How to use biochemistry viva questions
Biochemistry viva questions test more than whether you can recall a pathway. You may need to explain a mechanism, interpret a graph, predict the effect of a mutation, justify a laboratory method or connect a biochemical change to a clinical finding. The difficulty is that the examiner can change direction after any answer.
A reliable preparation method therefore has four parts:
- build answers from first principles rather than memorised paragraphs;
- practise explaining one result, pathway or method aloud;
- learn the small number of equations, assumptions and control steps that support your explanations;
- review the exact point at which your answer became vague or incorrect.
There is no single international biochemistry viva format. Your university, laboratory programme or professional body may set its own duration, topics, permitted materials and assessment criteria, so check the official handbook or website before you plan around a particular format.
For each topic, prepare a short answer at three levels. First give the direct answer. Then explain the mechanism. Finally state how you would test, interpret or apply it. For example, for competitive inhibition:
- Direct answer: a competitive inhibitor competes with substrate for the active site.
- Mechanism: increasing substrate concentration can overcome the inhibition, so apparent Km increases while Vmax is unchanged in the ideal model.
- Application: inspect the Lineweaver–Burk plot cautiously, consider the assay conditions, and distinguish the pattern from mixed or irreversible inhibition.
That structure prevents two common problems: giving a definition without understanding it, or speaking for several minutes before answering the question.
Set up an examiner-led practice system
Start with a revision board made from your own lecture slides, laboratory notes, practical reports and marked assignments. Divide it by the types of answer you may need to give, not only by textbook chapter. Useful sections include enzyme kinetics, metabolism, molecular biology, analytical methods, laboratory quality and clinical interpretation.
Each section should contain the facts an examiner could reasonably ask you to use. Include units, assumptions, control reactions, rate-limiting steps and common sources of error. Do not copy every page of notes. A viva board should show relationships such as substrate, enzyme, product, cellular location, regulation and clinical consequence.
When you practise, answer the opening question in under a minute. Then allow follow-up questions to expose whether you can reason beyond the prepared definition. A good session alternates between recall, interpretation and defence of a method.
A biochemistry viva examiner persona should make those demands visible before you begin:
MySummaries uses an examiner strip like this to keep the practice focused on the type of explanation being assessed.
The purpose is not to imitate a particular person. It is to remind you that a fluent answer still needs correct chemistry, an explicit chain of reasoning and an interpretation that matches the evidence.
Build stations from the board
Create stations that force you to move between knowledge and use. A useful set might include:
- explaining an enzyme assay and its controls;
- interpreting a kinetic graph or spectrophotometric result;
- tracing a metabolic response to a change in hormones or energy status;
- explaining a mutation or regulatory defect;
- evaluating an unexpected laboratory result.
Write an opening question for each station, then prepare likely follow-ups. Do not script every sentence. Instead, write the indispensable points and the errors you must avoid. For an enzyme assay, the indispensable points might be linear initial-rate measurement, a blank, appropriate controls, substrate concentration, temperature and pH control, replicates, and the distinction between enzyme activity and enzyme concentration.
The station table below shows how a set can be organised. The percentages represent practice performance, not an official examination result.
Notice that the opening questions are broad enough to produce follow-ups. The examiner can ask what changes on a graph, why a control is needed, where a pathway occurs, or which result would make you question the assay. Those follow-ups are where superficial learning is exposed.
Station 1: enzyme kinetics and inhibition
Before answering, identify what the question is asking you to distinguish. It is not enough to define the inhibitor. You need to link the inhibition model to observable kinetic parameters and acknowledge the limits of the model.
Examiner
Explain how you would distinguish competitive from non-competitive inhibition using an enzyme assay.
You correctly stated that competitive inhibition raises apparent Km while leaving Vmax unchanged in the ideal case.
ImproveState that pure non-competitive inhibition lowers Vmax without changing Km, then qualify that real mixed inhibition can change both parameters.
You proposed measuring initial rates over several substrate concentrations with and without inhibitor.
ImproveName technical replicates and explain why substrate, enzyme, pH and temperature must be controlled.
You recognised that the pattern should be judged from fitted kinetic data rather than one reaction tube.
ImproveExplain what result would support each model and avoid treating a Lineweaver–Burk plot as automatically definitive.
The answer followed a sensible definition, experiment and interpretation order.
ImproveGive the direct distinction in the first sentence before discussing the graph.
A strong answerI would measure initial reaction rates across a range of substrate concentrations, both without inhibitor and at a defined inhibitor concentration, while keeping enzyme, pH, temperature and ionic conditions constant. In the ideal competitive model, the apparent Km increases but Vmax is unchanged because sufficiently high substrate can overcome competition for the active site. In pure non-competitive inhibition, Vmax decreases while Km is unchanged, although real inhibitors may show mixed behaviour and alter both values. I would fit the data using an appropriate nonlinear model, include blanks and replicates, and use the residuals and confidence intervals rather than relying only on a linearised plot.
The strong answer does three things that a memorised definition does not. It specifies initial rates, it links the mechanism to the kinetic parameters, and it avoids overclaiming what a single graph proves. If asked a follow-up about irreversible inhibition, explain that loss of active enzyme reduces the available catalytic capacity and cannot be reversed simply by adding more substrate.
Station 2: an LDH assay and laboratory controls
This station tests whether you can interpret a signal without assuming that every change is the analyte of interest. State what the instrument measures, what reaction produces the signal, and how you know the signal is specific and within the assay's working range.
Examiner
Your absorbance at 340 nm rises over time. What does that tell you, and what controls do you require before reporting activity?
You correctly linked absorbance at 340 nm to NADH and stated that LDH direction depends on the reaction mixture.
ImproveState explicitly whether NADH is being consumed or produced in the selected direction before assigning a rise or fall to LDH activity.
You included a reagent blank, a sample blank, positive control and replicate measurements.
ImproveAdd the need to confirm linearity with time and proportionality to sample volume or enzyme concentration.
You recognised that turbidity, haemolysis and readings outside the linear range can distort the result.
ImproveExplain that a rising trace alone does not establish specificity for LDH without suitable reaction controls.
You separated the optical signal from the conclusion about enzyme activity.
ImproveEnd with the reporting condition: activity is reported only after quality checks pass.
A strong answerAt 340 nm I am monitoring NADH, not LDH directly. If the reaction is arranged so that NADH is produced, an increasing absorbance may reflect the coupled LDH reaction; if NADH is consumed, the direction will be reversed. I would include a reagent blank, a sample blank where appropriate, a known control, technical replicates and a check that the absorbance change is linear over the measurement interval. I would also check for haemolysis, turbidity, instrument saturation and a result outside the validated range before reporting activity, because an optical change alone does not prove a specific LDH measurement.
A useful habit is to say the direction of the reaction explicitly. LDH catalyses the reversible interconversion of pyruvate and lactate with NADH and NAD⁺. Whether absorbance at 340 nm rises or falls depends on which direction the assay has been designed to measure. This is a small detail, but it demonstrates control of the chemistry rather than recall of an isolated wavelength.
Station 3: insulin and post-meal metabolism
For pathway questions, do not list every enzyme. Start with the physiological state, then describe the signal, the key transport or regulatory step, and the fate of the substrate. Finish by linking the pathway to a measurable consequence.
Examiner
Explain how insulin promotes glucose storage after a carbohydrate-containing meal.
You correctly described insulin signalling, GLUT4 movement in skeletal muscle and adipose tissue, glycogenesis and inhibition of hepatic glucose production.
ImproveDistinguish insulin-dependent GLUT4 uptake in muscle and adipose tissue from hepatic glucose handling, where GLUT2 is the major transporter.
You linked the receptor tyrosine kinase to downstream signalling and storage pathways.
ImproveInclude activation of glycogen synthase through reduced inhibitory phosphorylation and mention suppression of glycogen breakdown.
You connected carbohydrate storage with reduced circulating glucose and altered lipid metabolism.
ImproveExplain that excess carbohydrate can support fatty-acid synthesis in the fed state, rather than implying all glucose becomes glycogen.
The answer moved logically from hormone release to tissue-specific effects.
ImproveName the tissue at each step so that a general statement about glucose uptake does not become misleading.
A strong answerAfter a carbohydrate-containing meal, increased blood glucose stimulates pancreatic beta cells to release insulin. Insulin binds its receptor tyrosine kinase and activates signalling that promotes GLUT4 translocation to the surface of skeletal muscle and adipose cells, increasing glucose uptake. In liver and muscle it promotes glycogen synthesis by favouring glycogen synthase activity and suppresses glycogen breakdown and hepatic gluconeogenesis. In adipose tissue it supports triglyceride storage by increasing glucose availability and reducing lipolysis. The overall effect is movement of glucose into storage and use, with reduced hepatic glucose output.
This answer is stronger when tissue differences are kept accurate. Saying that insulin simply makes every cell take up glucose is too broad. A viva examiner may immediately ask about the liver, brain or red blood cells. Prepare a short answer for each: the liver uses GLUT2 and changes its metabolic flux, while some tissues have insulin-independent glucose uptake mechanisms.
Improve the spoken answer, not just the notes
After each station, review the recording for three specific faults: a wrong biochemical statement, a missing link in the reasoning, or a sentence that sounds confident but says nothing testable. Mark only the phrases that cost marks. This gives you a smaller and more useful correction task than rewriting the whole answer.
A transcript review might identify the point at which a safety or interpretation statement became too vague:
I would check the controls and then report the result. The assay should be fine if the absorbance changes steadily. I would also repeat it if needed. I would compare it with the expected control range before deciding.
The assay should be fine if the absorbance changes steadily
A linear trace supports a usable measurement interval but does not establish specificity, accuracy or acceptable control performance.
Say: I would confirm linearity, blank correction, control recovery, replicate agreement and the validated measurement range before reporting activity.Practise replacing vague verbs such as check, assess and confirm with the actual action. Say what you would measure, compare or calculate. If you mention a control, state what error it detects. If you mention a graph, state which feature changes and what that means chemically.
One concise debrief can reinforce the behaviour you want to repeat:
You separated the NADH signal from the conclusion about LDH activity; next time, name the reaction direction before interpreting whether absorbance should rise or fall.
A weekly way to practise biochemistry viva questions
Use one station for each practice session rather than trying to cover an entire subject aloud. A 30-minute session can be structured as follows:
- Five minutes: recall the board's core facts without looking.
- Three minutes: answer the opening question under a timer.
- Ten minutes: answer follow-ups on mechanism, controls and interpretation.
- Seven minutes: listen back and identify one knowledge gap and one communication problem.
- Five minutes: repeat the answer using the correction.
On the next day, begin with the corrected answer before opening a new station. At the end of the week, mix stations so that you do not rely on chapter order. Include at least one question requiring a calculation or graph interpretation. For example, be ready to state that Beer–Lambert behaviour is commonly expressed as A = εcl, define absorbance, molar absorptivity, path length and concentration, and explain why dilution may be needed when the sample is outside the method's linear range.
Keep an error log with four headings: fact, mechanism, interpretation and delivery. A fact error needs retrieval practice. A mechanism error needs a pathway redrawn from cause to consequence. An interpretation error needs more varied data examples. A delivery problem needs a shorter opening sentence or a clearer tissue, reagent or control named aloud.
How MySummaries helps
MySummaries can turn your biochemistry notes into a revision board, then use that board to generate oral stations, record your answers and mark them against criteria such as biochemical accuracy, mechanistic reasoning, data interpretation and clear communication. It can also turn repeated weak points into flashcards for spaced practice, so the correction from a viva session returns in a later session rather than disappearing into your notes.
Start with your own material at portal.mysummaries.app, then build stations around the pathways, methods and practical work your course actually covers.