100+ Free MCAT Bio/Biochem Practice Questions

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A researcher is investigating protein quaternary structure. He finds that hemoglobin (a tetramer of α₂β₂ subunits) exhibits cooperative oxygen binding (sigmoidal O₂-dissociation curve), while myoglobin (a monomer) shows a hyperbolic curve. What is the molecular basis of hemoglobin's cooperativity?

Hemoglobin cooperativity occurs because the four subunits share a single heme group that must be serially loaded

Hemoglobin has 4× more heme groups than myoglobin, giving it intrinsically higher affinity for O₂

Myoglobin has lower affinity for O₂ than hemoglobin in systemic capillaries, so it cannot accept O₂ from hemoglobin

Oxygen binding to one subunit of hemoglobin causes a T-state → R-state conformational transition that increases O₂ affinity of the remaining unbound subunits (positive cooperativity via subunit communication)

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2026 Statistics

Key Facts: MCAT Bio/Biochem Exam

59 questions / 95 minutes

Section Format

AAMC MCAT Essentials 2026

118–132

Section Score Range

AAMC

65% introductory biology, 25% biochemistry, 10% chemistry

Content Discipline Weights

AAMC Biological and Biochemical Foundations Overview

~125

National Median Score (50th percentile, 2025–2026)

AAMC Percentile Ranks

$355 total MCAT exam fee (2026)

Registration Cost

AAMC MCAT Essentials for Testing Year 2026

10 passages (4–6 questions each) + 15 discrete questions

Question Structure

AAMC

The MCAT Biological and Biochemical Foundations section is one of four scored sections on the Medical College Admission Test, administered by the AAMC. It consists of 59 questions answered in 95 minutes (10 passage-based sets of 4–6 questions plus 15 discrete items). The section is scored on a scale of 118–132, with the national median near 125 and the 90th percentile at 129. Content is weighted approximately 65% introductory biology, 25% first-semester biochemistry, 5% general chemistry, and 5% organic chemistry. The 2026 exam format is unchanged from the 2015 redesign, per AAMC MCAT Essentials (October 2025).

Sample MCAT Bio/Biochem Practice Questions

Try these sample questions to test your MCAT Bio/Biochem exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1An amino acid has a pKa of 2.2 for its alpha-carboxyl group and a pKa of 9.2 for its alpha-amino group. At physiological pH (7.4), what is the predominant ionic form of this amino acid?

A.Fully protonated (cationic) form with +1 charge

B.Zwitterion with net zero charge

C.Anionic form with –1 charge on carboxylate

D.Fully deprotonated (anionic) form with –2 charge

Explanation: At pH 7.4, which is between the two pKa values (2.2 and 9.2), both the carboxyl group (pKa 2.2) is deprotonated (–COO⁻) and the amino group (pKa 9.2) is protonated (–NH₃⁺), resulting in a zwitterion with net zero charge. The isoelectric point (pI) ≈ (2.2 + 9.2)/2 = 5.7, and pH 7.4 is above the pI, so the net charge is near zero but still predominantly zwitterionic.

2Which of the following amino acids is most likely to be found in the interior of a globular protein in aqueous solution?

A.Lysine

B.Aspartate

C.Leucine

D.Serine

Explanation: Leucine is a nonpolar, hydrophobic amino acid with an isobutyl side chain. In aqueous environments, globular proteins fold so that hydrophobic residues are buried in the interior to minimize unfavorable interactions with water (the hydrophobic effect). Charged or polar residues are typically found on the surface.

3Passage: A researcher studies a mutant enzyme that converts substrate S to product P. Kinetic data collected at varying [S] with fixed enzyme concentration are shown below: [S] (mM) | Initial velocity (µM/min) 0.5 | 15 1.0 | 25 2.0 | 37 5.0 | 48 10.0 | 53 The researcher estimates Vmax ≈ 60 µM/min from a Lineweaver-Burk plot. What is the approximate Km of this enzyme?

A.0.5 mM

B.2.0 mM

C.5.0 mM

D.10.0 mM

Explanation: Km is the substrate concentration at half-maximal velocity. With Vmax ≈ 60 µM/min, half-maximal velocity = 30 µM/min. From the data, initial velocity ≈ 30 µM/min occurs between [S] = 1.0 mM (v=25) and [S] = 2.0 mM (v=37), approximately at [S] ≈ 2.0 mM. This is the best match among the choices.

4Passage (continued from above): A competitive inhibitor (I) is added at a fixed concentration. Which change in kinetic parameters is expected?

A.Vmax decreases; Km stays the same

B.Vmax stays the same; apparent Km increases

C.Both Vmax and Km increase

D.Both Vmax and Km decrease

Explanation: Competitive inhibitors compete with substrate for the active site. They increase the apparent Km (more substrate is required to reach half-maximal velocity) but do not affect Vmax because excess substrate can outcompete the inhibitor. On a Lineweaver-Burk plot, lines with and without inhibitor intersect on the y-axis (same Vmax) but have different x-intercepts (different Km).

5During glycolysis, glucose is converted to two molecules of pyruvate. Which of the following correctly describes the net energy yield per glucose in glycolysis under aerobic conditions?

A.Net gain of 1 ATP and 1 NADH

B.Net gain of 2 ATP and 2 NADH

C.Net gain of 4 ATP and 2 NADH

D.Net gain of 2 ATP and 2 FADH₂

Explanation: Glycolysis produces 4 ATP by substrate-level phosphorylation but consumes 2 ATP in the investment phase (hexokinase and phosphofructokinase steps), giving a net of 2 ATP per glucose. Two NADH are produced from glyceraldehyde-3-phosphate dehydrogenase. No FADH₂ is generated in glycolysis.

6A patient with Type I (insulin-dependent) diabetes develops ketoacidosis. Which metabolic pathway is primarily responsible for the accumulation of ketone bodies in this condition?

A.Gluconeogenesis in the liver

B.Beta-oxidation and ketogenesis in the liver

C.Glycogenolysis in skeletal muscle

D.Fatty acid synthesis in adipose tissue

Explanation: In the absence of insulin, lipolysis in adipose tissue releases free fatty acids that flood the liver. Hepatic beta-oxidation generates excess acetyl-CoA that cannot enter the TCA cycle (oxaloacetate is depleted by gluconeogenesis), so it is channeled into ketogenesis, producing acetoacetate, beta-hydroxybutyrate, and acetone. These accumulate, lowering blood pH.

7Which of the following best describes the role of ubiquitin in eukaryotic protein degradation?

A.Ubiquitin directly cleaves peptide bonds in misfolded proteins

B.Ubiquitin tags proteins for recognition and degradation by the 26S proteasome

C.Ubiquitin acts as a chaperone that refolds denatured proteins

D.Ubiquitin transports proteins to lysosomes for degradation

Explanation: Ubiquitin is a small 76-amino-acid protein that is covalently attached to lysine residues of target proteins by a cascade of E1, E2, and E3 enzymes. Polyubiquitinated proteins are recognized and unfolded by the 19S regulatory caps of the 26S proteasome, then degraded by the proteolytic 20S core. This is the primary pathway for regulated cytoplasmic protein degradation.

8In the citric acid cycle (TCA cycle), one turn around the cycle starting from acetyl-CoA produces which of the following?

A.1 ATP, 3 NADH, 1 FADH₂, and 2 CO₂

B.2 ATP, 2 NADH, 2 FADH₂, and 2 CO₂

C.1 GTP, 3 NADH, 1 FADH₂, and 2 CO₂

D.1 GTP, 2 NADH, 2 FADH₂, and 2 CO₂

Explanation: One turn of the TCA cycle (per acetyl-CoA) yields: 3 NADH (isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, malate dehydrogenase), 1 FADH₂ (succinate dehydrogenase), 1 GTP/ATP (succinyl-CoA synthetase), and 2 CO₂ (released at isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase). In most tissues, GTP is produced directly; it is energetically equivalent to ATP.

9Passage: A biochemist studies the electron transport chain (ETC) in isolated mitochondria. She adds rotenone, a specific inhibitor of Complex I (NADH dehydrogenase). Which of the following results would be expected? She measures oxygen consumption, NADH levels, and the proton gradient (ΔpH across the inner mitochondrial membrane).

A.Oxygen consumption increases; NADH levels decrease; proton gradient increases

B.Oxygen consumption decreases; NADH levels increase; proton gradient decreases

C.Oxygen consumption is unchanged; NADH levels decrease; proton gradient is unchanged

D.Oxygen consumption increases; NADH levels increase; proton gradient decreases

Explanation: Rotenone blocks Complex I, preventing NADH from donating electrons to ubiquinone. Electrons cannot flow through the chain to Complex IV (cytochrome c oxidase), so O₂ consumption decreases. NADH cannot be oxidized and accumulates. Fewer protons are pumped across the inner membrane by Complexes I, III, and IV, so the proton gradient (ΔpH/ΔΨ) decreases, and ATP synthase slows.

10Passage (continued): The biochemist then adds succinate (a TCA cycle intermediate) to the inhibited preparation. What effect would this have on ATP synthesis?

A.No change, because all electron flow is blocked by rotenone

B.Partial restoration of ATP synthesis, because succinate donates electrons to Complex II (FADH₂ pathway), bypassing Complex I

C.Full restoration of ATP synthesis, because succinate regenerates NADH

D.ATP synthesis decreases further, because succinate is an inhibitor of Complex III

Explanation: Succinate is oxidized by Complex II (succinate dehydrogenase) to fumarate, reducing FAD to FADH₂. The electrons are then passed to ubiquinone (CoQ) and flow through Complexes III and IV to oxygen, bypassing Complex I entirely. This partially restores the proton gradient and ATP synthesis, although the contribution is smaller than if Complex I were functional (because only Complexes III and IV pump protons, not I).

About the MCAT Bio/Biochem Exam

The Biological and Biochemical Foundations of Living Systems (Bio/Biochem) is the third section of the MCAT. It tests 59 multiple-choice questions (44 passage-based across 10 passages + 15 discrete questions) in 95 minutes. Disciplines tested: 65% introductory biology, 25% first-semester biochemistry, 5% general chemistry, and 5% organic chemistry. The section is organized around three foundational concepts and assesses scientific inquiry and reasoning skills.

Questions

59 scored questions

Time Limit

95 minutes

Passing Score

Scored 118–132; national median ~125; competitive applicants aim for 128+

Exam Fee

$355 (full MCAT exam, 2026) (Association of American Medical Colleges (AAMC))

MCAT Bio/Biochem Exam Content Outline

65%

Introductory Biology

Cell biology (organelles, membrane transport, cell cycle, mitosis/meiosis), molecular biology (DNA replication, transcription, RNA processing, translation, gene regulation), genetics (Mendelian inheritance, Hardy-Weinberg, mutations, epigenetics), microbiology (bacteria, viruses), and organ system physiology (nervous, endocrine, circulatory, immune, digestive, renal, reproductive, musculoskeletal)

25%

Biochemistry

Amino acids and protein structure (primary through quaternary), enzyme kinetics (Michaelis-Menten, Km, Vmax, inhibition types), carbohydrates (glycolysis, TCA cycle, pentose phosphate pathway, glycogen metabolism), lipids (fatty acid synthesis and oxidation, membrane structure, lipid classes), nucleic acids (DNA/RNA structure, base pairing), and major metabolic pathways and their regulation

General Chemistry

Acid-base equilibria and buffer systems (Henderson-Hasselbalch), electrochemistry as applied to membrane potentials and redox reactions in the electron transport chain

Organic Chemistry

Functional group reactivity relevant to biochemical mechanisms: nucleophilicity, carbonyl chemistry (thioesters, amide bonds), lipid structure, and reactions in metabolic pathways (oxidation, reduction, carboxylation)

How to Pass the MCAT Bio/Biochem Exam

What You Need to Know

Passing score: Scored 118–132; national median ~125; competitive applicants aim for 128+
Exam length: 59 questions
Time limit: 95 minutes
Exam fee: $355 (full MCAT exam, 2026)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

MCAT Bio/Biochem Study Tips from Top Performers

1Master metabolic pathways systematically: learn glycolysis → pyruvate dehydrogenase → TCA cycle → ETC/oxidative phosphorylation as one connected story, tracking ATP, NADH, and FADH₂ yields and all regulatory steps.

2For enzyme kinetics, practice drawing and interpreting Michaelis-Menten curves and Lineweaver-Burk plots. Know how competitive, noncompetitive, uncompetitive, and mixed inhibition change Km and Vmax — this is very high-yield.

3Use the AAMC content outline to build a checklist; check off every topic in Foundational Concepts 1–3. Prioritize organ system physiology (especially renal, cardiovascular, and endocrine) because these are heavily tested in passage-based questions.

4Practice with at least 3 full-length AAMC practice exams under timed conditions, then review every question — even ones you got right. The AAMC Section Banks and Question Packs are closest to the real exam's difficulty and passage style.

5For genetics questions, practice pedigree analysis and remember that meiotic recombination, independent assortment, and Hardy-Weinberg equilibrium all appear regularly. Know X-linked, autosomal dominant, autosomal recessive, and mitochondrial inheritance patterns cold.

Frequently Asked Questions

How many questions and how much time are in the MCAT Bio/Biochem section?

The Biological and Biochemical Foundations of Living Systems section has 59 questions (44 passage-based + 15 discrete) and a time limit of 95 minutes, giving approximately 1 minute 36 seconds per question.

What score range is used for this section and what is a competitive score?

Each MCAT section is scored from 118 to 132. The national median for Bio/Biochem is approximately 125. Scores of 129–132 are highly competitive for top medical school programs.

What percentage of the MCAT Bio/Biochem section is biochemistry vs. biology?

According to the AAMC, approximately 25% of questions come from first-semester biochemistry and 65% from introductory biology. The remaining 10% is split between general chemistry (~5%) and organic chemistry (~5%).

What are the three foundational concepts tested in this section?

Foundational Concept 1 (55%): Structure and function of biological molecules (proteins, carbohydrates, lipids, nucleic acids, enzymes). Foundational Concept 2 (20%): Transmission of genetic information from gene to protein. Foundational Concept 3 (25%): Processes of cell and organ system function and their integration.

How are MCAT scores calculated — is it graded on a curve?

MCAT scores are not curved. The raw score (number correct) is converted to a scaled score (118–132) through an equating process that accounts for minor differences in difficulty across test forms. A score of ~125 corresponds to the 50th percentile for this section.

What is the MCAT exam fee in 2026?

The total MCAT registration fee is $355 for 2026 (increased from $335 in 2025), as published in the AAMC MCAT Essentials for Testing Year 2026. The AAMC Fee Assistance Program offers reduced fees for eligible applicants.