Discussion
Which one of the following metabolites is associated with bacterial stringent response?
Answer: B
The stringent response is associated with guanosine tetraphosphate (ppGpp).
When bacteria run short of amino acids, uncharged tRNAs enter the ribosome's A site and activate RelA, which makes (p)ppGpp, the 'alarmone'. ppGpp binds RNA polymerase and shuts down synthesis of rRNA and tRNA while switching on amino acid biosynthesis genes, so the cell saves resources until conditions improve.
The other nucleotides signal different things. Cyclic di-GMP controls the switch between motile and biofilm lifestyles; cAMP, with CRP, mediates catabolite repression; and cGMP is mainly a second messenger in eukaryotic cells. None of them is the mediator of the stringent response.
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