Chemical nature of proteins MCQs With Answer

Chemical nature of proteins MCQs With Answer is a focused revision set designed for B. Pharm students to strengthen understanding of amino acids, peptide bonds, protein structure and folding, and related physicochemical properties. This resource emphasizes chemical principles such as side-chain reactivity, acid–base behavior, isoelectric point, hydrophobic interactions, disulfide linkages, prosthetic groups, post‑translational modifications, denaturation, and analytical techniques including electrophoresis, chromatography and sequencing. Questions target both conceptual depth and pharmaceutical relevance, linking molecular features to biological function and drug interactions. Answers include concise chemical rationale relevant to pharmaceutical applications and drug design. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which atom in the peptide bond has partial double-bond character resulting in planarity of the peptide linkage?

• Alpha carbon (Cα)
• Carbonyl carbon (C=O)
• Peptide bond carbon–nitrogen (C–N)
• Amide hydrogen (N–H)

Correct Answer: Peptide bond carbon–nitrogen (C–N)

Q2. The isoelectric point (pI) of a protein is defined as:

• The pH at which the protein has maximum solubility
• The pH at which the net charge of the protein is zero
• The pH of maximum enzyme activity for that protein
• The pH at which the protein aggregates irreversibly

Correct Answer: The pH at which the net charge of the protein is zero

Q3. Which amino acid is unique for forming disulfide bonds that stabilize tertiary structure?

• Methionine
• Cysteine
• Tryptophan
• Proline

Correct Answer: Cysteine

Q4. In protein secondary structure, which interaction primarily stabilizes alpha helices and beta sheets?

• Hydrophobic interactions between side chains
• Peptide backbone hydrogen bonding
• Disulfide bond formation
• Ionic bonds between side chains

Correct Answer: Peptide backbone hydrogen bonding

Q5. A zwitterion refers to an amino acid form that:

• Has a net positive charge
• Has a net negative charge
• Has both positive and negative charges but net neutral
• Is fully protonated on all functional groups

Correct Answer: Has both positive and negative charges but net neutral

Q6. Which method is commonly used to determine the primary sequence of a protein by Edman degradation?

• Sequential removal of N-terminal amino acids
• Cleavage at methionine residues only
• Mass spectrometric fragmentation of the entire protein
• Hydrolysis followed by gas chromatography

Correct Answer: Sequential removal of N-terminal amino acids

Q7. Which property of amino acid side chains most influences protein folding into a native conformation?

• Electronegativity of the alpha carbon
• Hydrophobicity/hydrophilicity balance
• Isotopic composition of the side chain atoms
• Length of the peptide backbone

Correct Answer: Hydrophobicity/hydrophilicity balance

Q8. Which reagent specifically breaks disulfide bonds in proteins?

• Sodium dodecyl sulfate (SDS)
• Dithiothreitol (DTT)
• Urea
• EDTA

Correct Answer: Dithiothreitol (DTT)

Q9. Which amino acid is considered the helix breaker due to its rigid cyclic structure?

• Glycine
• Proline
• Alanine
• Leucine

Correct Answer: Proline

Q10. Which technique separates proteins based on molecular weight under denaturing conditions?

• Isoelectric focusing
• SDS-PAGE
• Size-exclusion chromatography in native buffer
• Two-dimensional NMR spectroscopy

Correct Answer: SDS-PAGE

Q11. Which of the following is a nonpolar, aliphatic amino acid frequently found in protein cores?

• Serine
• Valine
• Asparagine
• Histidine

Correct Answer: Valine

Q12. Which interaction is most important for stabilizing the quaternary structure of hemoglobin?

• Covalent peptide bonds between subunits
• Hydrogen bonds and hydrophobic interactions between subunits
• Disulfide bonds linking the four subunits
• Van der Waals forces only at the heme

Correct Answer: Hydrogen bonds and hydrophobic interactions between subunits

Q13. The Ramachandran plot is used to visualize which features of a protein?

• Side chain rotamer distributions
• Main-chain dihedral angles phi and psi
• Relative hydrophobicity across the sequence
• Temperature factors from X-ray crystallography

Correct Answer: Main-chain dihedral angles phi and psi

Q14. Which amino acid side chain has a pKa near physiological pH and often participates in enzyme catalysis?

• Lysine
• Histidine
• Aspartate
• Glutamate

Correct Answer: Histidine

Q15. Post-translational modification that adds a phosphate group typically occurs on which residues?

• Glycine, alanine, valine
• Serine, threonine, tyrosine
• Proline and hydroxyproline
• Phenylalanine and tryptophan

Correct Answer: Serine, threonine, tyrosine

Q16. Which statement about peptide bond hydrolysis is correct?

• It is spontaneous under physiological conditions without catalysts
• Proteases catalyze peptide bond hydrolysis by lowering activation energy
• Peptide bonds hydrolyze only under strong alkaline conditions
• Hydrolysis results in formation of ether bonds

Correct Answer: Proteases catalyze peptide bond hydrolysis by lowering activation energy

Q17. Glycosylation as a protein modification typically affects which property?

• Only the primary sequence
• Protein solubility, stability and recognition
• Replacement of peptide bonds with glycosidic bonds
• Conversion into purely hydrophobic molecules

Correct Answer: Protein solubility, stability and recognition

Q18. Which amino acid has no chiral center and contributes flexibility to polypeptide chains?

• Glycine
• Alanine
• Isoleucine
• Threonine

Correct Answer: Glycine

Q19. Which factor most directly affects the pI of a peptide?

• The sequence and pKa values of ionizable groups
• The molecular weight of the peptide
• Presence of aromatic residues only
• The peptide’s absorbance at 280 nm

Correct Answer: The sequence and pKa values of ionizable groups

Q20. In protein denaturation, which agent primarily disrupts hydrogen bonding and secondary structures?

• Reducing agents like β-mercaptoethanol
• Chaotropic agents like urea
• Metal ions like Mg2+
• Lipid bilayer insertion

Correct Answer: Chaotropic agents like urea

Q21. Which amino acid side chain is positively charged at physiological pH?

• Aspartate
• Glutamate
• Lysine
• Tyrosine

Correct Answer: Lysine

Q22. Metalloproteins contain metal ions that commonly act as:

• Structural stabilizers and catalytic cofactors
• Sources of peptide bonds
• Buffers against pH change
• Permanent inhibitors of enzymatic activity

Correct Answer: Structural stabilizers and catalytic cofactors

Q23. Which analytical technique provides information on protein secondary structure in solution?

• Circular dichroism (CD) spectroscopy
• X-ray crystallography only
• MALDI-TOF mass spectrometry
• UV-Vis absorbance at 260 nm

Correct Answer: Circular dichroism (CD) spectroscopy

Q24. Which amino acid side chains are most likely to form salt bridges?

• Nonpolar aliphatic residues
• Aromatic residues
• Positively and negatively charged residues (e.g., Lys and Asp)
• Neutral polar residues only

Correct Answer: Positively and negatively charged residues (e.g., Lys and Asp)

Q25. Which reagent is used to cleave peptide bonds at methionine residues during protein sequencing?

• Cyanogen bromide (CNBr)
• Tryptic digestion
• Edman reagent
• Ammonium hydroxide

Correct Answer: Cyanogen bromide (CNBr)

Q26. Which structural level describes the linear sequence of amino acids in a protein?

• Primary structure
• Secondary structure
• Tertiary structure
• Quaternary structure

Correct Answer: Primary structure

Q27. Which phenomenon explains why hydrophobic amino acids are usually buried inside proteins?

• Maximization of peptide bond flexibility
• Hydrophobic effect driven by entropy of water
• Covalent crosslinking with solvent molecules
• Electrostatic attraction to polar side chains

Correct Answer: Hydrophobic effect driven by entropy of water

Q28. Which amino acid residue is commonly phosphorylated in eukaryotic signal transduction?

• Phenylalanine
• Serine
• Leucine
• Proline

Correct Answer: Serine

Q29. The term “conjugated protein” refers to a protein that:

• Has only peptide bonds
• Contains a non-protein prosthetic group
• Is formed exclusively of glycine residues
• Has been chemically synthesized

Correct Answer: Contains a non-protein prosthetic group

Q30. In acid-base titration of amino acids, the midpoint of a buffering region corresponds to:

• Half-neutralization where pH = pKa
• Point of complete ionization of all groups
• Isoelectric point
• Point of maximum precipitation

Correct Answer: Half-neutralization where pH = pKa

Q31. Which technique separates proteins based on isoelectric point?

• SDS-PAGE
• Isoelectric focusing (IEF)
• Gel filtration chromatography
• Affinity chromatography using antibodies

Correct Answer: Isoelectric focusing (IEF)

Q32. Which amino acid side chain can form hydrogen bonds and is polar but uncharged at physiological pH?

• Asparagine
• Leucine
• Valine
• Methionine

Correct Answer: Asparagine

Q33. Which of the following best describes a prosthetic group?

• A non-protein component permanently attached to a protein
• A temporary substrate molecule bound in active site
• A lipid tail that targets protein to membranes
• An unstructured peptide extension

Correct Answer: A non-protein component permanently attached to a protein

Q34. Which bond rotation is restricted causing planar nature of peptide unit?

• Rotation about Cα–C bond
• Rotation about C–N peptide bond
• Rotation about N–H bond
• Rotation about C=O double bond

Correct Answer: Rotation about C–N peptide bond

Q35. Which amino acid side chain often participates in metal ion coordination within proteins?

• Phenylalanine
• Histidine
• Alanine
• Glycine

Correct Answer: Histidine

Q36. Which denaturing detergent also imparts a negative charge to proteins for electrophoresis?

• Triton X-100
• SDS (sodium dodecyl sulfate)
• Urea
• Guanidine hydrochloride

Correct Answer: SDS (sodium dodecyl sulfate)

Q37. Which technique is most suitable for identifying post-translational modifications on proteins?

• Edman degradation only
• Mass spectrometry
• Basic amino acid analysis
• Ultraviolet absorbance at 280 nm

Correct Answer: Mass spectrometry

Q38. Which amino acid side chain can be ionized and contributes to catalytic triad in serine proteases?

• Serine, histidine, aspartate
• Glycine, alanine, valine
• Tyrosine, tryptophan, phenylalanine
• Proline, lysine, methionine

Correct Answer: Serine, histidine, aspartate

Q39. Which statement about glycine and proline in protein structure is correct?

• Both favor formation of alpha helices equally
• Glycine provides flexibility; proline induces kinks
• Proline stabilizes beta strands by hydrogen bonding
• Glycine is bulky and destabilizes turns

Correct Answer: Glycine provides flexibility; proline induces kinks

Q40. Which parameter is directly measured by Bradford assay for protein quantification?

• Intrinsic tryptophan fluorescence
• Binding of Coomassie Brilliant Blue to proteins
• Absorbance at 260 nm
• Enzymatic activity per mg protein

Correct Answer: Binding of Coomassie Brilliant Blue to proteins

Q41. Which factor does not typically affect protein solubility significantly?

• pH relative to pI
• Temperature
• Presence of specific salts and ionic strength
• Chirality of side chain carbon isotopes

Correct Answer: Chirality of side chain carbon isotopes

Q42. Which amino acids are aromatic and absorb UV light at ~280 nm useful for protein estimation?

• Glycine, alanine, serine
• Tryptophan, tyrosine, phenylalanine
• Asparagine, glutamine, histidine
• Lysine, arginine, histidine

Correct Answer: Tryptophan, tyrosine, phenylalanine

Q43. Which mechanism explains chaperone-assisted protein folding?

• Chaperones form permanent covalent attachments to proteins
• Chaperones prevent aggregation and provide isolated folding environments
• Chaperones degrade misfolded proteins by proteolysis only
• Chaperones change amino acid sequences to improve folding

Correct Answer: Chaperones prevent aggregation and provide isolated folding environments

Q44. Which amino acid derivative forms when serine residues are phosphorylated?

• Sulfated-serine
• Phosphoserine
• N-acetylserine
• Hydroxyserine

Correct Answer: Phosphoserine

Q45. Which chromatographic method separates proteins mainly by size under native conditions?

• Ion-exchange chromatography
• Size-exclusion (gel filtration) chromatography
• Affinity chromatography using metal chelation
• Reverse-phase HPLC

Correct Answer: Size-exclusion (gel filtration) chromatography

Q46. In acid hydrolysis of proteins for amino acid analysis, which amino acid is destroyed or partially lost?

• Leucine
• Tryptophan
• Alanine
• Proline

Correct Answer: Tryptophan

Q47. Which feature distinguishes fibrous proteins from globular proteins?

• Fibrous proteins are generally soluble and enzymatically active
• Fibrous proteins have elongated structures and structural roles
• Globular proteins always form fibers in tissues
• Globular proteins are exclusively extracellular

Correct Answer: Fibrous proteins have elongated structures and structural roles

Q48. Which functional group on amino acids participates in transamination reactions during amino acid metabolism?

• Carboxyl group only
• Amino group (–NH2)
• Sulfhydryl group
• Hydroxyl group

Correct Answer: Amino group (–NH2)

Q49. Which type of bond formation is involved in glycoprotein linkage to a carbohydrate?

• Peptide bond between sugar and amino acid
• Glycosidic or N-/O-linkage to amino acid side chains
• Disulfide bond between sugar and cysteine
• Phosphodiester bond linking sugar to serine

Correct Answer: Glycosidic or N-/O-linkage to amino acid side chains

Q50. Which concept describes the large number of possible conformations a polypeptide could adopt versus the rapid folding observed in vivo?

• Hunziker paradox
• Levinthal paradox
• Arrhenius principle
• Pauling conundrum

Correct Answer: Levinthal paradox

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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