Q.1 Which of the following best defines a metabolic pathway?
A series of electrical signals transmitted through neurons
A linear chain of enzymatic reactions converting a substrate into a product
A set of genes that are co‑expressed under stress conditions
A network of protein–protein interactions governing cell division
Explanation - Metabolic pathways are sequences of enzyme‑catalyzed reactions where the product of one reaction becomes the substrate for the next.
Correct answer is: A linear chain of enzymatic reactions converting a substrate into a product
Q.2 In flux balance analysis (FBA), the objective function is usually chosen to:
Minimize the number of enzymes used
Maximize the production of ATP or biomass
Minimize the electrical resistance of the cell membrane
Maximize the number of metabolic branches
Explanation - FBA optimizes a linear objective, often growth rate (biomass) or ATP yield, subject to stoichiometric constraints.
Correct answer is: Maximize the production of ATP or biomass
Q.3 Which cofactor is most commonly involved in redox reactions within central metabolism?
NAD⁺/NADH
ATP/ADP
cAMP
Ca²⁺
Explanation - NAD⁺/NADH shuttles electrons in many catabolic and anabolic pathways, such as glycolysis and the TCA cycle.
Correct answer is: NAD⁺/NADH
Q.4 The Michaelis‑Menten constant (K_m) reflects:
The maximum velocity of an enzyme-catalyzed reaction
The substrate concentration at which reaction velocity is half‑maximal
The electrical conductance of a membrane channel
The thermodynamic stability of a protein
Explanation - K_m is defined as the substrate concentration at which the reaction proceeds at ½ V_max.
Correct answer is: The substrate concentration at which reaction velocity is half‑maximal
Q.5 In the context of systems biology, a ‘stoichiometric matrix’ (S) has dimensions:
Metabolites × Reactions
Reactions × Enzymes
Genes × Proteins
Cells × Tissues
Explanation - S rows correspond to metabolites, columns to reactions, encoding stoichiometric coefficients.
Correct answer is: Metabolites × Reactions
Q.6 Which of the following is a common method to measure intracellular metabolite concentrations in real time?
Patch‑clamp electrophysiology
Mass spectrometry‑based metabolomics
Western blotting
Electroencephalography (EEG)
Explanation - Metabolomics using LC‑MS or GC‑MS provides quantitative snapshots of intracellular metabolite pools.
Correct answer is: Mass spectrometry‑based metabolomics
Q.7 The term ‘metabolic control analysis’ (MCA) primarily quantifies:
The voltage‑dependent gating of ion channels
The influence of individual enzymes on pathway flux
The genetic inheritance patterns of metabolic disorders
The mechanical forces in cytoskeletal networks
Explanation - MCA defines control coefficients that measure how changes in enzyme activity affect overall pathway flux.
Correct answer is: The influence of individual enzymes on pathway flux
Q.8 In an electrical circuit analogy of metabolism, which component best represents an enzyme that limits flux?
A resistor
A capacitor
An inductor
A voltage source
Explanation - Resistors impede current flow; similarly, a rate‑limiting enzyme restricts metabolic flux.
Correct answer is: A resistor
Q.9 Which pathway converts glucose to pyruvate in the cytosol?
Citric acid cycle
Oxidative phosphorylation
Glycolysis
Pentose phosphate pathway
Explanation - Glycolysis breaks down one glucose molecule into two pyruvate molecules, generating ATP and NADH.
Correct answer is: Glycolysis
Q.10 During oxidative phosphorylation, the chemiosmotic gradient is primarily composed of:
A concentration gradient of glucose
A pH gradient and an electrical potential across the inner mitochondrial membrane
A gradient of calcium ions across the plasma membrane
A gradient of NAD⁺/NADH in the cytosol
Explanation - The proton motive force (Δp) consists of a ΔpH and a membrane potential (ΔΨ) that drives ATP synthesis.
Correct answer is: A pH gradient and an electrical potential across the inner mitochondrial membrane
Q.11 In a metabolic network, a ‘hub metabolite’ is typically:
A metabolite that participates in many reactions
A metabolite that is only produced during starvation
A metabolite that is exclusively found in plant cells
A metabolite that has no known enzyme
Explanation - Hub metabolites like ATP, NAD⁺, and acetyl‑CoA connect multiple pathways, making them central nodes.
Correct answer is: A metabolite that participates in many reactions
Q.12 Which of the following is a key assumption of steady‑state flux balance analysis?
Metabolite concentrations change rapidly over time
All reactions operate at their maximum velocities
The net accumulation of each internal metabolite is zero
Enzyme activities are independent of substrate levels
Explanation - Steady‑state implies dS/dt = 0 for internal metabolites, allowing the system of linear equations S·v = 0.
Correct answer is: The net accumulation of each internal metabolite is zero
Q.13 Which cofactor is primarily involved in transferring one‑carbon units in metabolism?
Coenzyme A (CoA)
FAD
Biotin
Thiamine pyrophosphate (TPP)
Explanation - Biotin acts as a carrier of CO₂ in carboxylation reactions, such as acetyl‑CoA carboxylase.
Correct answer is: Biotin
Q.14 A ‘dead‑end metabolite’ in a reconstructed metabolic model is one that:
Can be produced but not consumed, or vice versa
Is a substrate for every reaction in the network
Has a zero molecular weight
Is only present in eukaryotic cells
Explanation - Dead‑ends indicate gaps or missing reactions that prevent flux through those metabolites.
Correct answer is: Can be produced but not consumed, or vice versa
Q.15 Which of the following best describes the role of an allosteric inhibitor?
It competes with substrate for the active site
It binds to a site other than the active site and decreases enzyme activity
It phosphorylates the enzyme to increase activity
It permanently destroys the enzyme
Explanation - Allosteric inhibitors modulate activity by binding to regulatory sites, causing conformational changes.
Correct answer is: It binds to a site other than the active site and decreases enzyme activity
Q.16 In the context of electrical engineering analogies, the ‘capacitance’ of a metabolite pool would most closely correspond to:
The ability of the pool to store charge (concentration) and release it later
The resistance to flow of electrons through the membrane
The voltage generated by ATP hydrolysis
The inductance of a protein filament
Explanation - Capacitance stores electrical energy; similarly, a metabolite pool can buffer concentration changes.
Correct answer is: The ability of the pool to store charge (concentration) and release it later
Q.17 Which pathway is primarily responsible for generating NADPH for biosynthetic reactions?
Glycolysis
Citric acid cycle
Pentose phosphate pathway
Beta‑oxidation
Explanation - The oxidative branch of the PPP produces NADPH while converting glucose‑6‑phosphate to ribulose‑5‑phosphate.
Correct answer is: Pentose phosphate pathway
Q.18 What does the term ‘flux coupling’ mean in metabolic network analysis?
Two reactions must always operate at the same absolute rate
The flux through one reaction directly determines the flux through another
Reactions share the same enzyme subunit
The electrical potentials of two membranes are identical
Explanation - Flux coupling indicates that if one reaction carries flux, another must also, often due to stoichiometric dependencies.
Correct answer is: The flux through one reaction directly determines the flux through another
Q.19 Which metabolite is the direct donor of the acetyl group for fatty acid synthesis?
Acetyl‑CoA
Propionyl‑CoA
Malonyl‑CoA
Citrate
Explanation - Acetyl‑CoA provides the two‑carbon building block for the initiation of fatty acid chains.
Correct answer is: Acetyl‑CoA
Q.20 In a genome‑scale metabolic model, the term ‘gap‑filling’ refers to:
Adding missing reactions to allow growth in silico
Removing redundant genes from the model
Increasing the resolution of metabolite measurements
Eliminating all dead‑end metabolites
Explanation - Gap‑filling algorithms insert reactions that restore connectivity and enable feasible flux distributions.
Correct answer is: Adding missing reactions to allow growth in silico
Q.21 Which ion gradient powers the bacterial flagellar motor, analogous to an electrical potential in circuits?
Na⁺ gradient
K⁺ gradient
Ca²⁺ gradient
Cl⁻ gradient
Explanation - Many bacteria use a sodium motive force to rotate the flagellum, similar to voltage driving current.
Correct answer is: Na⁺ gradient
Q.22 The term ‘thermodynamic feasibility’ of a reaction in a metabolic model ensures that:
The reaction proceeds in the direction dictated by ΔG°′ < 0 under cellular conditions
The enzyme concentration is above a threshold
The reaction rate is faster than diffusion
The metabolite has a positive charge
Explanation - Thermodynamic constraints prevent flux in directions that would require positive Gibbs free energy under physiological conditions.
Correct answer is: The reaction proceeds in the direction dictated by ΔG°′ < 0 under cellular conditions
Q.23 In the context of metabolic engineering, the ‘knock‑out’ of a gene is performed to:
Increase the electrical conductivity of the cell membrane
Eliminate an enzyme, redirecting flux toward a desired product
Amplify the expression of all downstream genes
Create a new ion channel
Explanation - Gene knock‑outs remove competing pathways, channeling metabolites into engineered routes.
Correct answer is: Eliminate an enzyme, redirecting flux toward a desired product
Q.24 Which metabolic pathway directly links glycolysis and the citric acid cycle?
Pentose phosphate pathway
Beta‑oxidation
Pyruvate dehydrogenase complex
Urea cycle
Explanation - The pyruvate dehydrogenase complex converts pyruvate to acetyl‑CoA, entering the TCA cycle.
Correct answer is: Pyruvate dehydrogenase complex
Q.25 What is the main purpose of using 13C‑labeling experiments in metabolic pathway analysis?
To visualize electrical currents in cells
To track carbon flow through metabolic networks
To increase ATP production
To inhibit specific enzymes
Explanation - 13C‑labeled substrates allow researchers to follow carbon atoms through reactions using mass spectrometry or NMR.
Correct answer is: To track carbon flow through metabolic networks
Q.26 In a circuit analog, the term ‘Kirchhoff’s Current Law’ (KCL) corresponds to which metabolic principle?
Conservation of mass at each metabolite node (S·v = 0)
Conservation of electrical charge across the membrane
Maximum ATP yield per glucose molecule
Enzyme saturation kinetics
Explanation - KCL states that the sum of currents entering a node equals the sum leaving; similarly, metabolite production equals consumption at steady state.
Correct answer is: Conservation of mass at each metabolite node (S·v = 0)
Q.27 Which enzyme catalyzes the rate‑limiting step of the citric acid cycle?
Citrate synthase
Isocitrate dehydrogenase
α‑Ketoglutarate dehydrogenase
Succinate dehydrogenase
Explanation - Isocitrate dehydrogenase is highly regulated and often rate‑limiting in the TCA cycle.
Correct answer is: Isocitrate dehydrogenase
Q.28 In metabolic control analysis, the sum of all flux control coefficients for a given pathway equals:
0
1
Infinity
The number of enzymes in the pathway
Explanation - The summation theorem states that the total control over a pathway flux is distributed among enzymes, summing to unity.
Correct answer is: 1
Q.29 A metabolite that participates in both catabolic and anabolic reactions is known as:
A dead‑end metabolite
A branch point metabolite
A sink metabolite
A co‑factor
Explanation - Branch point metabolites (e.g., pyruvate, oxaloacetate) split flux toward multiple downstream routes.
Correct answer is: A branch point metabolite
Q.30 Which of the following best describes an ‘enzyme isoform’?
An enzyme that can conduct both oxidation and reduction reactions
A different protein that catalyzes the same reaction but with different regulatory properties
An enzyme that only functions at high temperature
An enzyme that is electrically conductive
Explanation - Isoforms arise from gene duplication or alternative splicing, providing regulatory diversity.
Correct answer is: A different protein that catalyzes the same reaction but with different regulatory properties
Q.31 In the context of electrical circuits, which component is analogous to a metabolic ‘feedback inhibition’ loop?
A resistor in series
A capacitor connected to ground
A negative feedback amplifier
An open switch
Explanation - Negative feedback reduces output (flux) when product concentration rises, similar to a feedback amplifier reducing gain.
Correct answer is: A negative feedback amplifier
Q.32 What is the primary purpose of using ‘knock‑down’ (RNAi) instead of a full gene knockout in metabolic studies?
To increase the speed of electron flow
To partially reduce enzyme levels, allowing observation of graded effects
To permanently delete the gene from the genome
To create an artificial electrical field
Explanation - RNAi reduces but does not eliminate expression, enabling study of dose‑dependent metabolic changes.
Correct answer is: To partially reduce enzyme levels, allowing observation of graded effects
Q.33 Which of the following is NOT a typical assumption made in kinetic models of metabolism?
Enzyme concentrations are constant over the simulation period
All reactions follow Michaelis‑Menten kinetics
Metabolite diffusion is instantaneous
Electrical potentials across membranes are ignored
Explanation - Kinetic models often include membrane potentials when relevant; ignoring them is not a standard assumption.
Correct answer is: Electrical potentials across membranes are ignored
Q.34 The Warburg effect describes how cancer cells:
Prefer oxidative phosphorylation over glycolysis even in oxygen-rich conditions
Produce large amounts of ATP via photosynthesis
Rely heavily on aerobic glycolysis, producing lactate despite oxygen availability
Do not use any glucose as a carbon source
Explanation - Cancer cells exhibit high glycolytic rates with lactate production even when oxygen is sufficient.
Correct answer is: Rely heavily on aerobic glycolysis, producing lactate despite oxygen availability
Q.35 In an E. coli metabolic model, the reaction ‘EX_glc(e)’ typically represents:
Glucose export from the cytoplasm to the extracellular space
Glucose uptake from the environment into the cell
Glucose phosphorylation inside the cell
Glucose oxidation in the periplasm
Explanation - ‘EX_’ prefix denotes exchange reactions; ‘EX_glc(e)’ allows glucose to enter the model from the extracellular compartment.
Correct answer is: Glucose uptake from the environment into the cell
Q.36 A ‘stoichiometric bottleneck’ in a metabolic network occurs when:
A reaction has a very high V_max
A metabolite is required by many downstream reactions but is produced in limited quantity
All enzymes are equally expressed
The cell membrane becomes impermeable
Explanation - Limited supply of a key metabolite restricts the overall throughput of the network.
Correct answer is: A metabolite is required by many downstream reactions but is produced in limited quantity
Q.37 In the context of bioelectrical signaling, which ion is most closely linked to the regulation of glycolytic flux in muscle cells?
K⁺
Na⁺
Ca²⁺
Cl⁻
Explanation - Calcium activates phosphofructokinase‑2, modulating glycolysis during muscle contraction.
Correct answer is: Ca²⁺
Q.38 Which computational method combines metabolic network reconstruction with gene expression data to predict active pathways?
Flux Balance Analysis (FBA)
Gene Set Enrichment Analysis (GSEA)
Integrated Metabolic‑Expression Modeling (iMAT)
Molecular Dynamics (MD) simulation
Explanation - iMAT incorporates transcriptomic data into FBA to identify fluxes consistent with gene expression levels.
Correct answer is: Integrated Metabolic‑Expression Modeling (iMAT)
Q.39 The term ‘synthetic lethality’ in metabolic engineering refers to:
Two enzymes that together produce a lethal toxin
A pair of gene deletions that is non‑viable, while each single deletion is viable
A mutation that makes the cell electrically unstable
An overexpression of a transporter leading to cell death
Explanation - Synthetic lethality exploits combinatorial gene knockouts to identify essential metabolic interactions.
Correct answer is: A pair of gene deletions that is non‑viable, while each single deletion is viable
Q.40 In metabolic pathway diagrams, a double‑headed arrow typically indicates:
Irreversible reaction
Reversible reaction
Electrical current flow
Enzyme inhibition
Explanation - Double‑headed arrows denote that the reaction can proceed in both directions depending on conditions.
Correct answer is: Reversible reaction
Q.41 Which of the following metabolites serves as a substrate for both the TCA cycle and fatty acid synthesis?
Acetyl‑CoA
Oxaloacetate
Succinate
Fumarate
Explanation - Acetyl‑CoA enters the TCA cycle for oxidation and is also the building block for fatty acid biosynthesis.
Correct answer is: Acetyl‑CoA
Q.42 When modelling a metabolic network as a graph, nodes usually represent:
Enzymes only
Reactions only
Metabolites
Electrical potentials
Explanation - In bipartite graphs, metabolites are one set of nodes; reactions are the other set.
Correct answer is: Metabolites
Q.43 What is the main advantage of using ‘enzyme‑constrained FBA’ (ecFBA) over conventional FBA?
It eliminates the need for a stoichiometric matrix
It incorporates enzyme abundance and turnover numbers (kcat) to limit fluxes
It replaces linear programming with differential equations
It focuses solely on thermodynamic feasibility
Explanation - ecFBA adds constraints based on enzyme capacity, making predictions more realistic.
Correct answer is: It incorporates enzyme abundance and turnover numbers (kcat) to limit fluxes
Q.44 Which of the following statements about the ‘glyoxylate shunt’ is correct?
It converts acetyl‑CoA directly into glucose
It bypasses the decarboxylation steps of the TCA cycle, allowing net carbon retention
It is the primary source of NADH in mitochondria
It occurs only in human liver cells
Explanation - The glyoxylate cycle enables organisms like bacteria and plants to synthesize carbohydrates from acetyl‑CoA.
Correct answer is: It bypasses the decarboxylation steps of the TCA cycle, allowing net carbon retention
Q.45 In a metabolic network, the term ‘flux variability analysis’ (FVA) is used to:
Determine the range of possible fluxes through each reaction while still achieving the optimal objective
Measure the electrical noise in ion channels
Calculate the exact kinetic parameters of each enzyme
Identify dead‑end metabolites
Explanation - FVA explores solution space around the optimal flux distribution, revealing alternative pathways.
Correct answer is: Determine the range of possible fluxes through each reaction while still achieving the optimal objective
Q.46 Which metabolite acts as an allosteric activator of phosphofructokinase‑1 (PFK‑1) in glycolysis?
ATP
Citrate
Fructose‑2,6‑bisphosphate
Acetyl‑CoA
Explanation - F‑2,6‑BP strongly activates PFK‑1, overriding inhibition by ATP.
Correct answer is: Fructose‑2,6‑bisphosphate
Q.47 Which technique combines metabolite profiling with real‑time electrical measurements to study bioelectrochemical systems?
Patch‑clamp metabolomics
Electrochemical mass spectrometry (EC‑MS)
Fluorescence‑activated cell sorting (FACS)
X‑ray crystallography
Explanation - EC‑MS can monitor metabolites while simultaneously measuring electrochemical signals.
Correct answer is: Electrochemical mass spectrometry (EC‑MS)
Q.48 In the context of metabolic pathway analysis, the term ‘branch‑point analysis’ focuses on:
Identifying metabolites that split flux toward multiple downstream pathways
Measuring the electrical resistance of mitochondrial membranes
Determining the pH of the cytosol
Estimating the number of genes in a genome
Explanation - Branch‑point analysis evaluates how control is distributed at metabolites that feed multiple routes.
Correct answer is: Identifying metabolites that split flux toward multiple downstream pathways
Q.49 Which of the following is an example of a ‘co‑factor recycling’ system in metabolism?
ATP hydrolysis coupled to protein synthesis
NAD⁺ regeneration via lactate dehydrogenase
Glucose transport via GLUT4
DNA replication
Explanation - Lactate dehydrogenase converts pyruvate to lactate while oxidizing NADH back to NAD⁺, maintaining redox balance.
Correct answer is: NAD⁺ regeneration via lactate dehydrogenase
Q.50 A ‘metabolic choke point’ is best described as:
A reaction that consumes a substrate unique to a single pathway
A metabolite that is highly abundant in the cell
An enzyme with a very high turnover number
A membrane channel that blocks ion flow
Explanation - Choke points are attractive drug targets because blocking them disrupts a pathway without alternatives.
Correct answer is: A reaction that consumes a substrate unique to a single pathway
Q.51 Which of the following best represents the role of the enzyme ‘pyruvate carboxylase’ in gluconeogenesis?
Converts pyruvate to oxaloacetate, providing a substrate for glucose synthesis
Degrades glucose into pyruvate
Catalyzes the phosphorylation of ADP
Transfers electrons to the electron transport chain
Explanation - Pyruvate carboxylase adds CO₂ to pyruvate, forming oxaloacetate, a key gluconeogenic intermediate.
Correct answer is: Converts pyruvate to oxaloacetate, providing a substrate for glucose synthesis
Q.52 When converting a kinetic model to an equivalent electrical circuit, the ‘conductance’ of a reaction is analogous to:
The enzyme turnover number (kcat)
The substrate concentration
The Gibbs free energy change
The membrane capacitance
Explanation - Higher kcat enables greater flux, similar to higher conductance allowing more current flow.
Correct answer is: The enzyme turnover number (kcat)
Q.53 Which metabolite is the immediate precursor for the synthesis of the neurotransmitter serotonin?
Tyrosine
Tryptophan
Phenylalanine
Glutamate
Explanation - Tryptophan is hydroxylated and decarboxylated to produce serotonin.
Correct answer is: Tryptophan
Q.54 In a metabolic model, the term ‘exchange reaction’ refers to:
A reaction that converts one metabolite into another within the cell
A reaction that allows metabolites to enter or leave the system boundary
A reversible enzymatic step
A reaction that requires an external electric field
Explanation - Exchange reactions define transport between the intracellular compartment and the extracellular environment.
Correct answer is: A reaction that allows metabolites to enter or leave the system boundary
Q.55 Which pathway is directly responsible for the conversion of acetyl‑CoA to cholesterol in eukaryotes?
Beta‑oxidation
Mevalonate pathway
Urea cycle
Glycogenolysis
Explanation - The mevalonate pathway synthesizes isoprenoids and ultimately cholesterol from acetyl‑CoA.
Correct answer is: Mevalonate pathway
Q.56 In a metabolic flux map, a thick arrow typically indicates:
A high concentration of the metabolite
A high flux (rate) through that reaction
An electrical current
A gene expression level
Explanation - Visual thickness conveys relative magnitude of metabolic fluxes.
Correct answer is: A high flux (rate) through that reaction
Q.57 Which of the following best describes the purpose of ‘thermodynamic flux balance analysis’ (tFBA)?
To incorporate Gibbs free energy constraints into the FBA framework
To model electrical circuits in cells
To predict gene expression levels
To simulate protein folding
Explanation - tFBA adds directionality constraints based on ΔG to improve physiological realism.
Correct answer is: To incorporate Gibbs free energy constraints into the FBA framework
Q.58 The enzyme ‘phosphofructokinase‑2’ primarily regulates glycolysis by:
Producing fructose‑2,6‑bisphosphate, an allosteric activator of PFK‑1
Hydrolyzing ATP directly
Transporting glucose across the membrane
Generating NADPH
Explanation - PFK‑2 synthesizes F‑2,6‑BP, which strongly stimulates PFK‑1, increasing glycolytic flux.
Correct answer is: Producing fructose‑2,6‑bisphosphate, an allosteric activator of PFK‑1
Q.59 Which of the following is a common method to estimate kinetic parameters (Km, Vmax) for enzymes in silico?
Monte Carlo simulation of random walks
Parameter fitting to time‑course metabolomics data
Patch‑clamp recording of ion channels
DNA sequencing
Explanation - Experimental concentration versus time data are fitted to kinetic equations to derive Km and Vmax.
Correct answer is: Parameter fitting to time‑course metabolomics data
Q.60 Which metabolic pathway is essential for the production of ribose‑5‑phosphate for nucleotide biosynthesis?
Glycolysis
Pentose phosphate pathway
Citric acid cycle
Urea cycle
Explanation - The oxidative branch generates ribose‑5‑P, a precursor for nucleotides.
Correct answer is: Pentose phosphate pathway
Q.61 In an electrical‑circuit analogy, what does a ‘voltage source’ represent in a metabolic system?
A high‑energy metabolite that drives reactions (e.g., ATP)
A transport protein
A regulatory gene
A membrane channel
Explanation - ATP provides free energy, analogous to a voltage source that pushes current (flux).
Correct answer is: A high‑energy metabolite that drives reactions (e.g., ATP)
Q.62 Which enzyme catalyzes the conversion of citrate to isocitrate in the TCA cycle?
Aconitase
Citrate synthase
Isocitrate dehydrogenase
Malate dehydrogenase
Explanation - Aconitase performs the dehydration‑hydration steps converting citrate ↔ isocitrate.
Correct answer is: Aconitase
Q.63 The principle of ‘mass balance’ in metabolic modeling ensures that:
Electrical charge is conserved across the membrane
The sum of all reaction rates equals zero
For each metabolite, production equals consumption at steady state
All genes are expressed at equal levels
Explanation - Mass balance is the foundation of stoichiometric models (S·v = 0).
Correct answer is: For each metabolite, production equals consumption at steady state
Q.64 Which metabolite is the primary electron donor for the electron transport chain in mitochondria?
NADH
FADH₂
ATP
CO₂
Explanation - NADH donates electrons to Complex I, initiating the proton pumping process.
Correct answer is: NADH
Q.65 In metabolic pathway analysis, the term ‘isotopomer’ refers to:
A metabolite with a different charge
A molecule that differs only in isotopic composition (e.g., 13C vs 12C)
A protein isoform
An electrical signal pattern
Explanation - Isotopomers are used in labeling experiments to trace carbon flow.
Correct answer is: A molecule that differs only in isotopic composition (e.g., 13C vs 12C)
Q.66 Which of the following best describes the role of the enzyme ‘glutamine synthetase’ in nitrogen metabolism?
Converts glutamate to glutamine, incorporating ammonium
Degrades glutamine to release ammonia
Transfers electrons to the electron transport chain
Synthesizes ATP from ADP
Explanation - Glutamine synthetase catalyzes the ATP‑dependent assimilation of NH₄⁺ into glutamine.
Correct answer is: Converts glutamate to glutamine, incorporating ammonium
Q.67 When performing a ‘knock‑in’ experiment in a metabolic network, the goal is to:
Remove a gene to stop a pathway
Introduce a new gene or enzyme to create a novel reaction
Increase the membrane potential
Decrease the temperature of the culture
Explanation - Knock‑ins add functionality, enabling production of non‑native metabolites.
Correct answer is: Introduce a new gene or enzyme to create a novel reaction
Q.68 Which of the following metabolites is directly involved in the regulation of the TCA cycle via feedback inhibition?
Citrate
Pyruvate
Acetyl‑CoA
Malate
Explanation - High citrate levels inhibit phosphofructokinase and citrate synthase, slowing glycolysis and the TCA cycle.
Correct answer is: Citrate
Q.69 In a metabolic network, the ‘stoichiometric coefficient’ for a substrate in a reaction is:
Always positive
Always negative
Positive for reactants, negative for products
Negative for reactants, positive for products
Explanation - Conventionally, reactants have negative coefficients, products positive, in the stoichiometric matrix.
Correct answer is: Negative for reactants, positive for products
Q.70 Which metabolic pathway provides precursors for the synthesis of heme groups?
Glycolysis
Urea cycle
Porphyrin biosynthesis pathway
Beta‑oxidation
Explanation - The porphyrin pathway synthesizes δ‑aminolevulinic acid, a heme precursor.
Correct answer is: Porphyrin biosynthesis pathway
Q.71 In the context of synthetic biology, a ‘biosensor’ that converts a metabolite concentration into an electrical signal is an example of:
A gene knockout
An enzyme inhibitor
A transducer linking metabolic state to an electronic readout
A membrane channel blocker
Explanation - Biosensors translate biochemical information into measurable electrical outputs.
Correct answer is: A transducer linking metabolic state to an electronic readout
Q.72 Which cofactor is required for the activity of pyruvate dehydrogenase complex?
FAD
Coenzyme A (CoA)
Biotin
Thiamine pyrophosphate (TPP)
Explanation - TPP is essential for the decarboxylation step within the pyruvate dehydrogenase complex.
Correct answer is: Thiamine pyrophosphate (TPP)
Q.73 The ‘Hill coefficient’ in enzyme kinetics provides information about:
The number of substrate molecules bound cooperatively
The enzyme’s thermal stability
The electrical resistance of the enzyme
The pH optimum of the reaction
Explanation - A Hill coefficient >1 indicates positive cooperativity among binding sites.
Correct answer is: The number of substrate molecules bound cooperatively
Q.74 Which of the following statements about the ‘glycogen shunt’ is true?
It is a pathway that converts glucose directly into ATP without intermediates
It allows rapid mobilization of glucose from stored glycogen during energy demand
It synthesizes fatty acids from amino acids
It occurs only in photosynthetic organisms
Explanation - The glycogen shunt refers to glycogen breakdown (glycogenolysis) supplying glucose‑6‑P for glycolysis.
Correct answer is: It allows rapid mobilization of glucose from stored glycogen during energy demand
Q.75 In the analysis of metabolic networks, a ‘dead‑end metabolite’ often indicates:
A measurement error in metabolomics data
A missing reaction or incomplete pathway annotation
An essential metabolite that cannot be synthesized
A metabolite that is only present under anaerobic conditions
Explanation - Dead‑ends suggest gaps in the network that need to be filled for realistic simulations.
Correct answer is: A missing reaction or incomplete pathway annotation
Q.76 Which of the following best describes the relationship between ‘specific activity’ and ‘turnover number (kcat)’ of an enzyme?
Specific activity is kcat divided by the enzyme’s molecular weight
Specific activity is the inverse of kcat
Specific activity and kcat are identical values
Specific activity is unrelated to kcat
Explanation - Specific activity (units/mg) normalizes kcat (s⁻¹) to protein mass.
Correct answer is: Specific activity is kcat divided by the enzyme’s molecular weight
Q.77 In a metabolic model, the term ‘objective function’ most commonly refers to:
The set of differential equations describing enzyme kinetics
A linear combination of fluxes that is maximized or minimized (e.g., biomass)
The electrical voltage across the cell membrane
The temperature at which the reaction occurs
Explanation - The objective function guides the optimization in FBA to predict physiological behavior.
Correct answer is: A linear combination of fluxes that is maximized or minimized (e.g., biomass)
Q.78 Which metabolite functions as a universal energy carrier in cells?
ADP
NAD⁺
ATP
CO₂
Explanation - ATP stores and transfers energy in virtually all cellular processes.
Correct answer is: ATP
Q.79 When modeling metabolism with ordinary differential equations (ODEs), the term ‘stiff system’ refers to:
A system where all reactions have similar rate constants
A system with widely varying timescales, requiring specialized numerical solvers
A system that cannot be solved analytically
A system with no steady state
Explanation - Stiff ODEs contain fast and slow dynamics that challenge standard integrators.
Correct answer is: A system with widely varying timescales, requiring specialized numerical solvers
Q.80 In the context of metabolic pathway analysis, the term ‘crosstalk’ describes:
Electrical interference between ion channels
Interactions where metabolites or enzymes from one pathway affect another pathway
A type of gene mutation
A method for measuring pH
Explanation - Crosstalk integrates distinct metabolic routes, influencing overall cellular behavior.
Correct answer is: Interactions where metabolites or enzymes from one pathway affect another pathway
Q.81 Which of the following enzymes is a key regulator of the entry of acetyl‑CoA into the TCA cycle?
Citrate synthase
Pyruvate kinase
Phosphofructokinase‑1
Glucose‑6‑phosphate isomerase
Explanation - Citrate synthase condenses acetyl‑CoA with oxaloacetate, committing acetyl‑CoA to the TCA cycle.
Correct answer is: Citrate synthase
Q.82 In a metabolic pathway diagram, dashed lines are often used to denote:
Irreversible reactions
Reversible reactions
Regulatory interactions (activation/inhibition)
Electrical connections
Explanation - Dashed or dotted lines commonly indicate regulation rather than substrate flow.
Correct answer is: Regulatory interactions (activation/inhibition)
Q.83 Which analytical technique provides quantitative information on intracellular metabolite concentrations with millisecond time resolution?
Nuclear magnetic resonance (NMR) spectroscopy
Fast Fourier Transform (FFT) analysis
Real‑time fluorescence biosensors
Western blotting
Explanation - Genetically encoded fluorescent sensors can monitor metabolites like ATP or NADH in live cells rapidly.
Correct answer is: Real‑time fluorescence biosensors
Q.84 The primary purpose of adding a ‘biomass equation’ to a genome‑scale metabolic model is to:
Simulate the electrical properties of the cell membrane
Represent the synthesis of all cellular components required for growth
Calculate the total ATP produced per glucose molecule
Determine the pH of the cytosol
Explanation - The biomass equation aggregates precursors needed for cell mass, serving as the objective for growth simulations.
Correct answer is: Represent the synthesis of all cellular components required for growth
Q.85 Which metabolite is a direct precursor for the synthesis of the amino acid serine?
3‑Phosphoglycerate
Acetyl‑CoA
Pyruvate
Oxaloacetate
Explanation - 3‑Phosphoglycerate from glycolysis is diverted into the serine biosynthetic pathway.
Correct answer is: 3‑Phosphoglycerate
Q.86 In metabolic flux analysis using 13C labeling, the term ‘isotopomer fraction’ refers to:
The proportion of a metabolite that is phosphorylated
The percentage of a metabolite pool that contains a specific labeling pattern
The electrical conductance of a membrane channel
The rate of enzyme turnover
Explanation - Isotopomer fractions indicate how 13C atoms are distributed among metabolites, informing pathway activity.
Correct answer is: The percentage of a metabolite pool that contains a specific labeling pattern
Q.87 Which of the following best illustrates the concept of ‘energy coupling’ in metabolism?
Using ATP hydrolysis to drive an otherwise unfavorable reaction
Transporting electrons across the plasma membrane
Binding of a substrate to an enzyme active site
Diffusion of gases through the cell wall
Explanation - Energy coupling links exergonic ATP hydrolysis to endergonic biosynthetic steps.
Correct answer is: Using ATP hydrolysis to drive an otherwise unfavorable reaction
Q.88 In a metabolic model, the ‘GPR’ (gene‑protein‑reaction) association is used to:
Connect gene expression data to reaction flux constraints
Calculate membrane potentials
Determine the pH of the extracellular environment
Measure the electrical resistance of the cell wall
Explanation - GPR rules map which genes encode enzymes that catalyze each reaction, enabling integration of transcriptomics.
Correct answer is: Connect gene expression data to reaction flux constraints
Q.89 Which metabolite is the immediate substrate for the enzyme ‘phosphoglycerate kinase’ in glycolysis?
1,3‑Bisphosphoglycerate
3‑Phosphoglycerate
Fructose‑1,6‑bisphosphate
Glyceraldehyde‑3‑phosphate
Explanation - Phosphoglycerate kinase transfers a phosphate from 1,3‑BPG to ADP, forming ATP and 3‑PG.
Correct answer is: 1,3‑Bisphosphoglycerate
Q.90 The ‘TCA cycle’ is also known as:
Krebs cycle
Calvin cycle
Pentose phosphate pathway
Urea cycle
Explanation - The tricarboxylic acid (TCA) cycle is named after Hans Krebs.
Correct answer is: Krebs cycle
Q.91 In metabolic engineering, the term ‘pathway refactoring’ refers to:
Changing the order of genes in the genome without altering function
Redesigning regulatory elements to optimize expression of a synthetic pathway
Removing all native pathways from the host organism
Increasing the temperature of the culture to speed up reactions
Explanation - Refactoring rebuilds pathways with standardized parts for predictable performance.
Correct answer is: Redesigning regulatory elements to optimize expression of a synthetic pathway
Q.92 Which of the following is NOT a typical output of a flux balance analysis (FBA) simulation?
Predicted growth rate
Distribution of reaction fluxes
Exact enzyme kinetic parameters (Km, Vmax)
Identification of essential genes
Explanation - FBA uses stoichiometry and constraints; it does not compute detailed kinetic parameters.
Correct answer is: Exact enzyme kinetic parameters (Km, Vmax)
Q.93 In the context of systems biology, a ‘module’ usually denotes:
A single metabolite
A set of tightly connected reactions that perform a distinct function
An electrical circuit component
A gene promoter region
Explanation - Modules simplify complex networks by grouping related reactions.
Correct answer is: A set of tightly connected reactions that perform a distinct function
Q.94 Which enzyme catalyzes the formation of urea from ammonia in mammals?
Carbamoyl phosphate synthetase I
Arginase
Ornithine transcarbamylase
Urease
Explanation - CPS‑I initiates the urea cycle by combining ammonia with bicarbonate to form carbamoyl phosphate.
Correct answer is: Carbamoyl phosphate synthetase I
Q.95 The ‘Glyoxylate cycle’ is essential for which biological process in plants?
Photosynthesis
Conversion of fats to sugars during seed germination
Production of chlorophyll
Nitrogen fixation
Explanation - The glyoxylate cycle bypasses decarboxylation steps, allowing net conversion of acetyl‑CoA to carbohydrates.
Correct answer is: Conversion of fats to sugars during seed germination
Q.96 In an electrical‑circuit analogy, the ‘inductance’ of a metabolic reaction could be likened to:
The time delay before a reaction responds to changes in substrate concentration
The maximum flux a reaction can carry
The equilibrium constant of the reaction
The number of enzyme isoforms
Explanation - Inductance resists changes in current; similarly, some reactions have kinetic lags before flux adapts.
Correct answer is: The time delay before a reaction responds to changes in substrate concentration
Q.97 Which of the following metabolites is directly involved in the synthesis of the neurotransmitter acetylcholine?
Choline
Glutamate
Tyrosine
Phenylalanine
Explanation - Acetylcholine is formed by the condensation of choline and acetyl‑CoA.
Correct answer is: Choline
Q.98 When a metabolic pathway is described as ‘linear’, it means that:
All reactions are reversible
Each metabolite is produced by exactly one reaction and consumed by exactly one reaction
The pathway is regulated by a single gene
The pathway does not interact with any other pathways
Explanation - A linear pathway has a single chain of reactions without branches.
Correct answer is: Each metabolite is produced by exactly one reaction and consumed by exactly one reaction
Q.99 The enzyme ‘acetyl‑CoA carboxylase’ is a key regulatory point for:
Fatty acid synthesis
Glycolysis
Amino acid catabolism
DNA replication
Explanation - Acetyl‑CoA carboxylase produces malonyl‑CoA, the committed step in fatty acid biosynthesis.
Correct answer is: Fatty acid synthesis
Q.100 In a metabolic model, a reaction that consumes NADPH and produces NADP⁺ is generally:
An oxidative reaction
A reductive biosynthetic reaction
A transport reaction
A futile cycle
Explanation - NADPH supplies reducing power for biosynthesis; its oxidation indicates a reductive step.
Correct answer is: A reductive biosynthetic reaction
Q.101 Which of the following best explains why mitochondria have a high membrane capacitance compared to the plasma membrane?
Mitochondria have a larger surface area and many internal folds (cristae)
Mitochondria contain more ion channels
Mitochondrial membranes are more permeable to protons
Mitochondria lack a lipid bilayer
Explanation - The extensive inner membrane increases capacitance, akin to a larger plate area in a capacitor.
Correct answer is: Mitochondria have a larger surface area and many internal folds (cristae)
Q.102 The main purpose of adding a ‘thermodynamic feasibility check’ (e.g., using the group contribution method) to a metabolic model is to:
Ensure that all reactions can proceed in the assigned direction under physiological conditions
Increase the speed of the linear programming solver
Identify transcription factors regulating the pathway
Measure intracellular pH
Explanation - Thermodynamic checks prevent unrealistic fluxes that would violate ΔG constraints.
Correct answer is: Ensure that all reactions can proceed in the assigned direction under physiological conditions
Q.103 Which metabolite acts as a substrate for both the TCA cycle and gluconeogenesis, serving as a key ‘gluconeogenic precursor’?
Acetyl‑CoA
Oxaloacetate
Succinate
Fumarate
Explanation - Oxaloacetate can be converted to phosphoenolpyruvate, entering gluconeogenesis.
Correct answer is: Oxaloacetate
Q.104 In a systems‑biology study, integrating transcriptomics with a metabolic model primarily helps to:
Predict the exact concentration of each metabolite
Constrain reaction fluxes based on gene expression levels
Determine the membrane potential of organelles
Measure protein folding rates
Explanation - Gene expression data can be translated into bounds on reaction capacities, refining model predictions.
Correct answer is: Constrain reaction fluxes based on gene expression levels
Q.105 Which of the following is a characteristic feature of a ‘synthetic biology chassis’ organism?
It contains a large number of native metabolic pathways
It is genetically tractable, with minimal native metabolism to reduce interference
It has a highly resistant cell wall
It produces large amounts of ATP spontaneously
Explanation - Chassis strains like E. coli or yeast are engineered to be simple platforms for synthetic pathways.
Correct answer is: It is genetically tractable, with minimal native metabolism to reduce interference
Q.106 Which of the following best describes the function of ‘allosteric regulation’ in metabolic pathways?
Changing the enzyme’s primary amino‑acid sequence
Binding of an effector molecule at a site other than the active site to modify activity
Altering the pH of the cytoplasm
Increasing the temperature of the reaction
Explanation - Allosteric effectors modulate enzyme activity by inducing conformational changes.
Correct answer is: Binding of an effector molecule at a site other than the active site to modify activity
Q.107 In the context of metabolic flux analysis, the term ‘net flux’ refers to:
The difference between forward and reverse reaction rates for a reversible step
The total number of enzymes in a pathway
The electrical current measured across the membrane
The amount of ATP generated per minute
Explanation - Net flux = forward flux – reverse flux; it determines the overall direction of a reversible reaction.
Correct answer is: The difference between forward and reverse reaction rates for a reversible step
Q.108 Which of the following metabolites is a direct substrate for the enzyme ‘glutamate dehydrogenase’?
α‑Ketoglutarate
Oxaloacetate
Pyruvate
Acetyl‑CoA
Explanation - Glutamate dehydrogenase interconverts α‑ketoglutarate and glutamate using NAD(P)H.
Correct answer is: α‑Ketoglutarate
Q.109 Which analytical method is most suitable for measuring the flux through a specific metabolic pathway in vivo?
RNA‑seq
13C metabolic flux analysis (13C‑MFA)
Gel electrophoresis
Chromatin immunoprecipitation (ChIP)
Explanation - 13C‑MFA tracks labeled carbon through pathways, quantifying intracellular fluxes.
Correct answer is: 13C metabolic flux analysis (13C‑MFA)
Q.110 In metabolic network visualization, a ‘bow‑tie’ architecture typically indicates:
A linear sequence of reactions
A central set of core metabolites connecting many input and output pathways
A reversible loop of reactions
An electrical circuit with a ground node
Explanation - Bow‑tie structures have many inputs converging on a core (e.g., central carbon metabolism) that diverges to many outputs.
Correct answer is: A central set of core metabolites connecting many input and output pathways
Q.111 The main energy‑producing step of glycolysis that yields ATP via substrate‑level phosphorylation is:
Hexokinase reaction
Phosphoglycerate kinase reaction
Pyruvate kinase reaction
Glyceraldehyde‑3‑phosphate dehydrogenase reaction
Explanation - Pyruvate kinase transfers a phosphate from phosphoenolpyruvate to ADP, generating ATP.
Correct answer is: Pyruvate kinase reaction
Q.112 Which of the following best describes a ‘metabolite pool’?
The set of all enzymes in a cell
The total concentration of a particular metabolite in a given compartment
The DNA sequence encoding a metabolic enzyme
The electrical charge across a membrane
Explanation - A metabolite pool refers to the amount of a metabolite available for reactions.
Correct answer is: The total concentration of a particular metabolite in a given compartment
Q.113 Which of the following metabolites is a key indicator of cellular redox state?
ATP/ADP ratio
NAD⁺/NADH ratio
Glucose concentration
cAMP level
Explanation - The NAD⁺/NADH ratio reflects the balance between oxidized and reduced forms, indicating redox status.
Correct answer is: NAD⁺/NADH ratio
Q.114 In the context of metabolic network reconstruction, the term ‘gap‑filled reaction’ refers to:
A reaction that is added artificially to resolve dead‑ends or enable growth
A reaction that is removed to simplify the model
A reaction that only occurs under extreme pH
A reaction that does not involve any metabolites
Explanation - Gap‑filling adds missing reactions to create a functional, gap‑free network.
Correct answer is: A reaction that is added artificially to resolve dead‑ends or enable growth
Q.115 Which enzyme catalyzes the conversion of ribulose‑5‑phosphate to ribose‑5‑phosphate in the pentose phosphate pathway?
Ribulose‑5‑phosphate epimerase
Ribose‑5‑phosphate isomerase
Transketolase
Glucose‑6‑phosphate dehydrogenase
Explanation - Ribose‑5‑phosphate isomerase interconverts ribulose‑5‑P and ribose‑5‑P.
Correct answer is: Ribose‑5‑phosphate isomerase
Q.116 In a metabolic model, a ‘binary variable’ is often used to represent:
The concentration of a metabolite
Whether a reaction is active (1) or blocked (0)
The pH of the cytosol
The electrical resistance of a membrane
Explanation - Binary variables enable mixed‑integer programming to include on/off decisions for reactions.
Correct answer is: Whether a reaction is active (1) or blocked (0)
Q.117 Which of the following is a major source of acetyl‑CoA in liver cells under fasting conditions?
Glycolysis
Beta‑oxidation of fatty acids
Pentose phosphate pathway
Urea cycle
Explanation - During fasting, fatty acids are oxidized to generate acetyl‑CoA for the TCA cycle and ketogenesis.
Correct answer is: Beta‑oxidation of fatty acids
Q.118 The term ‘metabolomics’ refers to:
The study of all proteins in a cell
The comprehensive analysis of metabolites in a biological system
The sequencing of the genome
The measurement of electrical activity in neurons
Explanation - Metabolomics captures the global metabolite profile, often using MS or NMR.
Correct answer is: The comprehensive analysis of metabolites in a biological system
Q.119 In an electrical‑circuit representation, the term ‘Ohm’s law’ (V = IR) applied to metabolism would correspond to:
Flux = Conductance × Driving force (e.g., ΔG)
Flux = Concentration × Temperature
Flux = Enzyme concentration × Km
Flux = Membrane potential × Capacitance
Explanation - Analogous to V = IR, metabolic flux can be expressed as conductance (enzyme capacity) times a thermodynamic driving force.
Correct answer is: Flux = Conductance × Driving force (e.g., ΔG)
Q.120 Which of the following metabolites is directly involved in the synthesis of the neurotransmitter dopamine?
Tyrosine
Tryptophan
Phenylalanine
Serine
Explanation - Tyrosine is hydroxylated and decarboxylated to form dopamine.
Correct answer is: Tyrosine
Q.121 In a metabolic flux map, an arrow that points opposite to the direction of the main pathway usually indicates:
A reversible reaction carrying net reverse flux
An error in the diagram
An electrical current
A transcription factor binding site
Explanation - Reverse arrows illustrate that the net direction of a reversible reaction is opposite to the main flow.
Correct answer is: A reversible reaction carrying net reverse flux
Q.122 Which of the following best explains why the TCA cycle is considered amphibolic?
It functions both in the cytosol and mitochondria
It provides both catabolic oxidation of substrates and anabolic precursors for biosynthesis
It alternates between aerobic and anaerobic respiration
It uses both NAD⁺ and NADH
Explanation - The TCA cycle oxidizes acetyl‑CoA for energy and generates intermediates for biosynthetic pathways.
Correct answer is: It provides both catabolic oxidation of substrates and anabolic precursors for biosynthesis
Q.123 In metabolic engineering, the concept of ‘dynamic regulation’ involves:
Keeping enzyme expression constant throughout growth
Altering enzyme levels in response to intracellular or extracellular signals
Removing all feedback inhibition
Increasing temperature to accelerate reactions
Explanation - Dynamic regulation uses sensors and controllers to adjust pathway activity adaptively.
Correct answer is: Altering enzyme levels in response to intracellular or extracellular signals
Q.124 Which of the following is a primary product of the pentose phosphate pathway that is used for nucleotide synthesis?
Ribose‑5‑phosphate
Glyceraldehyde‑3‑phosphate
Acetyl‑CoA
Oxaloacetate
Explanation - Ribose‑5‑P is a precursor for the synthesis of RNA and DNA nucleotides.
Correct answer is: Ribose‑5‑phosphate
Q.125 In a metabolic model, the term ‘exchange reaction’ is used to:
Define reversible steps within the cytosol
Represent the import or export of metabolites across the system boundary
Model enzymatic regulation
Calculate the Gibbs free energy of reactions
Explanation - Exchange reactions allow metabolites to enter or leave the model, mimicking transport.
Correct answer is: Represent the import or export of metabolites across the system boundary
Q.126 Which metabolite is directly involved in the regulation of the enzyme phosphofructokinase‑1 (PFK‑1) by serving as an allosteric inhibitor?
ATP
AMP
Fructose‑2,6‑bisphosphate
Citrate
Explanation - High ATP levels signal sufficient energy and inhibit PFK‑1, slowing glycolysis.
Correct answer is: ATP
Q.127 The primary function of the enzyme ‘malate dehydrogenase’ in the TCA cycle is to:
Convert malate to oxaloacetate while reducing NAD⁺ to NADH
Phosphorylate malate
Decarboxylate malate to produce CO₂
Transport malate across the mitochondrial membrane
Explanation - Malate dehydrogenase catalyzes the reversible oxidation of malate to oxaloacetate, producing NADH.
Correct answer is: Convert malate to oxaloacetate while reducing NAD⁺ to NADH
Q.128 Which of the following best describes the purpose of ‘sensitivity analysis’ in metabolic modeling?
To determine how variations in model parameters affect predicted fluxes or outputs
To measure the electrical conductivity of cell membranes
To sequence the genome of the organism
To visualize metabolic pathways in 3D
Explanation - Sensitivity analysis identifies parameters that have the greatest impact on model predictions.
Correct answer is: To determine how variations in model parameters affect predicted fluxes or outputs
Q.129 In an electrical‑circuit analogy, a ‘voltage divider’ can be used to model:
The distribution of free energy among sequential enzymatic steps
The transport of ions across a membrane
The synthesis of nucleic acids
The replication of DNA
Explanation - A voltage divider splits voltage across resistors; similarly, free energy can be partitioned across consecutive reactions.
Correct answer is: The distribution of free energy among sequential enzymatic steps
Q.130 Which cofactor is essential for the activity of the enzyme ‘pyruvate kinase’?
Mg²⁺
Coenzyme A
NAD⁺
Biotin
Explanation - Mg²⁺ stabilizes ATP and is required for pyruvate kinase catalytic activity.
Correct answer is: Mg²⁺
Q.131 During anaerobic fermentation in yeast, the primary end‑product that regenerates NAD⁺ is:
Ethanol
Lactate
Acetate
Acetyl‑CoA
Explanation - Ethanol fermentation converts pyruvate to ethanol, oxidizing NADH back to NAD⁺.
Correct answer is: Ethanol