Multiple Choice Questions (MCQs) and Explanations
Question 1: Which of the following is a monosaccharide?
(A) Sucrose
(B) Maltose
(C) Lactose
(D) Fructose
Correct Answer: (D)
Reasoning: Fructose is a monosaccharide (a ketose), meaning it cannot be hydrolyzed into simpler carbohydrate units. Sucrose, maltose, and lactose are disaccharides.
Question 2: Which of the following is a non-reducing sugar?
(A) Glucose
(B) Fructose
(C) Maltose
(D) Sucrose
Correct Answer: (D)
Reasoning: Sucrose is a non-reducing sugar because the glycosidic linkage is formed between C1 of glucose and C2 of fructose, effectively involving both the aldehyde group of glucose and the ketone group of fructose, leaving no free reducing groups. All monosaccharides and maltose are reducing sugars.
Question 3: Proteins are polymers of:
(A) Monosaccharides
(B) Amino acids
(C) Nucleotides
(D) Fatty acids
Correct Answer: (B)
Reasoning: Proteins are large complex molecules formed by the polymerization of α-amino acids linked by peptide bonds.
Question 4: The linkage present in starch and cellulose is:
(A) Peptide linkage
(B) Glycosidic linkage
(C) Phosphodiester linkage
(D) Ester linkage
Correct Answer: (B)
Reasoning: Starch and cellulose are polysaccharides, meaning they are polymers of monosaccharide units linked together by glycosidic bonds. Peptide bonds are in proteins, phosphodiester in nucleic acids, and ester in lipids.
Question 5: Which of the following diseases is caused by the deficiency of Vitamin D?
(A) Scurvy
(B) Night blindness
(C) Rickets
(D) Beri-beri
Correct Answer: (C)
Reasoning: Rickets (in children) and osteomalacia (in adults) are caused by the deficiency of Vitamin D, which is essential for calcium and phosphorus absorption. Scurvy (Vitamin C), night blindness (Vitamin A), and Beri-beri (Vitamin B1) are deficiencies of other vitamins.
Question 6: The two polynucleotide strands in DNA are held together by:
(A) Covalent bonds
(B) Ionic bonds
(C) Hydrogen bonds
(D) Disulfide bonds
Correct Answer: (C)
Reasoning: The double helix structure of DNA is maintained by hydrogen bonds formed between complementary nitrogenous bases (A-T and G-C) on the two strands.
Question 7: The process of denaturation of proteins involves the loss of their:
(A) Primary structure
(B) Secondary and tertiary structures
(C) Peptide bonds
(D) All of the above
Correct Answer: (B)
Reasoning: Denaturation disrupts the higher-level structures (secondary, tertiary, and quaternary) of proteins, typically due to the breaking of hydrogen bonds and other weak interactions, but it usually does not break the primary structure (peptide bonds).
Question 8: Which base is found in RNA but not in DNA?
(A) Adenine
(B) Guanine
(C) Cytosine
(D) Uracil
Correct Answer: (D)
Reasoning: Uracil (U) is a pyrimidine base found only in RNA, where it replaces Thymine (T), which is found only in DNA.
Question 9: The amino acids that cannot be synthesized in the body and must be supplied through diet are called:
(A) Non-essential amino acids
(B) Essential amino acids
(C) Neutral amino acids
(D) Sulphur-containing amino acids
Correct Answer: (B)
Reasoning: Essential amino acids are those that the human body cannot synthesize on its own and therefore must be obtained from dietary sources. Non-essential amino acids can be synthesized by the body.
Question 10: Glycogen is a polymer of:
(A) Fructose
(B) Galactose
(C) α-D-glucose
(D) β-D-glucose
Correct Answer: (C)
Reasoning: Glycogen is the storage polysaccharide in animals and is a highly branched polymer of α-D-glucose units, similar to amylopectin in starch. Cellulose is a polymer of β-D-glucose.
Question 11: The sugar present in DNA is:
(A) Ribose
(B) Glucose
(C) Fructose
(D) 2-Deoxyribose
Correct Answer: (D)
Reasoning: DNA contains 2-deoxyribose sugar, which lacks an oxygen atom at the 2′ carbon position compared to ribose. Ribose is the sugar found in RNA.
Question 12: Which type of protein provides structural support to organisms?
(A) Globular proteins
(B) Fibrous proteins
(C) Enzymes
(D) Hormones
Correct Answer: (B)
Reasoning: Fibrous proteins (like keratin, collagen, myosin) are elongated, thread-like molecules that are typically insoluble in water and provide strength and structural support. Globular proteins are usually involved in metabolic functions.
Question 13: What is the specific term for the pH at which an amino acid has no net charge and exists as a zwitter ion?
(A) Neutral pH
(B) Optimal pH
(C) Isoelectric point
(D) Equivalence point
Correct Answer: (C)
Reasoning: The isoelectric point (pI) is the specific pH value at which an amino acid exists predominantly as a zwitter ion, with an equal number of positive and negative charges, resulting in a net charge of zero.
Question 14: Which of the following is an example of a fat-soluble vitamin?
(A) Vitamin B1
(B) Vitamin C
(C) Vitamin K
(D) Vitamin B12
Correct Answer: (C)
Reasoning: Vitamins A, D, E, and K are fat-soluble vitamins, meaning they are absorbed and stored in fat tissues. Vitamin B1, C, and B12 are water-soluble.
Question 15: The basic unit of a nucleic acid is a:
(A) Nucleoside
(B) Base
(C) Phosphate
(D) Nucleotide
Correct Answer: (D)
Reasoning: Nucleic acids are polymers of nucleotides. A nucleotide consists of a sugar, a nitrogenous base, and a phosphate group. A nucleoside is just a sugar and a base.
Question 16: In the double helix structure of DNA, Adenine (A) always pairs with:
(A) Cytosine (C)
(B) Guanine (G)
(C) Thymine (T)
(D) Uracil (U)
Correct Answer: (C)
Reasoning: According to the Watson-Crick base pairing rules in DNA, Adenine (A) forms two hydrogen bonds with Thymine (T). Guanine (G) pairs with Cytosine (C).
Question 17: Which of the following carbohydrate functions as a storage molecule in plants?
(A) Cellulose
(B) Glycogen
(C) Starch
(D) Sucrose
Correct Answer: (C)
Reasoning: Starch is the primary storage polysaccharide in plants. Cellulose is a structural component, glycogen is storage in animals, and sucrose is a transport sugar.
Question 18: Enzymes are essentially:
(A) Carbohydrates
(B) Lipids
(C) Proteins
(D) Nucleic acids
Correct Answer: (C)
Reasoning: All enzymes are proteins (except for a few catalytic RNA molecules called ribozymes). They function as biological catalysts.
Question 19: Which amino acid exists as a zwitter ion in aqueous solution?
(A) All amino acids
(B) Only acidic amino acids
(C) Only basic amino acids
(D) Only neutral amino acids
Correct Answer: (A)
Reasoning: All amino acids, due to the presence of both an acidic carboxyl group and a basic amino group, exist predominantly as zwitter ions (dipolar ions) in aqueous solution at physiological pH.
Question 20: The deficiency of Vitamin C causes:
(A) Beri-beri
(B) Night blindness
(C) Scurvy
(D) Rickets
Correct Answer: (C)
Reasoning: Scurvy, characterized by bleeding gums and joint pain, is caused by a deficiency of Vitamin C (ascorbic acid).
Question 21: What type of glycosidic linkage is present in cellulose?
(A) α-1,4-glycosidic linkage
(B) β-1,4-glycosidic linkage
(C) α-1,6-glycosidic linkage
(D) β-1,6-glycosidic linkage
Correct Answer: (B)
Reasoning: Cellulose is a linear polymer of β-D-glucose units linked by β-1,4-glycosidic bonds. Starch and glycogen primarily have α-linkages.
Question 22: Which of the following is a hormone?
(A) Glucose
(B) Haemoglobin
(C) Insulin
(D) Keratin
Correct Answer: (C)
Reasoning: Insulin is a protein hormone that regulates blood glucose levels. Glucose is a carbohydrate, haemoglobin is a protein (transport), and keratin is a fibrous protein.
Question 23: The overall three-dimensional folding of a polypeptide chain is known as its:
(A) Primary structure
(B) Secondary structure
(C) Tertiary structure
(D) Quaternary structure
Correct Answer: (C)
Reasoning: The tertiary structure refers to the complete 3D conformation of a single polypeptide chain, including the interactions between amino acid side chains.
Question 24: Which of the following is not a pyrimidine base?
(A) Cytosine
(B) Thymine
(C) Uracil
(D) Guanine
Correct Answer: (D)
Reasoning: Guanine is a purine base. Cytosine, Thymine, and Uracil are pyrimidine bases.
Question 25: What happens to an enzyme’s activity if the temperature is significantly increased above its optimal temperature?
(A) Activity increases.
(B) Activity remains constant.
(C) Enzyme undergoes denaturation and loses activity.
(D) Enzyme becomes more stable.
Correct Answer: (C)
Reasoning: Enzymes are proteins, and like other proteins, they are sensitive to temperature. High temperatures cause denaturation, where the enzyme loses its specific 3D shape, including the active site, and thus loses its catalytic activity.
Question 26: The two anomeric forms of glucose are:
(A) D-glucose and L-glucose
(B) Aldehyde form and ketone form
(C) α-D-glucose and β-D-glucose
(D) Open-chain and cyclic forms
Correct Answer: (C)
Reasoning: Anomers are stereoisomers that differ in configuration only at the anomeric carbon (the hemiacetal or hemiketal carbon in the cyclic form). For glucose, these are α-D-glucose and β-D-glucose.
Question 27: The linkage between sugar and phosphate in nucleic acids is called:
(A) Glycosidic linkage
(B) Peptide linkage
(C) Phosphodiester linkage
(D) Ether linkage
Correct Answer: (C)
Reasoning: Nucleotides in a nucleic acid chain are linked by phosphodiester bonds, where a phosphate group forms ester linkages with the hydroxyl groups of two adjacent sugar molecules.
Question 28: Which vitamin is involved in blood clotting?
(A) Vitamin A
(B) Vitamin B
(C) Vitamin C
(D) Vitamin K
Correct Answer: (D)
Reasoning: Vitamin K (phylloquinone) is essential for the synthesis of several blood clotting factors.
Question 29: Sucrose on hydrolysis yields:
(A) Glucose only
(B) Fructose only
(C) Glucose and Fructose
(D) Glucose and Galactose
Correct Answer: (C)
Reasoning: Sucrose is a disaccharide that on hydrolysis (with acid or enzyme invertase) yields one molecule of glucose and one molecule of fructose.
Question 30: Which of the following is a simple protein?
(A) Haemoglobin (contains heme group)
(B) Glycoprotein (contains carbohydrate)
(C) Albumin (e.g., egg albumin)
(D) Lipoprotein (contains lipid)
Correct Answer: (C)
Reasoning: Simple proteins yield only amino acids upon hydrolysis. Albumin is an example. Conjugated proteins like haemoglobin, glycoproteins, and lipoproteins contain a non-protein prosthetic group in addition to amino acids.
Question 31: What type of bonding is primarily responsible for the α-helix and β-pleated sheet structures in proteins?
(A) Covalent bonds
(B) Ionic bonds
(C) Hydrogen bonds
(D) Disulfide bonds
Correct Answer: (C)
Reasoning: The secondary structures of proteins (α-helix and β-pleated sheet) are stabilized by hydrogen bonds formed between the carbonyl oxygen and amide hydrogen atoms of the polypeptide backbone.
Question 32: Mutarotation is observed in:
(A) Starch
(B) Cellulose
(C) Sucrose
(D) Glucose
Correct Answer: (D)
Reasoning: Mutarotation is the change in optical rotation observed when a pure anomer of a monosaccharide (like α-D-glucose or β-D-glucose) is dissolved in water, slowly converting into an equilibrium mixture of both anomers and the open-chain form. Sucrose is non-reducing and does not show mutarotation.
Question 33: Which vitamin deficiency causes pernicious anemia?
(A) Vitamin B1
(B) Vitamin B6
(C) Vitamin B12
(D) Vitamin C
Correct Answer: (C)
Reasoning: Pernicious anemia is a severe form of anemia caused by a deficiency of Vitamin B12 (cyanocobalamin), which is crucial for red blood cell formation and nervous system function.
Question 34: In DNA, the purine bases are:
(A) Adenine and Cytosine
(B) Guanine and Thymine
(C) Adenine and Guanine
(D) Cytosine and Thymine
Correct Answer: (C)
Reasoning: The purine bases are Adenine (A) and Guanine (G). Cytosine, Thymine, and Uracil are pyrimidine bases.
Question 35: The functional group present in an aldose is:
(A) Ketone
(B) Aldehyde
(C) Carboxyl
(D) Hydroxyl
Correct Answer: (B)
Reasoning: An aldose is a monosaccharide containing an aldehyde (−CHO) functional group.
Question 36: A protein hormone that regulates blood sugar levels is:
(A) Adrenaline
(B) Thyroxine
(C) Insulin
(D) Estrogen
Correct Answer: (C)
Reasoning: Insulin is a peptide hormone produced by the pancreas that lowers blood glucose levels. Adrenaline and Thyroxine are amino acid derivatives, and Estrogen is a steroid hormone.
Question 37: The process of unwinding the double helix of DNA is called:
(A) Denaturation
(B) Renaturation
(C) Replication
(D) Transcription
Correct Answer: (A)
Reasoning: In the context of DNA, denaturation refers to the unwinding and separation of the two complementary strands of the double helix, typically by heat or changes in pH, breaking the hydrogen bonds between base pairs.
Question 38: Which of the following carbohydrates is a highly branched polymer of α-D-glucose and serves as storage in animals?
(A) Starch
(B) Cellulose
(C) Glycogen
(D) Lactose
Correct Answer: (C)
Reasoning: Glycogen is known as “animal starch” and is a highly branched polymer of α-D-glucose, serving as the primary energy storage in animals.
Question 39: The phenomenon where the enzyme’s active site changes shape slightly to fit the substrate more perfectly is described by the:
(A) Lock and Key Model
(B) Induced Fit Model
(C) Transition State Model
(D) Michaelis-Menten Model
Correct Answer: (B)
Reasoning: The Induced Fit Model proposes that the enzyme’s active site is flexible and can undergo a conformational change upon substrate binding to achieve a more precise fit. The Lock and Key model suggests a rigid fit.
Question 40: Which vitamin deficiency causes night blindness?
(A) Vitamin B2
(B) Vitamin A
(C) Vitamin D
(D) Vitamin E
Correct Answer: (B)
Reasoning: Night blindness (nyctalopia) is a common symptom of Vitamin A (Retinol) deficiency, as Vitamin A is crucial for vision.