Ch 11: Catabolism Energy Release and Conservation

What are the two main energy sources for microorganisms?

Light (phototrophs) and oxidation of chemical compounds (chemotrophs).

What is the electron source for lithotrophs?

Reduced inorganic substances.

What carbon source do heterotrophs use?

Organic molecules.

Name the four major nutritional types of microorganisms.

Photolithoautotrophs, photoorganoheterotrophs, chemolithoautotrophs, chemoorganoheterotrophs.

Which microorganisms are representative of photolithoautotrophs?

Purple and green sulfur bacteria, cyanobacteria, diatoms.

What energy source do photoorganoheterotrophs use?

Light.

What carbon source do chemolithoautotrophs use?

CO₂.

Which microorganisms are representative of chemolithoautotrophs?

Sulfur-oxidizing bacteria, hydrogen-oxidizing bacteria, methanogens, nitrifying bacteria, iron-oxidizing bacteria.

What is the primary energy currency used by cells?

ATP.

What is reducing power in cells?

Molecules that serve as a supply of electrons for chemical reactions.

What are precursor metabolites?

Organic molecules used for biosynthesis of important chemical building blocks (monomers).

What are the three basic needs of all organisms?

ATP, reducing power, precursor metabolites.

What can chemoorganotrophs do for energy production?

Fermentation, aerobic respiration, anaerobic respiration.

What electron acceptors can be used in anaerobic respiration?

S°, NO₃⁻, SO₄²⁻, organic electron acceptors.

What is the terminal electron acceptor in aerobic respiration?

Oxygen (O₂).

What is the difference between aerobic and anaerobic respiration?

Aerobic uses O₂ as the terminal electron acceptor; anaerobic uses other acceptors like NO₃⁻ or SO₄²⁻.

How is ATP synthesized in fermentation?

Substrate-level phosphorylation (SLP).

Does fermentation involve an electron transport chain (ETC)?

No.

What is the main energy source for chemoorganotrophs?

Oxidized organic compounds.

What happens to the organic energy source in chemoorganotrophs?

It is oxidized, releasing energy (catabolism) and providing carbon and electrons for anabolism.

What are the two possible fates of electrons released during oxidation in chemoorganotrophs?

Donated to ETC (respiration) or endogenous acceptor (fermentation).

What is oxidative phosphorylation?

ATP synthesis using energy derived from the proton motive force (PMF).

What is the proton motive force (PMF)?

Potential energy from a proton gradient and membrane potential, used to power ATP synthesis.

What are the three central metabolic pathways for glucose degradation?

Embden-Meyerhof Pathway (EMP), Entner-Doudoroff Pathway (ED), Pentose Phosphate Pathway (PPP).

Which pathway is the most common for glucose degradation?

Embden-Meyerhof Pathway (EMP, glycolysis).

What are the two phases of glycolysis (EMP)?

Six-carbon phase (uses ATP) and three-carbon phase (makes ATP).

What is the key intermediate in the Entner-Doudoroff Pathway (ED)?

2-keto-3-deoxy-6-phosphogluconate (KDPG).

What is the main purpose of the Pentose Phosphate Pathway (PPP)?

Produces NADPH and ribose-5-phosphate for biosynthesis.

Does the Pentose Phosphate Pathway (PPP) depend on oxygen?

No, it is not oxygen-dependent.

What is the first step in the TCA cycle?

Pyruvate is decarboxylated to form acetyl-CoA, releasing CO₂ and generating NADH.

What molecule combines with acetyl-CoA to start the TCA cycle?

Oxaloacetate.

How many NADH molecules are produced per turn of the TCA cycle?

Three.

What is produced when succinyl-CoA is converted to succinate in the TCA cycle?

GTP (or ATP).

What is the final product of the TCA cycle?

Oxaloacetate (regenerated to restart the cycle).

What is the role of the electron transport chain (ETC)?

To transfer electrons from donors like NADH and FADH₂ to O₂, generating a proton motive force.

What are the four main types of electron carriers in the ETC?

Flavoproteins (FP), ubiquinone (UQ), cytochromes, nonheme iron-sulfur proteins (FeS).

What is Complex I in the mitochondrial ETC?

NADH-ubiquinone oxidoreductase.

What connects Complex I to Complex III in the ETC?

Coenzyme Q (CoQ).

What is the role of Complex IV in the ETC?

Cytochrome c oxidase, which transfers electrons to O₂ to form water.

How does E. coli's ETC differ under high and low oxygen conditions?

High O₂: bo branch (lower affinity); low O₂: bd branch (higher affinity).

What is ATP synthase?

A membrane-bound enzyme that makes ATP using the proton motive force (PMF); protons flow into the matrix (mitochondria) or into the cytoplasm (bacteria).

What are the two parts of ATP synthase?

F₀ (proton channel) and F₁ (catalyzes ATP synthesis).

What is the theoretical maximum ATP yield from aerobic respiration in eukaryotes?

30 ATP.

What is the P/O ratio for NADH?

2.5.

What is the P/O ratio for FADH₂?

1.6.

What are some common electron acceptors in anaerobic respiration?

NO₃⁻, SO₄²⁻, CO₂, S⁰, Fe³⁺.

What is the reduced product when sulfate (SO₄²⁻) is used as an electron acceptor?

H₂S.

What is the reduced product when CO₂ is used as an electron acceptor?

CH₄ (methane) or acetate.

What is fermentation?

Partial oxidation of an energy source without an ETC, using an endogenous electron acceptor.

Does fermentation generate a proton motive force (PMF)?

No.

What is the role of NAD⁺ in fermentation?

It is reduced to NADH during glycolysis and must be regenerated to NAD⁺ for glycolysis to continue.

What are the three types of fermentation pathways?

Mixed acid, butanediol, alcoholic acid.

What is an example of a mixed acid fermenter?

E. coli.

What is an example of a butanediol fermenter?

Enterobacter.

What are some products of fermentation used in food production?

Alcoholic beverages, yogurt, cheese, bread.

How are disaccharides cleaved into monosaccharides?

By hydrolases (extracellular) or phosphorylases (intracellular).

What enzyme cleaves lactose into glucose and galactose?

β-galactosidase.

What is chemolithotrophy?

The use of reduced inorganic compounds as a source of energy and electrons.

What are common energy sources for chemolithotrophs?

Hydrogen (H₂), reduced nitrogen compounds, reduced sulfur compounds, ferrous iron (Fe²⁺).

What is the terminal electron acceptor for most chemolithotrophs?

O₂, but sulfate and nitrate may also be used.

Do chemolithotrophs use fermentation?

No.

What is reverse electron flow in chemolithotrophs?

The process of reducing NAD⁺ to NADH at the expense of PMF.

Why is reverse electron flow necessary for chemolithotrophs?

To generate NADH for biosynthetic reactions when the electron donor has a less negative redox potential than NAD⁺.

What enzyme do hydrogen-oxidizing bacteria use to transfer electrons from H₂?

Hydrogenase.

What is the role of nitrifying bacteria?

To oxidize reduced nitrogen compounds like NH₄⁺ to NO₂⁻ or NO₃⁻.

What are the three major groups of chemolithotrophs with ecological importance?

Hydrogen-oxidizing bacteria, nitrifying bacteria, sulfur-oxidizing bacteria.

What is the difference between phototrophs and chemotrophs?

Phototrophs use light as an energy source; chemotrophs use chemical compounds.

What is the difference between organotrophs and lithotrophs?

Organotrophs use organic compounds as electron sources; lithotrophs use inorganic compounds.

What is the difference between heterotrophs and autotrophs?

Heterotrophs use organic carbon; autotrophs use CO₂.

What is the role of the TCA cycle in metabolism?

To completely oxidize acetyl-CoA to CO₂, generate NADH/FADH₂, and provide precursor metabolites.

What is the net ATP yield from glycolysis (EMP)?

2 ATP.

What is the net NADH yield from glycolysis (EMP)?

2 NADH.

What is the net ATP yield from the TCA cycle per glucose molecule?

2 GTP (or ATP).

What is the net NADH yield from the TCA cycle per glucose molecule?

6 NADH.

What is the net FADH₂ yield from the TCA cycle per glucose molecule?

2 FADH₂.

What is the purpose of the glyoxylate cycle?

To bypass decarboxylation steps in the TCA cycle, allowing the use of acetyl-CoA for biosynthesis.

What is the role of transketolase and transaldolase in the PPP?

To catalyze sugar transformations for biosynthesis or regeneration of glucose-6-phosphate.

What is the difference between substrate-level phosphorylation and oxidative phosphorylation?

SLP directly synthesizes ATP from a substrate; oxidative phosphorylation uses PMF.

What is the role of methanol dehydrogenase in methylotrophs?

To oxidize methanol and donate electrons to cytochrome c.

What is the difference between obligate and facultative anaerobes?

Obligate anaerobes cannot tolerate O₂; facultative can switch between aerobic and anaerobic metabolism.

What is the role of nitrate reductase?

To reduce NO₃⁻ to NO₂⁻ or N₂.

What is the role of sulfate reductase in anaerobic respiration?

To reduce SO₄²⁻ to H₂S.

What is the role of carbon dioxide reductase in anaerobic respiration?

To reduce CO₂ to CH₄ or acetate.

What is the role of iron reductase in anaerobic respiration?

To reduce Fe³⁺ to Fe²⁺.

What is the role of the proton motive force (PMF) in flagellar rotation?

To power the rotation of bacterial flagella without ATP hydrolysis.

What is the function of flavoproteins (FP) in the electron transport chain?

They accept two electrons and two protons and pass electrons to the next carrier.

What is the role of ubiquinone (UQ) in the ETC?

It is a lipid-soluble electron carrier that transports 2 electrons and 2 protons between Complexes I/II and III.

What type of protein are cytochromes?

Heme-containing proteins that transfer electrons via iron atoms.

What is the role of nonheme iron-sulfur proteins in the ETC?

They transfer electrons between carriers using iron-sulfur clusters.

How does the Q cycle in Complex III contribute to the proton motive force?

It transfers electrons while pumping protons across the membrane, increasing PMF.

What are the three components of the proton motive force?

Chemical gradient (ΔpH), electrical potential (Δψ), and the proton gradient itself.

How do microbes conserve energy during anaerobic respiration?

By using alternative terminal electron acceptors with lower redox potential than oxygen.

What are the environmental impacts of sulfate-reducing bacteria?

Production of H₂S, which can cause corrosion and toxicity in ecosystems.

How do methanogens produce methane?

By reducing CO₂ with electrons derived from H₂ or other substrates.

What is the function of the glyoxylate cycle?

It bypasses decarboxylation steps in TCA to allow growth on acetate or fatty acids.

What is the role of phosphofructokinase in glycolysis?

Catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate; a key regulatory step.

What are common fermentation products used in industry?

Ethanol, lactic acid, acetone, and butanol.

What is the function of the enzyme lactate dehydrogenase?

Converts pyruvate to lactate during fermentation, regenerating NAD⁺.

How do chemolithoautotrophs fix carbon?

Using the Calvin cycle powered by energy from inorganic electron donors.

What is the difference between obligate and facultative chemolithotrophs?

Obligate chemolithotrophs require inorganic substrates; facultative can switch to organic substrates.