A pharmaceutical company has modified one of its existing antibiotics to have an improved toxicity profile. The new antibiotic blocks protein synthesis by first entering the cell and then binding to active ribosomes. The antibiotic mimics the structure of aminoacyl-tRNA. The drug is covalently bonded to the existing growing peptide chain via peptidyl transferase, thereby impairing the rest of protein synthesis and leading to early polypeptide truncation. Where is the most likely site that this process occurs?
AE site
B30S small subunit
CA site
D40S small subunit
EP site
A stool sample was taken from a 19-year-old male who presented with profuse watery diarrhea. He recently returned from a trip to Central America. A microbiologist identified the causative agent as a gram-negative, oxidase-positive, comma-shaped bacteria that is able to grow well in a pH > 8. Which of the following is a mechanism of action of the toxin produced by this bacteria?
AOveractivation of adenylate cyclase by inhibition of Gi subunit by ADP-ribosylation
BInactivation of the 60S ribosomal subunit by cleaving an adenine from the 28S rRNA
COveractivation of guanylate cyclase
DOveractivation of adenylate cyclase by activation of Gs subunit by ADP-ribosylation
EDegradation of cell membranes by hydrolysis of the phospholipids
An investigator is studying collagen synthesis in human fibroblast cells. Using a fluorescent tag, α-collagen chains are identified and then monitored as they travel through the rough endoplasmic reticulum, the Golgi apparatus, and eventually into the extracellular space. Which of the following steps in collagen synthesis occurs extracellularly?
ATriple-helix formation
BTranslation of pro-α chains
CCleavage of procollagen C- and N-terminals
DGlycosylation of pro-α chains
EHydroxylation of proline and lysine
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