Energy Classes & Redox
Which type of microorganism uses inorganic compounds for energy and CO₂ as a carbon source?
Chemolithoautotroph
What type of phosphorylation produces ATP during glycolysis?
Substrate-level phosphorylation
What is the electron donor in oxygenic photosynthesis?
H₂O (water)
What is the function of the operator region in an operon?
DNA sequence where repressors bind to block RNA polymerase.
What small molecule activates CAP (CRP) to promote transcription?
cAMP
When one molecule is oxidized, another must be ___
Reduced; redox reactions occur in pairs
What is the role of the proton motive force (PMF) in oxidative phosphorylation?
Drives ATP synthase to convert ADP + Pi → ATP
What is the main product of cyclic photophosphorylation?
ATP only
If lactose is present but glucose is high, what happens to the lac operon?
Transcription remains low due to inactive CAP-cAMP (catabolite repression).
What event triggers the stringent response, and which molecule mediates it?
Amino acid starvation → RelA produces (p)ppGpp to inhibit rRNA and tRNA synthesis
Explain why electrons from NADH flow spontaneously to O₂ in aerobic respiration
Because NADH has a more negative reduction potential and O₂ has a more positive one, creating a favorable ΔE°′
Explain why fermentation generates less ATP than respiration.
Fermentation lacks an electron transport chain and relies solely on substrate-level phosphorylation.
Why do purple sulfur bacteria require reverse electron flow?
To generate NADH from low-potential donors like H₂S for biosynthetic reactions
In the arginine operon, what happens when intracellular arginine levels increase?
Arginine binds to the repressor (corepressor), blocking transcription.
Which global control system allows bacteria to sense population density?
Quorum sensing
If a bacterium uses H₂ as the electron donor and NO₃⁻ as the terminal acceptor, what kind of metabolism is this?
Chemolithotrophic anaerobic respiration
If oxygen becomes unavailable, how can a facultative anaerobe continue producing ATP?
By switching to fermentation or using an alternative acceptor like nitrate.
What would happen if photosystem II were blocked in cyanobacteria?
Cells would rely on cyclic photophosphorylation around PSI to make ATP but could not produce NADPH or O₂.
Explain why the ara operon is both positively and negatively regulated.
AraC acts as a repressor when arabinose is absent and as an activator when arabinose is present.
Describe the SOS response mechanism in E. coli
DNA damage activates RecA, which cleaves LexA repressor, inducing DNA repair genes
Compare the energy yield of H₂ → NO₃⁻ versus NADH → NO₃⁻. Which produces more energy, and why?
H₂ → NO₃⁻ produces more energy because H₂ has a lower (more negative) reduction potential, producing a greater ΔE°′
A culture loses cytochrome oxidase function but retains NADH dehydrogenase. Predict the effect on ATP yield.
ATP synthesis drops sharply; ETC is incomplete, and fewer protons are pumped, decreasing oxidative phosphorylation efficiency.
A chemolithotroph oxidizes Fe²⁺ and reduces O₂. Explain why this process releases little energy.
The redox potential difference between Fe²⁺ and O₂ is small, so ΔE°′ (and energy yield) is limited.
A mutation prevents the lac repressor from binding to the operator. Predict expression.
Constitutive expression; transcription occurs regardless of lactose presence.
Compare the regulation strategies of the heat-shock response and feedback inhibition
Heat-shock uses sigma factors and chaperones to refold proteins; feedback inhibition shuts down the first enzyme in a biosynthetic pathway by end-product binding