MCQ on Proteins

🟢 Easy Level (1–20)

1. What are proteins made of?
   A) Sugars
   B) Amino acids ✅
   C) Fatty acids
   D) Nucleotides
   Explanation: Proteins are polymers of amino acids.
2. Which element is found in proteins but not in carbohydrates?
   A) Carbon
   B) Hydrogen
   C) Nitrogen ✅
   D) Oxygen
   Explanation: Nitrogen is unique to proteins due to amino groups.
3. Which of these is a structural protein?
   A) Hemoglobin
   B) Insulin
   C) Keratin ✅
   D) Amylase
   Explanation: Keratin provides structure to hair, nails, and skin.
4. What is the function of enzymes?
   A) Store genetic information
   B) Speed up chemical reactions ✅
   C) Store energy
   D) Transport oxygen
   Explanation: Enzymes are proteins that catalyze reactions.
5. Hemoglobin is an example of a:
   A) Hormone
   B) Structural protein
   C) Transport protein ✅
   D) Antibody
   Explanation: Hemoglobin transports oxygen in red blood cells.
6. Which of the following is a complete protein?
   A) Rice
   B) Wheat
   C) Egg ✅
   D) Corn
   Explanation: Eggs contain all essential amino acids.
7. The bond that links amino acids is called a:
   A) Glycosidic bond
   B) Peptide bond ✅
   C) Ester bond
   D) Hydrogen bond
   Explanation: Amino acids are linked by peptide bonds.
8. How many different amino acids are used to make proteins?
   A) 10
   B) 20 ✅
   C) 25
   D) 5
   Explanation: Proteins are made from 20 different amino acids.
9. Which part of an amino acid varies among different amino acids?
   A) Amino group
   B) Carboxyl group
   C) R group ✅
   D) Hydrogen atom
   Explanation: The R group defines the identity of the amino acid.
10. Which organ digests proteins first?
    A) Mouth
    B) Stomach ✅
    C) Small intestine
    D) Large intestine
    Explanation: Protein digestion begins in the stomach.
11. Which enzyme starts protein digestion?
    A) Amylase
    B) Lipase
    C) Pepsin ✅
    D) Trypsin
    Explanation: Pepsin is active in the acidic environment of the stomach.
12. Which protein is involved in muscle contraction?
    A) Keratin
    B) Myosin ✅
    C) Albumin
    D) Hemoglobin
    Explanation: Myosin interacts with actin to cause contraction.
13. Which protein is found in blood plasma and helps maintain osmotic pressure?
    A) Hemoglobin
    B) Albumin ✅
    C) Fibrinogen
    D) Myosin
    Explanation: Albumin maintains oncotic pressure in blood vessels.
14. Proteins are synthesized in which cell organelle?
    A) Nucleus
    B) Mitochondria
    C) Ribosomes ✅
    D) Golgi apparatus
    Explanation: Ribosomes are the sites of protein synthesis.
15. A protein that acts against pathogens is called:
    A) Enzyme
    B) Hormone
    C) Antibody ✅
    D) Neurotransmitter
    Explanation: Antibodies are immune proteins that fight infections.
16. Protein deficiency can cause which disease?
    A) Kwashiorkor ✅
    B) Rickets
    C) Scurvy
    D) Goiter
    Explanation: Kwashiorkor is caused by protein deficiency in children.
17. Which of the following is not a function of proteins?
    A) Energy storage ✅
    B) Enzymatic activity
    C) Structural support
    D) Hormonal signaling
    Explanation: Proteins are not primarily used for energy storage.
18. What is denaturation?
    A) Synthesis of protein
    B) Breakdown of proteins
    C) Loss of protein structure ✅
    D) Transport of proteins
    Explanation: Denaturation alters the protein’s shape and function.
19. Insulin is what type of protein?
    A) Enzyme
    B) Hormone ✅
    C) Structural
    D) Transport
    Explanation: Insulin is a peptide hormone regulating blood glucose.
20. Which structure level describes the sequence of amino acids?
    A) Primary ✅
    B) Secondary
    C) Tertiary
    D) Quaternary
    Explanation: The primary structure is the linear sequence of amino acids.

🟡 Moderate Level (21–40)

21. Which of the following is a fibrous protein?
    A) Myoglobin
    B) Hemoglobin
    C) Collagen ✅
    D) Insulin
    Explanation: Collagen provides structural support to connective tissue.
22. The secondary structure of protein is stabilized by:
    A) Ionic bonds
    B) Hydrogen bonds ✅
    C) Peptide bonds
    D) Disulfide bonds
    Explanation: Hydrogen bonds hold together alpha helices and beta sheets.
23. Which of these is an essential amino acid?
    A) Glycine
    B) Alanine
    C) Leucine ✅
    D) Tyrosine
    Explanation: Leucine must be obtained through the diet.
24. The quaternary structure of a protein refers to:
    A) Sequence of amino acids
    B) Folding of one polypeptide
    C) Arrangement of multiple polypeptides ✅
    D) Hydrogen bonding
    Explanation: Quaternary structure involves multiple polypeptide chains.
25. What type of bond forms between the sulfur atoms of cysteine residues?
    A) Hydrogen bond
    B) Disulfide bond ✅
    C) Ionic bond
    D) Peptide bond
    Explanation: Disulfide bonds stabilize tertiary structures.
26. Which of the following is a globular protein?
    A) Actin
    B) Hemoglobin ✅
    C) Collagen
    D) Keratin
    Explanation: Hemoglobin has a compact, spherical shape.
27. Protein digestion is completed in:
    A) Stomach
    B) Small intestine ✅
    C) Mouth
    D) Large intestine
    Explanation: Final digestion and absorption occur in the small intestine.
28. Zwitterions in proteins are formed due to:
    A) Acidic pH
    B) Basic pH
    C) Presence of both acidic and basic groups ✅
    D) No charged groups
    Explanation: Amino acids have both NH₃⁺ and COO⁻ groups at neutral pH.
29. Which protein is involved in blood clotting?
    A) Albumin
    B) Fibrinogen ✅
    C) Hemoglobin
    D) Myoglobin
    Explanation: Fibrinogen is converted to fibrin during clot formation.
30. At isoelectric point, a protein is:
    A) Positively charged
    B) Negatively charged
    C) Neutral ✅
    D) Denatured
    Explanation: The net charge of the protein is zero at its isoelectric point.
31. Which of the following is a conjugated protein?
    A) Keratin
    B) Hemoglobin ✅
    C) Actin
    D) Elastin
    Explanation: Hemoglobin has a heme (non-protein) group.
32. Trypsin acts in the:
    A) Mouth
    B) Stomach
    C) Small intestine ✅
    D) Large intestine
    Explanation: Trypsin is secreted into the small intestine.
33. The amino acid sequence is encoded by:
    A) DNA ✅
    B) RNA
    C) Ribosome
    D) Enzymes
    Explanation: DNA contains the genetic instructions for protein synthesis.
34. Protein turnover means:
    A) Protein denaturation
    B) Continuous breakdown and synthesis ✅
    C) Protein folding
    D) Protein absorption
    Explanation: Protein turnover is the dynamic process of protein renewal.
35. Which amino acid has a sulfur group?
    A) Serine
    B) Cysteine ✅
    C) Lysine
    D) Glutamine
    Explanation: Cysteine contains a thiol (-SH) group.
36. Which protein stores oxygen in muscles?
    A) Hemoglobin
    B) Myoglobin ✅
    C) Albumin
    D) Collagen
    Explanation: Myoglobin stores oxygen in muscle tissue.
37. Which test detects proteins in a sample?
    A) Biuret test ✅
    B) Benedict’s test
    C) Iodine test
    D) Sudan test
    Explanation: Biuret test gives a violet color in the presence of proteins.
38. A mutation changing one amino acid may affect the:
    A) Primary structure only
    B) Secondary structure only
    C) Tertiary structure
    D) All levels of structure ✅
    Explanation: A single change can impact folding and function.
39. Proteins with similar structures but different functions are called:
    A) Homologs ✅
    B) Paralogs
    C) Isozymes
    D) Peptides
    Explanation: Homologs share ancestry but may differ functionally.
40. Protein synthesis in the cytoplasm requires:
    A) tRNA
    B) Ribosomes
    C) mRNA
    D) All of the above ✅
    Explanation: All components are essential for protein translation.

🔴 Hard Level (41–50)

41. Which amino acid disrupts alpha helices?
    A) Glycine
    B) Serine
    C) Proline ✅
    D) Alanine
    Explanation: Proline causes kinks in helices due to its rigid ring.
42. The Ramachandran plot shows:
    A) Enzyme kinetics
    B) Protein folding energy
    C) Allowed dihedral angles ✅
    D) Disulfide linkages
    Explanation: It plots phi and psi angles of polypeptide chains.
43. Which protein acts as a molecular chaperone?
    A) Myosin
    B) Hsp70 ✅
    C) Actin
    D) Tubulin
    Explanation: Hsp70 helps other proteins fold correctly.
44. Which structure is disrupted first during denaturation?
    A) Primary
    B) Secondary ✅
    C) Peptide bonds
    D) Amino acid sequence
    Explanation: Hydrogen bonds in secondary structure break first.
45. Proteins are classified based on:
    A) Shape
    B) Function
    C) Composition
    D) All of the above ✅
    Explanation: Protein classification includes shape, function, and composition.
46. Which amino acid is often phosphorylated in signaling proteins?
    A) Tyrosine ✅
    B) Lysine
    C) Leucine
    D) Alanine
    Explanation: Tyrosine residues are phosphorylated during signal transduction.
47. Which amino acid has an imidazole group?
    A) Histidine ✅
    B) Arginine
    C) Tryptophan
    D) Glutamine
    Explanation: Histidine contains an imidazole side chain.
48. The SDS-PAGE technique separates proteins by:
    A) Shape
    B) Charge
    C) Molecular weight ✅
    D) Isoelectric point
    Explanation: SDS binds proteins and gives them uniform charge for size separation.
49. Which process occurs at the rough ER?
    A) Glycolysis
    B) Lipid synthesis
    C) Protein synthesis ✅
    D) DNA replication
    Explanation: Ribosomes on rough ER synthesize proteins.
50. Post-translational modification includes:
    A) Transcription
    B) Peptide bond formation
    C) Phosphorylation ✅
    D) RNA splicing
    Explanation: Modifications like phosphorylation occur after translation.