Q.9 Under stress conditions bacteria accumulate
- (A) ppGpp (Guanosine tetraphosphate)
- (B) pppGpp (Guanosine pentaphosphate)
- (C) Both ppGpp and pppGpp
- (D) Either ppGpp or pppGpp
Bacteria trigger the stringent response under nutrient starvation or stress, mediated by alarmones ppGpp (guanosine tetraphosphate) and pppGpp (guanosine pentaphosphate). Synthesized by RelA/SpoT, these nucleotides reprogram transcription, halting growth while boosting survival genes.
Stringent Response Mechanism
During amino acid famine, uncharged tRNAs activate RelA on ribosomes, producing (p)ppGpp. ppGpp inhibits rRNA synthesis (via RNA polymerase) and prioritizes stress genes like amino acid biosynthesis. Both forms accumulate dynamically, with pppGpp prominent early and ppGpp later.
Correct Answer: (C) Both ppGpp and pppGpp
Under stress, bacteria accumulate both ppGpp and pppGpp—collectively (p)ppGpp. Levels rise 10-20 fold, coordinating the global response in E. coli, B. subtilis, and pathogens.Explanation of All Options
Each choice reflects alarmone dynamics:
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(A) ppGpp (Guanosine tetraphosphate)
Incorrect alone. ppGpp dominates but pppGpp also accumulates, especially initially via RelA. -
(B) pppGpp (Guanosine pentaphosphate)
Incorrect alone. pppGpp forms first, but ppGpp follows via SpoT hydrolase activity. -
(C) Both ppGpp and pppGpp
Correct. Literature confirms dual accumulation during stringent response to starvation, heat, or antibiotics. -
(D) Either ppGpp or pppGpp
Incorrect. Stress induces both concurrently, not alternatively; ratios vary by condition/strain.
Option Accumulates? Role in Stress Key Enzyme (A) ppGpp Yes Inhibits growth genes RelA/SpoT (B) pppGpp Yes Early alarmone RelA (C) Both Yes Full stringent response Both synthetases (D) Either No Not exclusive N/A Applications in Microbiology
(p)ppGpp mutants fail stress adaptation, aiding antibiotic discovery. In biotech, it influences recombinant protein yields under stress. Analyze via thin-layer chromatography for research.
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