Answer these questions with a few short sentences, or in dot points. Sometimes d

Question

Answer these questions with a few short sentences, or in dot points. Sometimes diagrams are a good way to answer the question, if so be sure to use labels and explain the diagram. (Generally ,1 mark per fact.)

1. How does Cholera toxin exert its effects? (3 marks) ( or Diptheria toxin, or Botulinum toxin) Use a diagram. What kind of toxins are these?

2. Why is PCR frequently used for detecting or confirming viral infections? (2 marks)

3. Some bacteria are able to inhibit phagolysosomal fusion. What does this mean and why is this ability considered a virulence factor? (4 marks)

4. What is the difference between a local infection and a systemic infection? (1 marks)

5. What enzyme that assists growth in the urinary tract do all of the following organisms possess?mirabilis,?Ureaplasma urealyticum, S. saprophyticus

Explanation / Answer

1. Cholera toxin is released into the intestine by the bacteria. It binds to the receptors on enterocytes (pentameric B subunit of the toxin binds to GM1 ganglioside receptor). The entire complex is then endocytosed and A1 subunit is released into the cell. A sequence of events activates Arf6 which ultimately results in the activation of adenylate cyclase thereby increasing the intracellular cAMP levels. The increased cAMP levels activate PKA which phosphorylates CFTR chloride channel proteins. The activated CFTR channel releases H2O, Na+, Cl-, HCO3- into the intestinal lumen. The ultimate effect is the fluid loss (up to2L per hour). SYmptoms include rice-water stool and dehydration.

2. PCR is avery sensitive technique. It can be used to detect the presence minute amounts of template DNA in the host. Hence it can be used to detect viral infections.

3. Several bacteria such as mycobacteria inhibit the fusion of phagosome with lysosome. This ensures that the phagocytosed pathogen can not be degraded. Hence it is considered as a virulence factor.

4. A local infection is confined to a specific organ or tissue. A systemic infection is spread/found in all parts of the body.

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