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Questions and Answers
The A subunit of diphtheria toxin inhibits protein synthesis by catalyzing which specific reaction?
The A subunit of diphtheria toxin inhibits protein synthesis by catalyzing which specific reaction?
- Dephosphorylating initiation factors.
- Methylating specific tRNA molecules.
- ADP-ribosylating elongation factor 2 (EF-2). (correct)
- Hydrolyzing peptide bonds within the ribosome.
Shiga toxin-producing Escherichia coli (STEC) exert their cytotoxic effects through what primary mechanism?
Shiga toxin-producing Escherichia coli (STEC) exert their cytotoxic effects through what primary mechanism?
- Inhibiting the synthesis of essential amino acids.
- Directly disrupting the host cell's plasma membrane integrity.
- Activating host cell caspases, leading to apoptosis.
- Depurinating a specific adenine residue in ribosomal RNA (rRNA). (correct)
What is the primary mechanism by which the B subunit of an AB toxin facilitates its entry into a host cell?
What is the primary mechanism by which the B subunit of an AB toxin facilitates its entry into a host cell?
- Disrupting the cell's cytoskeleton, allowing the A subunit to enter.
- Stimulating the production of host cell antibodies to promote uptake.
- Binding to specific receptors on the host cell surface, initiating endocytosis. (correct)
- Directly penetrating the cell membrane through hydrophobic interactions.
Which of the following best describes the role of acidification within the endocytic vesicle during the entry of AB toxins?
Which of the following best describes the role of acidification within the endocytic vesicle during the entry of AB toxins?
Hemolytic Uremic Syndrome (HUS) secondary to Shiga toxin-producing E. coli (STEC) infection primarily affects which organ system?
Hemolytic Uremic Syndrome (HUS) secondary to Shiga toxin-producing E. coli (STEC) infection primarily affects which organ system?
Shiga toxin-producing E. coli O157:H7 is most commonly associated with which of the following sources of infection?
Shiga toxin-producing E. coli O157:H7 is most commonly associated with which of the following sources of infection?
Following endocytosis of an AB toxin, what is the typical fate of the B subunit after the A subunit has been translocated into the cytoplasm?
Following endocytosis of an AB toxin, what is the typical fate of the B subunit after the A subunit has been translocated into the cytoplasm?
Which of the following is a key difference between Shiga toxin 1 and Shiga toxin 2?
Which of the following is a key difference between Shiga toxin 1 and Shiga toxin 2?
What is the significance of the observation that some patients infected with STEC develop HUS without experiencing diarrhea?
What is the significance of the observation that some patients infected with STEC develop HUS without experiencing diarrhea?
Which cellular process is most directly affected by the depurination of ribosomal RNA caused by Shiga toxin?
Which cellular process is most directly affected by the depurination of ribosomal RNA caused by Shiga toxin?
Flashcards
AB Toxins
AB Toxins
Proteins with two parts (A and B). The A portion is an enzyme (toxic part), and the B portion binds to host cell receptors.
Diphtheria Toxin Mechanism
Diphtheria Toxin Mechanism
The A toxin produced by Corynebacterium diphtheriae transfers ADP-ribose to elongation factor 2 (EF-2), thus stopping protein creation.
Shiga Toxin Mechanism
Shiga Toxin Mechanism
Shiga toxin disrupts protein synthesis by depurinating a specific RNA residue in ribosomal RNA.
Shiga Toxin Symptoms
Shiga Toxin Symptoms
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Hemolytic Uremic Syndrome (HUS)
Hemolytic Uremic Syndrome (HUS)
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STEC HUS Pathogenesis
STEC HUS Pathogenesis
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Shiga Toxin Source
Shiga Toxin Source
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Study Notes
- Bacterial cytotoxins inhibit protein synthesis
Bacteria Producing Cytotoxins
- Corynebacterium diphtheriae
- Shigella dysenteriae
- Escherichia coli (certain strains)
AB Toxins Mechanism
- AB toxins are proteins with two parts: A and B.
- The A portion is an enzyme that is the toxic part.
- The B portion binds to host cell receptors.
- After binding, the toxin is taken up via endocytosis.
- The vacuole becomes acidic, separating the A and B portions.
- The A portion enters the cytoplasm and exerts its toxic effect.
- The B portion is removed via exocytosis.
- Different microorganisms produce A toxins with different activities.
Corynebacterium Diphtheriae Toxin
- The A toxin produced by Corynebacterium diphtheriae transfers ADP-ribose to elongation factor 2 (EF-2).
- This inhibits protein synthesis.
- ADP ribosylation is a common action of AB toxins.
Shiga Toxin-Producing E. Coli (STEC)
- Also known as verocytotoxin-producing E. coli (VTEC) or enterohaemorrhagic E. coli (EHEC).
- Shiga toxin has two types: Shiga toxin 1 and Shiga toxin 2.
- The toxin is encoded by bacterial DNA.
- It contains one A subunit (active) and five B subunits (receptor-binding).
- The most common serotype associated with human disease is O157:H7.
- It causes more than 70,000 cases per year in the United States.
- Infective dose is low (less than 100 organisms).
Mechanism of Shiga Toxin
- Infection source: contaminated meat, water, meat juices, vegetables, etc.
- Shiga toxin induces depurination of a specific RNA residue in ribosomal RNA, disrupting protein synthesis and leading to cell death.
- Symptoms include watery diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS) in some cases.
Shiga Toxin and Hemolytic Uremic Syndrome (HUS)
- STEC HUS is a rare condition that mainly affects the kidneys.
- Children and the elderly are more at risk.
- In the UK, about 150 people a year develop STEC HUS.
- STEC strains carry genetic information for producing Shiga toxin.
- The toxin is released in the gut, passes into the bloodstream, and travels to the kidneys.
- It binds to cells lining blood vessels in the kidneys, causing damage.
- This leads to tiny blood clots, destroying red blood cells.
- Kidney function is impaired and other organs can be affected.
- Symptoms: diarrhea (possibly bloody), abdominal pain, reduced urine, weakness, pallor, body swelling, and headaches.
Multiple Choice Answers
- Diphtheria toxin acts by inhibiting protein synthesis.
- Corynebacterium diphtheriae and Escherichia coli produce exotoxins that act by ADP-ribosylation.
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