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Quizzes > Science

Biochemistry trivia: test your knowledge

Quick, free quiz with biochemistry questions and answers. Instant results.

Editorial: Review CompletedCreated By: Jennifer HammUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper cutout style biochemistry quiz scene with DNA helix, molecular structures, test tubes on golden yellow background

This biochemistry quiz helps you check your grasp of enzymes, metabolic pathways, and molecular interactions in minutes, and spot topics to review. Answer short questions at your own pace. For extra practice, try our general chemistry quiz, explore biology quiz with answers, or build context with a nutrition knowledge test.

What is the pH of a neutral aqueous solution at 25°C?
1.0
6.0
14.0
7.0
Pure water autoionizes to produce equal concentrations of H+ and OH - ions at 25°C. The pH is defined as the negative log of the hydrogen ion concentration. In pure water, [H+] = 1 × 10?? M, giving a pH of 7.0.
Which amino acid is achiral?
Alanine
Glycine
Leucine
Valine
Glycine has two hydrogen atoms attached to its alpha carbon, making it the only achiral amino acid. All other standard amino acids have four different substituents on the alpha carbon. Chirality arises when a carbon has four unique groups attached.
Which of the following is a purine base in nucleic acids?
Thymine
Cytosine
Adenine
Uracil
Purines are two-ring nitrogenous bases; adenine and guanine are purines. Cytosine, thymine, and uracil are pyrimidines, which consist of a single ring. Adenine pairs with thymine in DNA and with uracil in RNA via hydrogen bonds.
The primary structure of a protein is determined by:
Hydrogen bonds
Disulfide bonds
Peptide bonds
Hydrophobic interactions
Primary structure refers to the linear sequence of amino acids in a polypeptide. These amino acids are linked by peptide (amide) bonds formed via dehydration synthesis. Higher-order structures arise from hydrogen bonds, disulfide bridges, and hydrophobic interactions.
Magnesium ion acting as a cofactor in enzymatic reactions is an example of a:
Vitamin cofactor
Prosthetic group
Coenzyme
Metal ion cofactor
Metal ion cofactors, such as Mg²?, assist enzyme activity by stabilizing negative charges and participating in catalysis. They are inorganic ions, distinct from organic coenzymes or prosthetic groups. Magnesium is essential for kinases and many nucleotide?binding enzymes.
Which monomer makes up DNA?
Glucose molecules
Deoxyribonucleotides
Amino acids
Ribonucleotides
DNA is a polymer of deoxyribonucleotides, each composed of a deoxyribose sugar, phosphate group, and nitrogenous base. Ribonucleotides are the monomers of RNA. Amino acids form proteins, and glucose forms polysaccharides.
What is the Henderson-Hasselbalch equation primarily used for?
Estimating molecular weight
Calculating enzyme velocity
Predicting protein folding
Determining buffer pH
The Henderson - Hasselbalch equation relates pH, pKa, and the ratio of conjugate base to acid in a buffer system. It is essential for calculating the pH of solutions containing weak acids and their conjugate bases. It is not used in enzyme kinetics or protein structure prediction.
Which vitamin is water-soluble?
Vitamin D
Vitamin A
Vitamin C
Vitamin E
Vitamin C (ascorbic acid) is water-soluble and must be regularly consumed as it is not stored in large amounts in the body. Vitamins A, D, and E are fat-soluble, stored in liver and adipose tissue. Water-soluble vitamins are excreted in urine when in excess.
Competitive inhibition of an enzyme typically results in which change to Michaelis-Menten parameters?
Increased Km, decreased Vmax
Increased Km, unchanged Vmax
Unchanged Km, decreased Vmax
Decreased Km, decreased Vmax
Competitive inhibitors bind the enzyme's active site, raising the apparent Km (lower affinity for substrate) because more substrate is needed to reach half Vmax. Vmax remains unchanged because high substrate concentrations outcompete the inhibitor.
Which metabolic pathway is the primary source of NADPH in cells?
Pentose phosphate pathway
Glycolysis
Citric acid cycle
?-oxidation
The oxidative phase of the pentose phosphate pathway generates NADPH by oxidizing glucose-6-phosphate. NADPH is vital for reductive biosynthesis and antioxidant defense. Glycolysis and the citric acid cycle produce NADH, not NADPH.
What does Km represent in Michaelis-Menten kinetics?
Inhibitor concentration for half-maximal effect
Maximum reaction velocity
Enzyme turnover number
Substrate concentration at half Vmax
Km is the substrate concentration at which the reaction velocity is half of Vmax. It reflects the affinity of enzyme for substrate: lower Km indicates higher affinity. It is not related to inhibitor concentration or kcat.
Which molecule is an allosteric activator of phosphofructokinase-1 (PFK-1) in glycolysis?
Fructose-2,6-bisphosphate
Glucose-6-phosphate
ATP
Citrate
Fructose-2,6-bisphosphate is a potent allosteric activator of PFK-1, enhancing glycolytic flux. ATP and citrate act as negative effectors by signaling high energy status. Glucose-6-phosphate regulates hexokinase, not PFK-1.
Which amino acid side chain contains a thiol (-SH) group?
Methionine
Serine
Cysteine
Threonine
Cysteine has a thiol side chain, which can form disulfide bonds critical for protein tertiary structure. Methionine contains a thioether, not a free thiol. Serine and threonine have hydroxyl groups.
Which lipid molecule is amphipathic, having both hydrophilic and hydrophobic regions?
Waxes
Triglyceride
Cholesterol
Phospholipid
Phospholipids have a hydrophilic phosphate head and hydrophobic fatty acid tails, making them essential for bilayer membranes. Cholesterol is mostly hydrophobic, triglycerides are nonpolar storage fats, and waxes are entirely hydrophobic.
How many NADH molecules are produced per acetyl-CoA in the citric acid cycle?
1
2
3
4
Each acetyl-CoA oxidation in the TCA cycle generates three NADH (from isocitrate dehydrogenase, ?-ketoglutarate dehydrogenase, and malate dehydrogenase). One FADH? and one GTP (or ATP) are also produced.
Which enzyme is the primary rate-limiting step of glycolysis?
Pyruvate kinase
Aldolase
Phosphofructokinase-1
Hexokinase
Phosphofructokinase-1 (PFK-1) catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and is the major regulatory step in glycolysis. It is allosterically controlled by cellular energy levels. Hexokinase and pyruvate kinase are regulated but not the primary rate-limiting enzymes.
Where in the cell does the urea cycle occur?
Nucleus
Mitochondria only
Both mitochondria and cytosol
Cytosol only
The urea cycle begins in the mitochondrial matrix and finishes in the cytosol. Carbamoyl phosphate synthetase I and ornithine transcarbamoylase act in mitochondria; remaining enzymes function in cytosol. This compartmentalization is essential for nitrogen disposal.
Which type of bond stabilizes the ?-helix secondary structure of proteins?
Ionic bonds
Van der Waals interactions
Hydrogen bonds
Disulfide bridges
Hydrogen bonds form between the carbonyl oxygen of one amino acid and the amide hydrogen four residues ahead, stabilizing the ?-helix. Ionic and disulfide bonds contribute to tertiary structure, not the regular helix backbone.
Which coenzyme is required by transaminase enzymes to transfer amino groups?
Coenzyme A
Pyridoxal phosphate (PLP)
FAD
NADH
Pyridoxal phosphate (PLP), derived from vitamin B6, forms a Schiff base with the amino acid substrate, enabling amino group transfer. It is essential for aminotransferase activity. NADH and FAD are redox cofactors, not involved in transamination. PLP function
Which enzyme catalyzes the fixation of CO? in the Calvin cycle of photosynthesis?
Glucose-6-phosphate dehydrogenase
Malate dehydrogenase
Phosphoenolpyruvate carboxylase
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
Rubisco catalyzes the carboxylation of ribulose-1,5-bisphosphate, the first step in CO? fixation in the Calvin cycle. It is the most abundant enzyme on Earth. PEP carboxylase functions in C4 plants and malate dehydrogenase in the TCA cycle.
How many ATP molecules are generated per FADH? during oxidative phosphorylation?
3.0
1.0
2.5
1.5
Each FADH? donates electrons to complex II in the electron transport chain, pumping fewer protons than NADH. This yields approximately 1.5 ATP per FADH?. NADH yields about 2.5 ATP due to higher proton translocation.
Which sugar is classified as a ketose?
Galactose
Glucose
Fructose
Mannose
Ketoses have a ketone functional group on the second carbon. Fructose is the common dietary ketose. Glucose, galactose, and mannose are aldoses, containing an aldehyde group at carbon 1.
Protein tertiary structure is primarily determined by:
Ribosomal chaperones
Primary amino acid sequence
Molecular crowding
Heat shock proteins
The primary sequence dictates how side chains interact, driving folding into the unique tertiary conformation. While chaperones assist folding in vivo, the amino acid sequence contains the information for the final structure. Heat shock proteins prevent misfolding but do not define the fold.
Which cofactor is uniquely used by methylmalonyl-CoA mutase to catalyze rearrangements via a radical mechanism?
Thiamine pyrophosphate
Flavin adenine dinucleotide
Biotin
Adenosylcobalamin (coenzyme B12)
Methylmalonyl-CoA mutase uses adenosylcobalamin (coenzyme B??) to generate a 5?-deoxyadenosyl radical, enabling carbon skeleton rearrangements. This radical-based mechanism is unique among B??-dependent enzymes. Thiamine and biotin catalyze different types of reactions.
Which irreversible enzyme in gluconeogenesis bypasses the glycolytic phosphofructokinase-1 step?
Pyruvate kinase
Fructose-1,6-bisphosphatase
Phosphoglycerate kinase
Hexokinase
Fructose-1,6-bisphosphatase hydrolyzes fructose-1,6-bisphosphate to fructose-6-phosphate, bypassing the irreversible PFK-1-catalyzed step in glycolysis. This reaction is a key regulatory point in gluconeogenesis. Hexokinase and pyruvate kinase are bypassed by other enzymes.
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Study Outcomes

  1. Understand Foundational Biomolecule Structures -

    Identify the building blocks of life by distinguishing proteins, lipids, carbohydrates, and nucleic acids through basic biochemistry questions and examples.

  2. Analyze Enzymatic Mechanisms -

    Break down enzyme kinetics and regulation scenarios to solve biochemistry questions and answers with confidence in any biochemistry quiz challenge.

  3. Apply Metabolic Pathway Logic -

    Map and interpret major pathways like glycolysis and the citric acid cycle, answering targeted biochemical questions on energy production and metabolite flow.

  4. Evaluate Real-World Biochemical Scenarios -

    Translate complex molecular data into practical applications, using fun biochemistry trivia to reinforce critical thinking in everyday contexts.

  5. Strengthen Problem-Solving Skills -

    Engage with adaptive basic biochemistry questions to refine analytical techniques and measure your progress in this engaging biochemistry quiz.

  6. Interpret Experimental Data -

    Read and assess graphs, tables, and reaction schemes, applying your knowledge through biochemical questions that mirror scientific research methodologies.

Cheat Sheet

  1. Michaelis-Menten Kinetics -

    Understanding the relationship between reaction rate and substrate concentration is crucial for enzyme function, as described in Lehninger Principles of Biochemistry. The equation v = Vmax[S]/(Km + [S]) models this behavior, where Km is the substrate concentration at half Vmax. Remember the mnemonic "KMatches Substrate" to recall that Km reflects affinity for the substrate.

  2. Glycolysis Rate-Limiting Steps -

    Hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase control the flux through glycolysis according to Harvard Medical School resources. PFK-1 is allosterically activated by AMP and inhibited by ATP and citrate, ensuring energy balance. Reviewing these regulatory points helps predict how cells adjust to energy demands.

  3. Henderson-Hasselbalch Equation -

    The formula pH = pKa + log([A - ]/[HA]) explains buffer behavior in physiological systems, as outlined by the NCBI Bookshelf. Practicing calculations with phosphate or bicarbonate buffers makes acid - base balance intuitive. This equation is key for predicting pH changes in metabolic pathways and experimental assays.

  4. Citric Acid Cycle Energy Yield -

    Each turn of the cycle oxidizes one acetyl-CoA to produce 3 NADH, 1 FADH2, and 1 GTP, based on IUBMB data. Converting these to ATP yields (~2.5 ATP per NADH and ~1.5 ATP per FADH2) gives about 10 ATP per acetyl-CoA. Visualizing the cycle as an energy factory helps solidify how cells harvest reducing equivalents.

  5. Amino Acid Essentiality Mnemonic -

    Use "PVT TIM HALL" (Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine) from the University of Cambridge to recall essential amino acids. Categorizing them by side-chain properties (hydrophobic, polar, charged) aids in predicting protein structure and function. This shortcut is a go-to for metabolic and nutrition questions.

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