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Quiz Biochemistry: DNA, proteins, enzymes and ATP

Eleven biochemistry questions on DNA, proteins, enzymes, ATP and metabolism. Verified facts with explainers covering codons, kinetics, and energy.

12 questions~6 minen
Q1 / 12
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How many nitrogenous bases are found in DNA?

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  1. Q1. How many nitrogenous bases are found in DNA?

    • 2
    • 3
    • 4
    • 5
    DNA contains 4 bases: adenine (A), thymine (T), guanine (G) and cytosine (C). They pair specifically — A with T (2 H-bonds) and G with C (3 H-bonds).

  2. Q2. Who discovered the double-helix structure of DNA?

    • Mendel & Morgan
    • Watson, Crick, Franklin & Wilkins
    • Pauling & Corey
    • Darwin & Wallace
    James Watson and Francis Crick published the double helix model in 1953, using X-ray diffraction data from Rosalind Franklin and Maurice Wilkins. Nobel Prize awarded in 1962.

  3. Q3. What is the monomer of a protein?

    • Nucleotide
    • Amino acid
    • Fatty acid
    • Monosaccharide
    Proteins are polymers of amino acids linked by peptide bonds. There are 20 standard amino acids encoded by DNA; their order determines folding and biological function.

  4. Q4. What does ATP stand for?

    • Adenosine TriPhosphate
    • Amino TriPolymer
    • Alanine TriPeptide
    • Adenine Tetra-Phosphate
    ATP = adenosine triphosphate, the universal energy currency of the cell. Hydrolysis ATP → ADP + Pi releases ~30.5 kJ/mol under standard conditions and powers most cellular work.

  5. Q5. What type of molecule is an enzyme (almost always)?

    • A lipid
    • A protein
    • A sugar
    • A nucleic acid
    Most enzymes are proteins — though some RNA molecules (ribozymes) also catalyze reactions. Enzymes can accelerate reactions by factors of 10⁶ to 10¹⁷ over the uncatalyzed rate.

  6. Q6. How many codons in the genetic code?

    • 20
    • 32
    • 64
    • 128
    There are 4³ = 64 codons (3-base combinations). 61 code for amino acids and 3 are stop codons (UAA, UAG, UGA). AUG (methionine) is the universal start codon.

  7. Q7. Which organelle is the main site of ATP production in animal cells?

    • Nucleus
    • Ribosome
    • Mitochondrion
    • Golgi apparatus
    Mitochondria run oxidative phosphorylation, producing about 30-32 ATP per glucose via the electron transport chain. They have their own circular DNA, inherited maternally.

  8. Q8. What is the complementary base of guanine in DNA?

    • Adenine
    • Thymine
    • Cytosine
    • Uracil
    Guanine pairs with cytosine via 3 hydrogen bonds, while adenine pairs with thymine via 2. This G-C bond strength is why GC-rich DNA regions have higher melting temperatures.

  9. Q9. What is the process by which mRNA is read to make a protein?

    • Replication
    • Transcription
    • Translation
    • Transduction
    Translation occurs in ribosomes, where mRNA codons are decoded by tRNAs carrying amino acids. A typical human ribosome adds about 6 amino acids per second.

  10. Q10. Which sugar is the primary energy fuel for cells?

    • Fructose
    • Sucrose
    • Glucose
    • Lactose
    Glucose C₆H₁₂O₆ is the central fuel. Glycolysis splits it into 2 pyruvates with a net yield of 2 ATP and 2 NADH, before oxidative phosphorylation completes the harvest.

  11. Q11. What does the Michaelis-Menten constant Km measure?

    • Maximum reaction rate
    • Substrate concentration at half Vmax
    • Enzyme molecular weight
    • Activation energy
    Km is the substrate concentration giving half the maximum velocity Vmax. A low Km signals high affinity between enzyme and substrate. The model was published in 1913.

  12. Q12. How many chromosomes does a human somatic cell normally contain?

    • 23
    • 44
    • 46
    • 48
    Human somatic cells carry 46 chromosomes arranged in 23 pairs, including XX (female) or XY (male). Gametes carry just 23 after meiosis, enabling fertilization to restore 46.

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