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Question-First Step 1 Biochemistry Practice

USMLE Step 1 Biochemistry Practice Questions

Explore the major biochemistry topics covered in BiochemStep's mechanism-focused Step 1 question bank, then start with the free 20-question preview.

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Topics represented in the 20-question free preview

Amatoxin inhibition of RNA polymerase II Aspirin and irreversible cyclooxygenase inhibition Classic PKU (phenylalanine hydroxylase deficiency)Cyanide poisoning ELISA antigen or antibody detection Familial hypercholesterolemia Folate deficiency G6PD deficiency Lesch-Nyhan syndrome (HGPRT deficiency)MCAD deficiency PCR primer amplification / target DNA detection Refeeding syndrome diagnosis Tay-Sachs disease (hexosaminidase A)Vitamin B12 deficiency Von Gierke disease Xeroderma pigmentosum due to defective nucleotide excision repair

Coverage by foundational science area

Major topic areas covered

Amino Acid Metabolism

Bilirubin Metabolism Disorders

Crigler-Najjar syndromeFull bank topic Gilbert syndromeFull bank topic

Branched-Chain Amino Acid Metabolism Disorders

Maple syrup urine disease (BCKD complex deficiency)Full bank topic

Homocystinuria

Homocystinuria (cystathionine beta-synthase deficiency)Full bank topic

Phenylalanine Metabolism Disorders

BH4 deficiency hyperphenylalaninemiaFull bank topic Classic PKU (phenylalanine hydroxylase deficiency)Free question Maternal PKU teratogenicityFull bank topic

Porphyrin and Heme Synthesis Disorders

Acute intermittent porphyria (PBG deaminase)Full bank topic Lead poisoningFull bank topic Porphyria cutanea tardaFull bank topic

Tryptophan and Niacin Metabolism

Pellagra / niacin depletion from carcinoidFull bank topic

Tyrosine Metabolism Disorders

AlkaptonuriaFull bank topic Tyrosinemia type IFull bank topic

Urea Cycle Disorders

CPS I deficiencyFull bank topic OTC deficiencyFull bank topic

Carbohydrate Metabolism

Alcohol Metabolism

Alcohol-induced hypoglycemiaFull bank topic Alcohol-induced hypoglycemia / NADH shiftFull bank topic Ethylene glycol poisoning / aldehyde dehydrogenase / glycolic acid / metabolic acidosisFull bank topic Methanol / ethylene glycol poisoningFull bank topic Methanol poisoningFull bank topic

Disaccharide Metabolism

Primary lactase deficiencyFull bank topic

Fructose Metabolism

Essential fructosuria (Fructokinase deficiency)Full bank topic Fructose-1,6-bisphosphatase deficiencyFull bank topic Hereditary fructose intolerance (Aldolase B)Full bank topic

Galactose Metabolism

Classic galactosemia (GALT deficiency)Full bank topic Galactokinase deficiencyFull bank topic

Glucokinase / MODY

Glucokinase MODY (GCK-MODY, MODY2)Full bank topic

Glucose Metabolism Regulation

Fructose-2,6-bisphosphate regulation of glycolysis and gluconeogenesisFull bank topic Glycogen synthase and glycogen phosphorylase regulationFull bank topic

Glycation and Glucose Monitoring

HbA1c formation mechanismFull bank topic

Glycogen Storage Diseases

Andersen diseaseFull bank topic Cori diseaseFull bank topic McArdle diseaseFull bank topic Pompe diseaseFull bank topic Von Gierke diseaseFree question

Glycolysis Disorders

Pyruvate kinase deficiencyFull bank topic

Mitochondrial Toxicity and Oxidative Phosphorylation

2,4-Dinitrophenol (DNP) toxicityFull bank topic Carbon monoxide poisoningFull bank topic

PDH Complex

Pyruvate dehydrogenase complex deficiencyFull bank topic Pyruvate dehydrogenase deficiencyFull bank topic

Pentose Phosphate Pathway

G6PD deficiencyFree question

Polyol Pathway

Diabetic cataract via polyol pathwayFull bank topic

Thiamine-Dependent Metabolism

Transketolase and thiamine deficiency (Wernicke encephalopathy)Full bank topic

Enzyme Kinetics

Competitive vs noncompetitive vs uncompetitive

Lead poisoning and ALAD inhibitionFull bank topic Organophosphate poisoning and acetylcholinesterase inhibitionFull bank topic

Digestive enzyme activation

Enteropeptidase deficiency and zymogen activationFull bank topic

Enzyme Deficiencies and Pharmacologic Toxicity

Pseudocholinesterase deficiency and succinylcholine paralysisFull bank topic

Enzyme Kinetics

Competitive inhibition / alcohol dehydrogenase / ethylene glycol poisoningFull bank topic Competitive inhibition / Lineweaver-Burk plot / HMG-CoA reductaseFull bank topic

Glucokinase / MODY

GCK-MODYFull bank topic

Suicide inhibitors / irreversible inhibition

Aspirin and irreversible cyclooxygenase inhibitionFree question Organophosphate poisoning and irreversible acetylcholinesterase inhibitionFull bank topic

Genetics & Cell Biology

Amino Acid Transport Disorders

Hartnup disease mechanism (tryptophan malabsorption and NAD+ deficiency)Full bank topic

Apoptosis and Cell Signaling

Bcl-2 / Fas / caspasesFull bank topic

Cell Signaling

G proteins: Gs / Gi / Gq + cholera / pertussis toxinsFull bank topic NO / cGMP / PDE5 inhibitorsFull bank topic Receptor tyrosine kinases / JAK-STATFull bank topic

Chromosomal Aneuploidies

Trisomy 18 / meiotic nondisjunction / quad screenFull bank topic Trisomy 21 / meiotic nondisjunction / quad screenFull bank topic

Collagen and Connective Tissue Disorders

Osteogenesis imperfecta due to abnormal type I collagenFull bank topic

Cystic Fibrosis and CFTR

CFTR F508del misfolding mechanismFull bank topic CFTR mutation classes and meconium ileusFull bank topic CFTR potentiator mechanism (ivacaftor)Full bank topic

DNA Repair Disorders

Fanconi anemia / interstrand crosslink repair / bone marrow failureFull bank topic

Embryology and Developmental Patterning

HOX genes / anterior-posterior patterning / hand-foot-genital syndromeFull bank topic

Genomic Imprinting Disorders

Angelman syndrome genetic mechanismFull bank topic Prader-Willi syndrome diagnosisFull bank topic

Inheritance Patterns

Autosomal dominant inheritance / Variable expressivityFull bank topic

Lysosomal Storage Diseases

I-cell disease (Mucolipidosis II)Full bank topic I-cell disease due to defective mannose-6-phosphate generationFull bank topic

Membrane Transport and Ion Gradients

Membrane transporters and electrochemical gradientsFull bank topic

Mitochondrial Genetics

MELAS and mitochondrial inheritanceFull bank topic MERRF and heteroplasmyFull bank topic

Mucopolysaccharidoses

Hunter syndrome due to iduronate-2-sulfatase deficiencyFull bank topic Hurler syndrome due to alpha-L-iduronidase deficiencyFull bank topic

Oncogene and Tumor Suppressor Signaling

Bilateral renal masses with retinal hemangioblastomas and secondary polycythemiaFull bank topic Hamartomatous syndrome with germline loss of a growth factor signaling brakeFull bank topic Marked leukocytosis with splenomegaly and basophiliaFull bank topic Pancreatic mass with a gain-of-function mutation in a signaling proteinFull bank topic Targeted antibody therapy for breast carcinoma with receptor overexpressionFull bank topic Targeted oral therapy for marked leukocytosis with splenomegalyFull bank topic

Population Genetics

Autosomal recessive inheritance / carrier risk / Hardy-Weinberg equilibriumFull bank topic

Sphingolipidoses

Fabry disease due to alpha-galactosidase A deficiencyFull bank topic Gaucher disease (glucocerebrosidase)Full bank topic Krabbe disease due to galactocerebrosidase deficiencyFull bank topic Niemann-Pick type A (sphingomyelinase)Full bank topic Tay-Sachs disease (hexosaminidase A)Free question

Trinucleotide Repeat Disorders

Fragile X syndrome (CGG repeat expansion in FMR1)Full bank topic Fragile X syndrome molecular mechanism (FMR1 hypermethylation)Full bank topic

Tumor Suppressor and Oncogene Mechanisms

Familial adenomatous polyposis / APC / beta-catenin / Wnt signalingFull bank topic Li-Fraumeni syndrome / TP53 / p53 / p21Full bank topic Retinoblastoma / Rb / two-hit hypothesisFull bank topic

Immunology & Hematologic Mechanisms

Antigen Processing and Presentation

MHC I antigen processingFull bank topic MHC II antigen processingFull bank topic

B-Cell Development and Primary Immunodeficiency

B-cell maturation defect with panhypogammaglobulinemiaFull bank topic Infant with absent B cells and panhypogammaglobulinemiaFull bank topic

Coagulation Regulation and Hypercoagulability

Familial venous thromboembolism in a young woman on oral contraceptivesFull bank topic Paradoxical skin necrosis after initiation of oral anticoagulationFull bank topic Post-flight proximal deep venous thrombosis with an inherited coagulation regulatory defectFull bank topic

Complement Deficiencies and Bacterial Defense

Functional consequence of recurrent meningitis immune defectFull bank topic Young adult with recurrent meningitis due to gram-negative diplococciFull bank topic

Complement Regulation and Angioedema

Acute nonhistaminergic laryngeal edema treated with targeted therapyFull bank topic Recurrent nonpruritic angioedema unresponsive to antihistaminesFull bank topic

Cytokine Signaling and Granuloma Maintenance

Cavitary pulmonary infection after biologic immunosuppressionFull bank topic

Hemoglobin and Red Cell Disorders

Hereditary spherocytosis / erythrocyte membrane / vertical linkage defectFull bank topic Methemoglobinemia / ferric heme iron / benzocaineFull bank topic Paroxysmal nocturnal hemoglobinuria / GPI anchor / complement hemolysisFull bank topic Sickle cell disease / HbS / beta-globin mutation / dactylitisFull bank topic Sickle cell disease due to a missense mutation in beta-globinFull bank topic

Lymphocyte Development and Antibody Diversification

Hyper-IgM phenotype with preserved B-cell numbersFull bank topic Hyper-IgM syndrome with opportunistic infectionsFull bank topic

Lymphocyte Development and Receptor Diversity

T-negative, B-negative, NK-positive severe combined immunodeficiencyFull bank topic

Oxidative Burst and Phagocyte Function

Chronic granulomatous disease / NADPH oxidaseFull bank topic

Phagocyte Adhesion and Innate Immune Defects

Delayed umbilical cord separation with infections without pusFull bank topic

Phagocyte Function and Vesicle Trafficking Disorders

Partial albinism with recurrent infections and giant neutrophil granulesFull bank topic

T-Cell Activation and Immunosuppressive Signaling

Post-transplant immunosuppression and T-cell activationFull bank topic Post-transplant immunosuppression and T-cell proliferationFull bank topic

T-Cell Regulation and Immune Checkpoints

Tumor immune evasion through inhibitory T-cell signalingFull bank topic

Integrated Metabolism & Physiology

Acid-Base Physiology

Metabolic alkalosisFull bank topic

Digestive Enzyme Activation

Trypsinogen activation / enteropeptidase / acute pancreatitisFull bank topic

Drug Metabolism and Toxic Metabolites

Delayed hepatocellular injury after analgesic overdoseFull bank topic Early treatment after analgesic overdoseFull bank topic Reduced hormonal contraceptive effectiveness after antimicrobial therapyFull bank topic

Fasting, Starvation, and Gluconeogenesis

Brain fuel source in prolonged starvationFull bank topic Cori cycle and alanine cycleFull bank topic Protein sparing in prolonged fasting (urea nitrogen excretion)Full bank topic Pyruvate carboxylase activation in fastingFull bank topic

Hemoglobin Biochemistry and Oxygen Transport

Fetal hemoglobin and decreased 2,3-BPG bindingFull bank topic Hemoglobin allostery and 2,3-BPGFull bank topic

Iron Metabolism and Hepcidin Regulation

Hereditary hemochromatosis / hepcidin / ferroportin / HFE mutationFull bank topic

Membrane Transport and Ion Gradients

Digoxin / Na+K+ ATPase / digoxin toxicityFull bank topic

Oxidative Phosphorylation

ATP synthase / chemiosmotic theoryFull bank topic Cyanide poisoningFree question ETC complex inhibitors (rotenone, antimycin, oligomycin)Full bank topic

Renal Acid-Base Physiology

Distal RTA type 1 / H+ ATPase / alpha-intercalated cellsFull bank topic

Signal Transduction and Cytoskeletal Pharmacology

Acute crystal-associated monoarthritis treated with anti-inflammatory therapyFull bank topic

Signal Transduction and Receptor Biology

Concentrated urine after treatment for postoperative water diuresisFull bank topic Drug-induced hyperglycemia through altered hepatic gene expressionFull bank topic Hormonal replacement restoring metabolic rate in hypothyroidismFull bank topic Polyuria and hypernatremia during chronic mood-stabilizer therapyFull bank topic Postprandial glucose uptake in insulin-sensitive tissuesFull bank topic

Lab Techniques

Cytogenetic Techniques

FISH for microdeletion or translocation detectionFull bank topic Karyotype vs chromosomal microarrayFull bank topic

Gene Editing Techniques

CRISPR-Cas9 gene disruption / guide RNA targetingFull bank topic

Immunologic and Protein Detection Techniques

ELISA antigen or antibody detectionFree question Flow cytometry / CD4 T-cell quantification / HIVFull bank topic IHC / immunofluorescence tissue-based detectionFull bank topic Immunoblot / Western blot protein-specific antibody detectionFull bank topic

Molecular Diagnostic Techniques

Next-generation sequencing / variant detectionFull bank topic PCR primer amplification / target DNA detectionFree question RT-qPCR / gene expression quantification / beta-thalassemiaFull bank topic Sanger sequencing and chain terminationFull bank topic

Separation Techniques

Gel electrophoresis / fragment-size separationFull bank topic

Lipid Metabolism

Cholesterol Synthesis and LDL Receptor Regulation

HMG-CoA reductase inhibition (statins)Full bank topic PCSK9 inhibitor mechanism (alirocumab)Full bank topic Statin mechanism of LDL loweringFull bank topic

Diabetic Ketoacidosis

Diabetic ketoacidosisFull bank topic Hormone-sensitive lipase and DKAFull bank topic

Fatty Acid Oxidation and Transport

Beta-oxidation steps / odd-chain FAFull bank topic Carnitine palmitoyltransferase I deficiencyFull bank topic CPT-I deficiency acylcarnitine profileFull bank topic MCAD deficiencyFree question

Fatty Acid Synthesis and Regulation

Acetyl-CoA carboxylase dephosphorylation in fed stateFull bank topic Malonyl-CoA and CPT-I regulation in DKAFull bank topic Malonyl-CoA inhibition of CPT-IFull bank topic

Ketone Body Metabolism

Ketone body utilization and SCOT deficiency in hepatocytesFull bank topic

Lipoprotein Metabolism Disorders

Abetalipoproteinemia diagnosisFull bank topic Familial chylomicronemia syndrome diagnosisFull bank topic Familial chylomicronemia syndrome mechanismFull bank topic Familial hypercholesterolemiaFree question Familial hypercholesterolemia diagnosisFull bank topic Familial hypercholesterolemia mechanismFull bank topic

Metabolic Pathway Pharmacology

LDL reduction after cholesterol-lowering therapyFull bank topic

Odd-Chain Fatty Acid and Propionate Metabolism

Methylmalonic acidemiaFull bank topic

Molecular Biology

Chromatin and Epigenetic Regulation

Azacitidine mechanism in myelodysplastic syndromeFull bank topic Histone H1 and higher-order chromatin compactionFull bank topic

Collagen and Connective Tissue Disorders

Marfan syndrome due to defective fibrillin-1Full bank topic Scurvy due to defective collagen hydroxylation in the rough endoplasmic reticulumFull bank topic Vascular Ehlers-Danlos syndrome due to defective type III collagenFull bank topic

DNA Repair and Cancer Therapy

BRCA-associated ovarian carcinoma treated with PARP inhibitionFull bank topic Lynch syndrome due to defective DNA mismatch repairFull bank topic Xeroderma pigmentosum due to defective nucleotide excision repairFree question

Protein Folding and Misfolding

Alpha-1 antitrypsin deficiency causing emphysema and liver diseaseFull bank topic

Protein Structure and Misfolding

Prion protein conformational change in Creutzfeldt-Jakob diseaseFull bank topic

RNA Processing and Gene Expression

Beta-thalassemia / splice-site mutation / pre-mRNA splicingFull bank topic Nusinersen mechanism in spinal muscular atrophyFull bank topic

Telomeres and Genome Maintenance

Telomerase activity in malignant cellsFull bank topic

Toxin-Mediated Inhibition of Protein Synthesis

Shiga toxin inhibition of the 60S ribosomal subunitFull bank topic

Transcription and Translation

Amatoxin inhibition of RNA polymerase IIFree question

Trinucleotide Repeat Disorders

Huntington disease due to CAG repeat expansion in the coding regionFull bank topic

Nucleotide Metabolism

Antiviral Nucleotide Analogs

Acyclovir activation in herpes simplex virus infectionFull bank topic

Aspirin Pharmacology

Aspirin irreversible COX inhibition and prolonged antiplatelet effectFull bank topic Aspirin-exacerbated respiratory disease (AERD) pathophysiologyFull bank topic

Drug Metabolism and Pharmacogenomics

Severe myelosuppression after thiopurine immunosuppressionFull bank topic

Folate Antimetabolites and Rescue

Folate pathway inhibition (methotrexate / trimethoprim / pyrimethamine)Full bank topic Methotrexate toxicityFull bank topic Methotrexate with leucovorin rescue in osteosarcomaFull bank topic

Microbial Diagnostic Reasoning

Tularemia diagnosis (Francisella tularensis)Full bank topic

Purine Metabolism

Adenosine deaminase deficiency SCIDFull bank topic Allopurinol inhibition of xanthine oxidase in tumor lysis prophylaxisFull bank topic De novo purine synthesis: PRPP amidotransferase regulationFull bank topic Lesch-Nyhan syndrome (HGPRT deficiency)Free question Rasburicase mechanism in tumor lysis syndromeFull bank topic Tumor lysis syndromeFull bank topic

Pyrimidine and Purine Antimetabolites

5-fluorouracil (5-FU)Full bank topic Colon cancer chemotherapy and pyrimidine metabolismFull bank topic Methotrexate (MTX)Full bank topic Thymidylate synthase inhibition (5-FU / capecitabine)Full bank topic

Pyrimidine Metabolism

Hereditary orotic aciduria (UMP synthase deficiency)Full bank topic

Translation and Protein Synthesis Inhibitors

Aminoglycoside mechanism in pseudomonal sepsis with acute tubular necrosisFull bank topic Chloramphenicol mechanism and hematologic toxicityFull bank topic Diphtheria toxin mechanism (EF-2 ADP-ribosylation)Full bank topic

Vitamin B6 and Heme Synthesis

Isoniazid-induced B6 deficiency: ALAS reaction (succinyl-CoA + glycine)Full bank topic Isoniazid-induced pyridoxine deficiency and sideroblastic anemiaFull bank topic

Nutrition

Niacin Deficiency

Pellagra diagnosis (niacin deficiency)Full bank topic

Protein-Energy Malnutrition

Kwashiorkor diagnosisFull bank topic Kwashiorkor vs marasmusFull bank topic

Refeeding Syndrome

Refeeding syndromeFull bank topic Refeeding syndrome diagnosisFree question

Thiamine Deficiency

Wernicke encephalopathy mechanism (alpha-KG dehydrogenase)Full bank topic Wet beriberi diagnosis (thiamine deficiency)Full bank topic

Trace Elements and Micronutrients

Acrodermatitis enteropathica (ZIP4 / SLC39A4)Full bank topic Zinc deficiency / zinc finger transcription factors / TPNFull bank topic

Vitamins & Cofactors

Copper Metabolism Disorders

Menkes disease (ATP7A)Full bank topic Wilson disease and ATP7B-mediated biliary copper excretionFull bank topic

Fat-Soluble Vitamins

Acquired vitamin K deficiency in adults (gamma-carboxylation)Full bank topic Nutritional rickets laboratory pattern (vitamin D deficiency)Full bank topic Vitamin A deficiency / excessFull bank topic Vitamin D deficiency (rickets/osteomalacia)Full bank topic Vitamin E deficiency in cystic fibrosis (antioxidant function)Full bank topic Vitamin K deficiency bleeding of infancy (gamma-carboxylation)Full bank topic

Iron Metabolism and Hepcidin Regulation

Hepcidin-mediated ferroportin internalization in anemia of inflammationFull bank topic

Water-Soluble Vitamins

Biotin deficiencyFull bank topic Folate deficiencyFree question Folate deficiency lab pattern (elevated homocysteine, normal MMA)Full bank topic Folate deficiency mechanism (dTMP synthesis impairment)Full bank topic Folate trap mechanism in vitamin B12 deficiency (methionine synthase)Full bank topic Scurvy and vitamin C-dependent collagen hydroxylationFull bank topic Vitamin B12 deficiencyFree question Vitamin B12 deficiency lab pattern (elevated homocysteine and MMA)Full bank topic Vitamin B12 deficiency neurological mechanism (methylmalonyl-CoA mutase)Full bank topic Wernicke encephalopathy and thiamine-dependent oxidative decarboxylation cofactorsFull bank topic