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.