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Free practice questions, preparation advice, and expert insights for Biochemistry interviews at Imperial College London.
Real Biochemistry interview questions in the style Imperial College London asks. Try answering each one aloud before you reveal the hint.
An enzyme obeys Michaelis-Menten kinetics with a Vmax of 60 micromol/min and a Km of 4 mM. What is the initial reaction rate when the substrate concentration is 4 mM, and what does that value tell you physically?
Problem-Solving & Quantitative
Hint
At [S] = Km the rate is exactly Vmax/2 by definition; a candidate should recover 30 micromol/min and explain that Km is the substrate concentration giving half-maximal velocity, not a binding constant per se.
A weak acid has a pKa of 6.1. You need a buffer at pH 7.4, the physiological blood pH. What ratio of conjugate base to acid does this require, and why is bicarbonate an unusual choice of buffer given this figure?
Problem-Solving & Quantitative
Hint
Apply Henderson-Hasselbalch to get a ratio near 20:1, then note that the system works because CO2 is volatile and removed by the lungs, so it is an open buffer rather than a closed one.
In a Lineweaver-Burk (double-reciprocal) plot, a competitive inhibitor is added. Sketch how the line moves and derive from the equation why the y-intercept is unchanged but the x-intercept shifts.
Problem-Solving & Quantitative
Hint
1/v vs 1/[S] gives a straight line with y-intercept 1/Vmax and slope Km/Vmax; a competitive inhibitor raises apparent Km but leaves Vmax fixed, so the slope steepens while the y-intercept holds.
The complete oxidation of one molecule of glucose is often quoted as yielding around 30-32 ATP. Walk through where the major contributions come from, and explain why the textbook number was revised down from 38.
Problem-Solving & Quantitative
Hint
Account for substrate-level phosphorylation in glycolysis and the TCA cycle, then oxidative phosphorylation from NADH and FADH2; the revision reflects non-integer P/O ratios and the cost of shuttling cytosolic NADH into the mitochondrion.
Enzymes lower the activation energy of a reaction but do not change its equilibrium position. Reconcile these two statements using the free-energy profile of a catalysed versus uncatalysed reaction.
Conceptual Reasoning
Hint
The candidate should distinguish thermodynamics from kinetics: an enzyme stabilises the transition state, lowering the barrier in both directions equally, so it speeds attainment of equilibrium without altering the relative free energies of substrate and product.
Structured interviews that combine technical problem-solving with motivation and personal statement discussion.
Imperial interviews vary by department. Engineering and Computing tend to be technical with problem-solving elements. Medicine uses a Multiple Mini Interview (MMI) format with several short stations. Most interviews last 15-30 minutes and may include a presentation or group exercise.
Interview Invitation
Late Nov
Arrival to Interview
Early Dec
Technical Question
Mid Dec
Decision
Early Jan
Interview Invitation
Late Nov
Arrival to Interview
Early Dec
Technical Question
Mid Dec
Decision
Early Jan
A protein's primary sequence is said to determine its three-dimensional fold, yet many proteins require chaperones to fold correctly in the cell. Is Anfinsen's principle wrong, and how would you reconcile this?
midHint
Strong answers separate thermodynamic determination (the native state is the global free-energy minimum encoded by the sequence) from the kinetic problem of reaching it inside a crowded cell, where chaperones prevent aggregation and misfolding traps.
The genetic code is described as degenerate. Explain what this means, and argue whether that degeneracy is a flaw or a feature under mutational pressure.
midHint
Degeneracy means multiple codons specify one amino acid, largely through the third-position wobble; the candidate should argue it buffers against point mutations, as many become synonymous or conservative, reducing the phenotypic impact of error.
Two enzymes catalyse the same reaction but one has a much higher kcat/Km ratio. What does this ratio represent, and why is an enzyme approaching a kcat/Km near 10^8 to 10^9 said to be 'catalytically perfect'?
hardHint
kcat/Km is the specificity constant and the effective second-order rate constant at low [S]; perfection means the rate is limited by the diffusion of substrate to the active site rather than by the chemistry, so no further catalytic improvement helps.
Your statement mentions an interest in enzyme kinetics. Pick one enzyme you have read about and explain a piece of experimental evidence that revealed how it works.
entryHint
Look for a candidate who can name a specific enzyme and describe a real observation, for example how kinetic or structural data distinguished a mechanism, rather than reciting a textbook definition of Km and Vmax.
You write that biochemistry appeals to you because it is quantitative. Imperial expects readiness for data-analysis and even programming work. Where in your reading or practical experience did numerical reasoning change a conclusion you had drawn?
midHint
The candidate should give a concrete instance where a calculation, graph or statistical point overturned an intuition, showing genuine comfort with quantitative bioscience rather than a stated preference for it.
You cite reading on epigenetics or gene regulation. What was one claim in that reading you were not fully convinced by, and how would you go about testing it?
midHint
This probes critical reading over enthusiasm; a strong answer isolates a specific, testable claim, identifies what evidence would confirm or refute it, and proposes a plausible experimental or observational approach.
Beyond the laboratory, molecular bioscience feeds into medicine, biotechnology and industry. Which application of biochemistry made you want to study it at depth, and what open scientific question within it still interests you?
hardHint
Reward candidates who connect a real application to an unresolved question and can articulate what remains uncertain, demonstrating that their interest is evidence-led and forward-looking rather than a career slogan.
0.10 mol of a diprotic acid is dissolved in 1 litre of water and fully neutralised by NaOH. How many moles of NaOH are required, and how would the titration curve differ from that of a monoprotic acid of the same concentration?
entryHint
0.20 mol of base is needed; the candidate should describe two equivalence points and, if the pKa values are well separated, two distinct buffer regions on the curve.
A stretch of DNA is 30% adenine by base composition. Using Chargaff's rules, work out the percentage of each of the other three bases, and state one assumption you have made.
entryHint
A = T = 30% and G = C = 20%; the key assumption is that the DNA is double-stranded, since Chargaff's base-pairing equalities do not hold for single-stranded genomes.
The equilibrium N2 + 3H2 gives 2NH3 is exothermic. Predict how yield of ammonia responds to increased temperature and increased pressure, and explain the industrial compromise that follows.
midHint
Le Chatelier's principle predicts higher pressure favours ammonia (fewer gas moles) while higher temperature lowers yield but raises rate; the Haber process compromises at moderate temperature with a catalyst to reach acceptable yield in acceptable time.
A first-order reaction has a rate constant of 0.10 per minute. How long until three-quarters of the reactant has been consumed, and why can you answer this without knowing the starting concentration?
hardHint
Three-quarters consumed is two half-lives; with a first-order half-life of ln2/k about 6.9 minutes, the answer is roughly 13.9 minutes, and independence from starting concentration is the defining property of first-order kinetics.
Why is it that a fever of a few degrees can be dangerous, when we happily cook and eat proteins at far higher temperatures? Reason from the molecular level.
midHint
The candidate should connect the narrow thermal stability window of the proteome, cooperative denaturation and loss of enzyme function near body temperature, distinguishing reversible conformational effects from the irreversible denaturation of cooking.
If you could add a completely new amino acid to the standard set of twenty, what chemical property would you give its side chain and what new capability might that unlock for proteins?
hardHint
There is no single right answer; assess how the candidate reasons about side-chain chemistry, for example novel catalytic groups, metal coordination or photo-reactivity, and how they anticipate consequences for folding and the translation machinery.
A drug works beautifully in a test tube against a purified enzyme but fails completely in a living cell. Suggest as many distinct reasons as you can for that gap.
hardHint
Look for breadth: membrane permeability, off-target binding, metabolism or efflux, compartmentalisation, competing endogenous substrate concentrations, and redundancy in the pathway; the point is systematic hypothesis generation.
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A quick refresher on enzyme-substrate interaction, active sites and inhibition.
Useful for consolidating carbohydrates, lipids, proteins and nucleic acids before deeper biochemistry.
Introduces rate reasoning relevant to biochemistry and ESAT-style problem solving.
Good starting point for revising energetics and metabolism.
Helps applicants explore breadth in bioscience careers and subfields.
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Further Reading
by Bruce Alberts et al.
A visual, accessible bridge into molecular machines and cellular scale.
by Nessa Carey
Useful for applicants interested in gene regulation, chromatin and biomedical applications.
by Lewis Wolpert
A readable introduction to cell biology and disease mechanisms for personal-statement exploration.
by UAT-UK
Primary source for ESAT guide, specimen materials and relevant archived papers.
by UAT-UK
Official reference for ESAT dates, format, scoring and registration guidance.
by Biochemical Society
Useful topic enrichment and glossary support for molecular bioscience.
by Biochemical Society
Shows the breadth of molecular bioscience pathways beyond a laboratory-only view.
by Imperial College London Careers Service
Imperial-specific career exploration page for Life Sciences students.