Part 2 — Proteins, Carbohydrates, Lipids & Enzyme Classifications (Q26–50)

Q26.

Proteins are polymers of:
A. Amino acids ✅
B. Nucleotides
C. Monosaccharides
D. Fatty acids

Explanation:

A. Amino acids (Correct): Proteins are polypeptides formed by amino acids linked by peptide bonds.
B. Nucleotides: Polymers of nucleotides form nucleic acids.
C. Monosaccharides: Polysaccharides.
D. Fatty acids: Lipids, not proteins.

Q27.

Which level of protein structure is maintained by hydrogen bonds between C=O and N–H groups of backbone?
A. Primary
B. Secondary ✅
C. Tertiary
D. Quaternary

Explanation:

A. Primary: Linear sequence of amino acids.
B. Secondary (Correct): Alpha-helices and beta-pleated sheets stabilized by hydrogen bonding.
C. Tertiary: R-group interactions (ionic, hydrophobic, disulfide).
D. Quaternary: Arrangement of multiple polypeptide chains.

Q28.

The alpha-helix is stabilized by:
A. Hydrogen bonds between adjacent side chains
B. Hydrogen bonds between every 4th amino acid along backbone ✅
C. Disulfide bonds
D. Hydrophobic interactions

Explanation:

**A. Side-chain bonds stabilize tertiary structure, not alpha helix.
**B. Correct — backbone hydrogen bonds between C=O and N–H groups of amino acids four residues apart.
**C. Disulfide bonds stabilize tertiary/quaternary structure.
**D. Hydrophobic interactions stabilize tertiary structure.

Q29.

Globular proteins differ from fibrous proteins in being:
A. Insoluble in water
B. Generally structural
C. Usually spherical and soluble ✅
D. Linear polypeptide chains only

Explanation:

A. Insoluble: Fibrous proteins are insoluble; globular are soluble.
**B. Structural role = fibrous (collagen, keratin).
**C. Correct — globular proteins (enzymes, hormones) are compact, folded, soluble.
**D. Linear chains only = fibrous proteins.

Q30.

Which is a conjugated protein?
A. Hemoglobin ✅
B. Collagen
C. Keratin
D. Myosin

Explanation:

A. Hemoglobin (Correct): Protein + prosthetic group (heme).
B. Collagen, C. Keratin, D. Myosin: Simple proteins made solely of amino acids, no non-protein part.

Q31.

Denaturation of proteins involves:
A. Breaking peptide bonds
B. Loss of secondary, tertiary, quaternary structure without breaking primary sequence ✅
C. Hydrolysis into amino acids
D. Addition of amino groups

Explanation:

**A. Peptide bonds remain intact.
**B. Correct — denaturation disrupts non-covalent bonds, losing shape and function but not primary sequence.
**C. Hydrolysis = complete breakdown, not denaturation.
**D. Not relevant.

Q32.

Which carbohydrate is a reducing sugar?
A. Sucrose
B. Glucose ✅
C. Cellulose
D. Starch

Explanation:

A. Sucrose: Non-reducing because no free anomeric carbon.
B. Glucose (Correct): Has free aldehyde group in solution → reducing sugar.
C. Cellulose: Polysaccharide, non-reducing.
D. Starch: Non-reducing polysaccharide.

Q33.

Which disaccharide is composed of glucose + fructose?
A. Lactose
B. Maltose
C. Sucrose ✅
D. Cellobiose

Explanation:

A. Lactose: Glucose + galactose.
B. Maltose: Glucose + glucose (α-1,4).
C. Sucrose (Correct): Glucose + fructose.
D. Cellobiose: Glucose + glucose (β-1,4).

Q34.

Which storage polysaccharide is found in animals?
A. Glycogen ✅
B. Starch
C. Cellulose
D. Inulin

Explanation:

A. Glycogen (Correct): Storage carbohydrate in liver and muscles of animals.
B. Starch: Plant storage polysaccharide.
C. Cellulose: Structural in plants.
D. Inulin: Storage carbohydrate in some plants (e.g., Dahlia).

Q35.

Which lipid forms the major part of cell membranes?
A. Triacylglycerol
B. Phospholipid ✅
C. Waxes
D. Steroids

Explanation:

A. Triacylglycerols: Storage fat.
B. Phospholipids (Correct): Amphipathic molecules forming bilayers.
C. Waxes: Protective coatings.
D. Steroids: Regulatory molecules, minor membrane components.

Q36.

Steroid hormones are derived from:
A. Proteins
B. Cholesterol ✅
C. Nucleotides
D. Carbohydrates

Explanation:

**A. Proteins = peptide hormones.
B. Cholesterol (Correct): Precursor for steroid hormones (testosterone, estrogen, cortisol).
**C. Nucleotides: not precursor of steroids.
**D. Carbohydrates: not precursors.

Q37.

Which vitamin is fat-soluble?
A. Vitamin B12
B. Vitamin C
C. Vitamin D ✅
D. Vitamin B6

Explanation:

**A. B12 water-soluble.
**B. C water-soluble.
C. Vitamin D (Correct): Fat-soluble, important for calcium metabolism.
**D. B6 water-soluble.

Q38.

Which property is NOT characteristic of enzymes?
A. Specificity to substrates
B. Lowering activation energy
C. Getting consumed in the reaction ✅
D. Accelerating reaction rates

Explanation:

**A. Specificity: true.
**B. Lower activation energy: true.
**C. Correct — enzymes are not consumed, they are catalysts.
**D. Accelerate reaction: true.

Q39.

Which class of enzymes catalyzes the joining of two molecules with ATP hydrolysis?
A. Ligases ✅
B. Hydrolases
C. Transferases
D. Oxidoreductases

Explanation:

A. Ligases (Correct): Catalyze bond formation with ATP breakdown (e.g., DNA ligase).
**B. Hydrolases: break bonds with water.
**C. Transferases: transfer functional groups.
**D. Oxidoreductases: electron transfer.

Q40.

Enzyme activity is influenced by all EXCEPT:
A. Temperature
B. pH
C. Substrate concentration
D. DNA replication ✅

Explanation:

**A. Temp influences folding.
**B. pH influences ionization.
**C. Substrate conc influences rate until Vmax.
**D. DNA replication: not related to enzyme activity.

Q41.

Which of the following is an example of a fibrous protein?
A. Hemoglobin
B. Collagen ✅
C. Enzyme amylase
D. Insulin

Explanation:

**A. Hemoglobin: globular.
B. Collagen (Correct): Fibrous structural protein in connective tissue.
**C. Amylase: globular enzyme.
**D. Insulin: globular hormone.

Q42.

Which is NOT a lipid-derived molecule?
A. Steroids
B. Waxes
C. Cellulose ✅
D. Triacylglycerols

Explanation:

**A. Steroids: lipids.
**B. Waxes: lipids.
C. Cellulose (Correct): Carbohydrate (polysaccharide).
**D. Triacylglycerols: lipids.

Q43.

Which of the following polysaccharides is branched?
A. Amylose
B. Amylopectin ✅
C. Cellulose
D. Chitin

Explanation:

**A. Amylose: unbranched starch.
B. Amylopectin (Correct): Branched (α-1,6 linkages).
**C. Cellulose: linear β-1,4.
**D. Chitin: linear β-1,4 with N-acetylglucosamine.

Q44.

Which amino acid contains sulfur?
A. Alanine
B. Cysteine ✅
C. Glycine
D. Serine

Explanation:

**A. Alanine: no sulfur.
B. Cysteine (Correct): Contains sulfhydryl group (-SH).
**C. Glycine: smallest amino acid, no sulfur.
**D. Serine: contains hydroxyl, not sulfur.

Q45.

Which enzyme class hydrolyzes peptide bonds?
A. Lipases
B. Proteases ✅
C. Nucleases
D. Transferases

Explanation:

**A. Lipases: hydrolyze fats.
B. Proteases (Correct): Hydrolyze proteins into peptides/amino acids.
**C. Nucleases: hydrolyze nucleic acids.
**D. Transferases: transfer groups.

Q46.

Which protein is an oxygen-storage molecule in muscle?
A. Hemoglobin
B. Myoglobin ✅
C. Collagen
D. Keratin

Explanation:

**A. Hemoglobin: oxygen transport in blood.
B. Myoglobin (Correct): Stores oxygen in muscle tissue.
**C. Collagen: structural.
**D. Keratin: hair, nails.

Q47.

Which enzyme converts sucrose into glucose and fructose?
A. Sucrase ✅
B. Amylase
C. Lactase
D. Lipase

Explanation:

A. Sucrase (Correct): Splits sucrose into glucose + fructose.
**B. Amylase: starch hydrolysis.
**C. Lactase: lactose hydrolysis.
**D. Lipase: fat hydrolysis.

Q48.

Which protein transports oxygen in blood?
A. Hemoglobin ✅
B. Myosin
C. Insulin
D. Collagen

Explanation:

A. Hemoglobin (Correct): Iron-containing protein in RBCs binds oxygen.
**B. Myosin: motor protein.
**C. Insulin: hormone.
**D. Collagen: structural.

Q49.

Which polysaccharide forms fungal cell walls?
A. Cellulose
B. Chitin ✅
C. Glycogen
D. Amylose

Explanation:

**A. Cellulose: plant walls.
B. Chitin (Correct): Polysaccharide with N-acetylglucosamine units.
**C. Glycogen: storage in animals.
**D. Amylose: starch in plants.

Q50.

Which enzyme class transfers phosphate groups?
A. Hydrolases
B. Transferases (kinases) ✅
C. Oxidoreductases
D. Ligases

Explanation:

**A. Hydrolases: cleavage using water.
B. Transferases (Correct): Kinases transfer phosphate groups.
**C. Oxidoreductases: redox.
**D. Ligases: joining molecules.

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Part 2 — Proteins, Carbohydrates, Lipids & Enzyme Classifications (Q26–50)