
• treat with another drug ideally towards a different target or use combination therapy w/ other drugs to treat the infection

Question 27

Describe three biological mechanisms that bacteria use to resist antibiotic activity. Be specific and state how each mechanism operates to support antibiotic resistance.

Answer 27

1. mutation
   - changes protein target or biological structure so drug cannot inhibit the target
2. biofilm production or capsular polysaccharide
   - generates protective layer when exposed to sub-lethal concentrations to antibiotic allowing for survival and growth
3. efflux pumps
   - pumps antibiotic out of bacterial cell so it cannot interact with its usual cellular target (displacement)
4. beta lactamases
   - acts to cleave the b-lactam ring rendering the antibiotic inactive

Question 28

Differentiate by defining (do not compare) transaction, comptenance and conjugation with respect to DNA transfer in bacteria. You answer should reflect strong understanding of how DNA is acquired in each process.

Answer 28

Comptenance
- the ability to uptake free/naked/uncomplexed DNA from the environment or surroundings by bacterial cell

Conjugation
- DNA transfer, usually by plasmid, between two bacteria that requires cell-cell contact often leading to new phenotype (ex: antibiotic resistance)

Transduction
- lateral DNA transfer between two bacteria that requires bacteriophages
- bacteriophages acts to package DNA from one cell and infect another bacterial cell delivering DNA

Question 29

A team has sanitized surgical instruments by washing them in bleach and drying them in (100 degrees celcuis) hot oven for 5 minutes. Why should you be specifically concerned about these ‘santized’ instruments? What should the dentist do to do surgical instruments and how can that be achived? Why is bleach sanitization not satisfactory for oral surgery?

Answer 29

• You should be concerned about infection arising from contaimined surgical instruments
• the dentist needs to sterilize the instruments, this should be achieved by autoclaving (heat sterilization by steam reaching 121 degrees celcuis) which helps to inactivate spores
• bleach sanitization does not inactivate or kill endospores

Question 30

A terrible outbreak of Listeria oasis is reported in Toronto ON. You are working as the scientific officer for the food company linked to the outbreak. The news reporter contacts you and wants to know about Listeriosis and what causes the disease. The reporter did some homework before calling you and already knows about internalization, but now wants to know more about the ‘Listeria-pot’ and why this is important for disease progression. Outline the mechanisms that promote cell replication and intercellular spreading of Listeria. For full marks, you must name the protein and its origin that ‘propels’ Listeria and indentify some hallmark features of the Listereio pot with respect to intercellular spreading.

Answer 30

• Listeria produces LLO to degrade vacuole, gaining access to cytoplasm to promote replication.
• Listeria produces ActA proteins, which are virulence factors. ActA hijacks host cell actin.
• The outcome is actin-based motility that pushes the bacteria (aka listeria-pod) against the cell membrane, eventually exiting the cell and then enters an adjacent cell
• A hallmark feature of ‘Listerio-pod’ with respect to intracellular spreading is the presence of a double membrane vacuole in the new adjacent cell*

*take membrane from old cell and new cell hence the double membrane