Microbial Infection and Pathogenesis - AB-Type Exotoxins

5 important questions on Microbial Infection and Pathogenesis - AB-Type Exotoxins

Define exotoxins and briefly explain the three categories mentioned in the text. Provide an example of a disease caused by each category.

Exotoxins are toxic proteins secreted by pathogens. The three categories are AB toxins, cytolytic toxins, and superantigen toxins. Examples include diphtheria (AB toxin), streptolysin (cytolytic toxin), and toxic shock syndrome toxin (superantigen toxin).

Describe the structure of AB toxins and their mechanism of action. Provide examples of AB toxins discussed in the text.

AB toxins consist of two subunits, A and B. The B subunit binds to a host cell surface molecule, facilitating the transfer of the A subunit, which damages the cell. Examples include diphtheria toxin, botulinum toxin, tetanus toxin, and cholera toxin.

Explain how diphtheria toxin functions in inhibiting protein synthesis. Discuss the significance of the viral gene tox in this process

Diphtheria toxin inhibits protein synthesis by blocking the transfer of an amino acid from tRNA to growing polypeptide chains. The viral gene tox, present in the genome of the lysogenic bacteriophage b, encodes diphtheria toxin. Toxigenic strains of C. diphtheriae are infected with phage b, producing the toxin.
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Contrast the mechanisms of action and symptoms of botulism and tetanus toxins. How do these toxins affect nerve impulses and muscle activity?

Botulinum toxin prevents muscle contraction by blocking neurotransmitter release, leading to flaccid paralysis. Tetanus toxin prevents muscle relaxation by blocking the release of inhibitory neurotransmitters, causing spastic paralysis and muscle contractions.

Describe how cholera enterotoxin functions and its impact on the human body. Explain the main treatment for cholera.

Cholera enterotoxin is an AB-type exotoxin produced by Vibrio cholerae. The B subunit binds to GM1 ganglioside in the intestinal epithelium, and the A subunit activates adenylate cyclase, leading to increased cAMP levels. This disrupts ion balance, causing watery diarrhea. Oral rehydration solution is the main treatment for cholera.

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