MCAT Practice Test 2026

About the MCAT exam

The Medical College Admission Test (MCAT) is a medical examination administered in USA. It is designed to assess candidates' knowledge and proficiency across 4 key subject areas including Biology & Biochemistry, Chemical & Physical Foundations, Psychological & Social Foundations, Critical Analysis & Reasoning. This exam is widely recognized as an essential benchmark for medical students and practitioners.

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8 free MCAT practice questions (2026)

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1. A novel drug is developed to treat Alzheimer's disease by targeting acetylcholinesterase. In vitro assays demonstrate that the drug binds only to the enzyme-substrate complex, decreasing both the apparent Vmax and the apparent Km by the exact same factor. What type of inhibition is this drug exhibiting?

   • Competitive inhibition
   • Noncompetitive inhibition
   • Uncompetitive inhibition
   • Mixed inhibition
   Show answer & explanation

   Answer: C. Uncompetitive inhibition

   Uncompetitive inhibitors bind exclusively to the enzyme-substrate (ES) complex. This shifts the binding equilibrium toward the ES complex, apparently increasing the enzyme's affinity for the substrate (lowering the apparent Km). Because some enzyme is locked in the inactive ESI complex, the maximum velocity of the reaction is also reduced (lowering the apparent Vmax). Both parameters decrease by the same ratio, maintaining a constant Vmax/Km slope on a Lineweaver-Burk plot.

   Topic: Biology & Biochemistry · medium

2. Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, is caused by inherited mutations in genes such as MSH2 and MLH1. These genes are primarily involved in which of the following cellular processes?

   • Nucleotide excision repair
   • Base excision repair
   • Mismatch repair
   • Non-homologous end joining
   Show answer & explanation

   Answer: C. Mismatch repair

   MSH2 and MLH1 code for essential proteins in the mismatch repair (MMR) pathway. This pathway is responsible for identifying and correcting erroneous base-pairing insertions or deletions that occur during DNA replication and manage to escape proofreading by DNA polymerase.

   Topic: Biology & Biochemistry · easy

3. I-cell disease is a rare lysosomal storage disorder caused by a deficiency in the enzyme N-acetylglucosaminamine-1-phosphotransferase. Consequently, essential lysosomal enzymes are constitutively secreted into the extracellular space rather than being directed to lysosomes. Which of the following post-translational modifications is missing from these enzymes?

   • Mannose-6-phosphate
   • GPI anchor
   • KDEL sequence
   • Ubiquitin tag
   Show answer & explanation

   Answer: A. Mannose-6-phosphate

   Proteins targeted for the lysosome undergo glycosylation in the rough endoplasmic reticulum and are subsequently tagged with mannose-6-phosphate (M6P) in the Golgi apparatus. The enzyme N-acetylglucosaminamine-1-phosphotransferase is required to create this M6P tag. Without it, lysosomes lack their functional enzymes, which are instead default-secreted out of the cell.

   Topic: Biology & Biochemistry · medium

4. During periods of fasting, glucagon stimulates a signaling cascade that decreases glycolytic flux and increases gluconeogenesis in the liver. Which of the following changes in regulatory enzymes occurs in response to elevated glucagon levels?

   • Phosphorylation of PFK-2/FBPase-2, leading to decreased levels of fructose 2,6-bisphosphate
   • Dephosphorylation of PFK-2/FBPase-2, leading to increased levels of fructose 2,6-bisphosphate
   • Activation of pyruvate kinase by fructose 1,6-bisphosphate
   • Inhibition of fructose 1,6-bisphosphatase by ATP
   Show answer & explanation

   Answer: A. Phosphorylation of PFK-2/FBPase-2, leading to decreased levels of fructose 2,6-bisphosphate

   Glucagon binds to G protein-coupled receptors, activating protein kinase A (PKA). PKA phosphorylates the bifunctional enzyme PFK-2/FBPase-2. In the liver, phosphorylation activates the FBPase-2 domain while inactivating the PFK-2 domain. This causes the breakdown of fructose 2,6-bisphosphate (F2,6BP). Since F2,6BP is a potent allosteric activator of phosphofructokinase-1 (PFK-1) and inhibitor of fructose 1,6-bisphosphatase, its reduction slows glycolysis and promotes gluconeogenesis.

   Topic: Biology & Biochemistry · hard

5. The loop of Henle is critical for establishing the medullary osmotic gradient. A patient is treated with a loop diuretic, such as furosemide, which inhibits the Na+/K+/2Cl- cotransporter in the thick ascending limb. What is the expected effect of this drug on urine concentration and blood volume?

   • Increased urine concentration, increased blood volume
   • Decreased urine concentration, decreased blood volume
   • Decreased urine concentration, increased blood volume
   • Increased urine concentration, decreased blood volume
   Show answer & explanation

   Answer: B. Decreased urine concentration, decreased blood volume

   By inhibiting the Na+/K+/2Cl- cotransporter in the thick ascending limb, loop diuretics prevent the active accumulation of salts in the renal medulla. This disrupts the osmotic gradient needed for water reabsorption in the collecting duct. Consequently, less water is reabsorbed, resulting in dilute (decreased concentration) urine and a substantial decrease in intravascular blood volume.

   Topic: Biology & Biochemistry · medium

6. In an isolated population of rabbits, a recessive genetic allele causes white fur, while the dominant allele causes brown fur. If the frequency of white rabbits (homozygous recessive) in this population is 9%, what is the expected frequency of heterozygous brown rabbits, assuming the population is in Hardy-Weinberg equilibrium?

   • 9%
   • 21%
   • 42%
   • 49%
   Show answer & explanation

   Answer: C. 42%

   According to the Hardy-Weinberg equation: p^2 + 2pq + q^2 = 1. The frequency of the homozygous recessive phenotype (q^2) is 0.09. Therefore, the frequency of the recessive allele (q) is sqrt(0.09) = 0.3. Since p + q = 1, the frequency of the dominant allele (p) must be 1 - 0.3 = 0.7. The frequency of heterozygotes (2pq) is calculated as 2 * (0.7) * (0.3) = 0.42, or 42%.

   Topic: Biology & Biochemistry · easy

7. Tetrodotoxin (TTX), a highly potent neurotoxin isolated from pufferfish, selectively blocks voltage-gated sodium channels in excitable membranes. Which of the following phases of the neuronal action potential would be most directly and immediately blocked by TTX?

   • Depolarization
   • Repolarization
   • Hyperpolarization
   • Resting membrane potential restoration
   Show answer & explanation

   Answer: A. Depolarization

   Depolarization of a neuron is driven by the rapid influx of sodium ions (Na+) through voltage-gated sodium channels. If these channels are blocked by TTX, Na+ cannot enter the cell, preventing depolarization and halting the generation of action potentials.

   Topic: Biology & Biochemistry · easy

8. The conversion of glucose to glucose-6-phosphate by hexokinase has a standard free energy change (delta G0') of +13.8 kJ/mol. When this reaction is coupled to the hydrolysis of ATP (delta G0' = -30.5 kJ/mol), what is the overall standard free energy change of the coupled reaction, and is it thermodynamically favorable?

   • +44.3 kJ/mol, unfavorable
   • -16.7 kJ/mol, favorable
   • -16.7 kJ/mol, unfavorable
   • +16.7 kJ/mol, favorable
   Show answer & explanation

   Answer: B. -16.7 kJ/mol, favorable

   To find the overall standard free energy change of coupled reactions, their individual delta G0' values are added together: +13.8 kJ/mol + (-30.5 kJ/mol) = -16.7 kJ/mol. A negative delta G0' indicates that the overall reaction is exergonic and thermodynamically favorable.

   Topic: Biology & Biochemistry · medium

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MCAT Exam Subjects

Available practice subjects: Biology & Biochemistry, Chemical & Physical Foundations, Psychological & Social Foundations, Critical Analysis & Reasoning. Select a subject for focused preparation. Coverage is not a guarantee of the complete official syllabus.

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