1. What are the basic monomer building blocks of proteins?
Correct Answer: B (Amino acids)
Proteins are unbranched polymers composed of amino acids linked together by peptide bonds.
Proteins are unbranched polymers composed of amino acids linked together by peptide bonds.
2. Which chemical bond joins amino acids together in a polypeptide chain?
Correct Answer: C (Peptide bond)
A peptide bond is a covalent amide bond formed via a condensation reaction between the carboxyl group of one amino acid and the amino group of another.
A peptide bond is a covalent amide bond formed via a condensation reaction between the carboxyl group of one amino acid and the amino group of another.
3. Which of the following elements is present in all proteins but absent in pure carbohydrates and lipids?
Correct Answer: A (Nitrogen)
All amino acids have an amino group (-NH₂), making nitrogen a defining element present in all proteins (~16% by mass).
All amino acids have an amino group (-NH₂), making nitrogen a defining element present in all proteins (~16% by mass).
4. How many standard amino acids are genetically encoded to synthesize proteins in living organisms?
Correct Answer: B (20)
There are 20 standard (canonical) amino acids specified by the universal genetic code.
There are 20 standard (canonical) amino acids specified by the universal genetic code.
5. The linear sequence of amino acids in a polypeptide represents its:
Correct Answer: A (Primary structure)
The primary structure is the exact linear sequence of amino acids ordered from the N-terminus to the C-terminus.
The primary structure is the exact linear sequence of amino acids ordered from the N-terminus to the C-terminus.
6. Which type of bonding stabilizes secondary structures such as alpha-helices and beta-sheets?
Correct Answer: C (Hydrogen bonds)
Secondary structures are stabilized by hydrogen bonding between the carbonyl oxygen (C=O) and amide hydrogen (N-H) of the polypeptide backbone.
Secondary structures are stabilized by hydrogen bonding between the carbonyl oxygen (C=O) and amide hydrogen (N-H) of the polypeptide backbone.
7. Which standard amino acid is achiral (lacks an asymmetric alpha-carbon)?
Correct Answer: C (Glycine)
Glycine has a single hydrogen atom as its side chain (-H), making its alpha-carbon symmetrical and optically inactive.
Glycine has a single hydrogen atom as its side chain (-H), making its alpha-carbon symmetrical and optically inactive.
8. Which two standard amino acids contain a sulfur atom in their side chains?
Correct Answer: A (Cysteine and Methionine)
Cysteine possesses a thiol (-SH) group, and Methionine possesses a thioether group.
Cysteine possesses a thiol (-SH) group, and Methionine possesses a thioether group.
9. Disulfide bonds (bridges) are formed between the side chains of which amino acid?
Correct Answer: B (Cysteine)
Covalent disulfide bonds form when two cysteine residues undergo oxidation, yielding a cystine dimer.
Covalent disulfide bonds form when two cysteine residues undergo oxidation, yielding a cystine dimer.
10. Hemoglobin is an example of a protein with which level of structural organization?
Correct Answer: D (Quaternary structure)
Hemoglobin is a tetramer composed of four distinct polypeptide subunits (two alpha and two beta chains).
Hemoglobin is a tetramer composed of four distinct polypeptide subunits (two alpha and two beta chains).
11. What is an amino acid called when it carries both a positive and a negative charge, with a net neutral charge?
Correct Answer: A (Zwitterion)
At physiological pH, amino acids exist as dipolar ions (zwitterions) with a protonated amino group (-NH₃⁺) and a deprotonated carboxyl group (-COO⁻).
At physiological pH, amino acids exist as dipolar ions (zwitterions) with a protonated amino group (-NH₃⁺) and a deprotonated carboxyl group (-COO⁻).
12. Which of the following is an essential amino acid in human nutrition?
Correct Answer: C (Leucine)
Essential amino acids (like Leucine, Isoleucine, and Lysine) cannot be synthesized de novo by the human body and must come from the diet.
Essential amino acids (like Leucine, Isoleucine, and Lysine) cannot be synthesized de novo by the human body and must come from the diet.
13. What chemical test is commonly used in laboratories to confirm the presence of peptide bonds and proteins?
Correct Answer: B (Biuret Test)
The Biuret reagent (alkaline copper sulfate) turns purple/violet in the presence of peptide bonds.
The Biuret reagent (alkaline copper sulfate) turns purple/violet in the presence of peptide bonds.
14. What occurs when a protein undergoes denaturation?
Correct Answer: B (Higher-order structures unfold while primary structure remains intact)
Denaturation disrupts secondary, tertiary, and quaternary conformations without cleaving covalent peptide bonds.
Denaturation disrupts secondary, tertiary, and quaternary conformations without cleaving covalent peptide bonds.
15. Which cellular organelle is the primary site of protein translation?
Correct Answer: C (Ribosome)
Ribosomes decode mRNA sequences into polypeptide chains using tRNA molecules during translation.
Ribosomes decode mRNA sequences into polypeptide chains using tRNA molecules during translation.
16. What is the most abundant structural protein in the human body?
Correct Answer: A (Collagen)
Collagen accounts for roughly 25-35% of total whole-body protein content, found in connective tissues, skin, tendons, and bones.
Collagen accounts for roughly 25-35% of total whole-body protein content, found in connective tissues, skin, tendons, and bones.
17. Which amino acid has a rigid cyclic side chain that often introduces “kinks” or breaks in alpha-helices?
Correct Answer: B (Proline)
Proline’s nitrogen atom is bonded into a 5-membered ring, restricting torsional angles and acting as a secondary structure “helix breaker.”
Proline’s nitrogen atom is bonded into a 5-membered ring, restricting torsional angles and acting as a secondary structure “helix breaker.”
18. The pH value at which an amino acid or protein possesses zero net electric charge is known as its:
Correct Answer: C (Isoelectric point (pI))
At the isoelectric point (pI), the positive and negative charges on the protein balance out completely, minimizing its solubility in water.
At the isoelectric point (pI), the positive and negative charges on the protein balance out completely, minimizing its solubility in water.
19. Which specialized class of proteins assists other nascent polypeptide chains to fold properly in vivo?
Correct Answer: A (Molecular chaperones (Chaperonins))
Chaperones (such as Hsp70 and GroEL) prevent inappropriate aggregation and facilitate correct folding.
Chaperones (such as Hsp70 and GroEL) prevent inappropriate aggregation and facilitate correct folding.
20. Which of the following is a fibrous, insoluble protein?
Correct Answer: C (Keratin)
Keratin forms hair, nails, and feathers; it is an insoluble, fibrous structural protein.
Keratin forms hair, nails, and feathers; it is an insoluble, fibrous structural protein.
21. A non-protein organic or metallic component tightly bound to a conjugated protein is known as a:
Correct Answer: A (Prosthetic group)
A prosthetic group (e.g., the heme group in hemoglobin or iron-sulfur clusters) is essential for the biological activity of conjugated proteins.
A prosthetic group (e.g., the heme group in hemoglobin or iron-sulfur clusters) is essential for the biological activity of conjugated proteins.
22. What plot maps the allowed dihedral angles (phi φ and psi ψ) of a polypeptide backbone?
Correct Answer: B (Ramachandran plot)
The Ramachandran plot visualizes energetically permissible regions for backbone torsion angles φ and ψ in protein conformations.
The Ramachandran plot visualizes energetically permissible regions for backbone torsion angles φ and ψ in protein conformations.
23. Which amino acid residue is the universal starting amino acid during eukaryotic translation?
Correct Answer: A (Methionine (AUG codon))
The AUG start codon directs the incorporation of Methionine in eukaryotes (and N-formylmethionine in bacteria).
The AUG start codon directs the incorporation of Methionine in eukaryotes (and N-formylmethionine in bacteria).
24. What reagent reacts with free alpha-amino groups to produce a deep purple/blue complex (Ruhemann’s purple)?
Correct Answer: B (Ninhydrin)
Ninhydrin is widely used in chromatography and forensics to detect free amino acids and latent fingerprints.
Ninhydrin is widely used in chromatography and forensics to detect free amino acids and latent fingerprints.
25. Which of the following amino acids possesses an aromatic side chain?
Correct Answer: C (Tryptophan)
Phenylalanine, Tyrosine, and Tryptophan contain aromatic rings in their side chains and absorb UV light strongly near 280 nm.
Phenylalanine, Tyrosine, and Tryptophan contain aromatic rings in their side chains and absorb UV light strongly near 280 nm.
26. What term describes infectious, misfolded proteins that induce normal proteins to misfold (e.g., in Mad Cow disease)?
Correct Answer: B (Prions)
Prions are proteinaceous infectious particles containing no nucleic acid genome.
Prions are proteinaceous infectious particles containing no nucleic acid genome.
27. Which predominant secondary structure gives silk fibroin its high tensile strength and flexibility?
Correct Answer: B (Beta-pleated sheet)
Silk fibroin is rich in anti-parallel beta-pleated sheets packed closely with small side chain residues like Glycine and Alanine.
Silk fibroin is rich in anti-parallel beta-pleated sheets packed closely with small side chain residues like Glycine and Alanine.
28. Which of the following is an example of a post-translational modification (PTM) of proteins?
Correct Answer: C (Phosphorylation)
Phosphorylation (adding a phosphate group via protein kinases) is a common covalent modification regulating enzyme activity and signaling.
Phosphorylation (adding a phosphate group via protein kinases) is a common covalent modification regulating enzyme activity and signaling.
29. The main driving force for the folding of globular proteins into their tertiary structures in aqueous environments is:
Correct Answer: A (Hydrophobic interaction / hydrophobic collapse)
Hydrophobic nonpolar side chains bury themselves inside the interior core away from water, maximizing overall thermodynamic stability.
Hydrophobic nonpolar side chains bury themselves inside the interior core away from water, maximizing overall thermodynamic stability.
30. What type of protein acts as a biological catalyst to accelerate biochemical reactions without being consumed?
Correct Answer: B (Enzyme)
Enzymes are specialized protein catalysts that lower activation energy to dramatically increase reaction rates.
Enzymes are specialized protein catalysts that lower activation energy to dramatically increase reaction rates.