🧪 Chemistry · Class 12 · NEET & JEE
Biomolecules - Practice Questions with Answers 75 free MCQs on Biomolecules, each with its own worked answer and explanation. The chemistry of life: carbohydrates, proteins, lipids, nucleic acids, enzymes, and vitamins. Understand their structures, classification, and biological functions. Highly relevant for NEET and Class 12 board exams.
Take the timed Biomolecules chapterwise test → 75 practice questions on Biomolecules , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Biomolecules notes .
Peptide Bond Formation (Condensation) H₂N-CH(R₁)-C(=O) OH Amino acid 1 + H NH-CH(R₂)-COOH Amino acid 2 → H₂N-CH(R₁)-CO -NH -CH(R₂)-COOH Dipeptide + H₂O The -OH (from acid 1) and -H (from amine 2) combine to release water, forming the -CO-NH- peptide bond Two amino acids join via a condensation reaction: the carboxyl -OH of one and an amine -H of the other are eliminated as water, leaving a peptide bond (-CO-NH-) linking them into a dipeptide; repeating this builds a full protein chain.
Easy - 25 questions Q3.
Glucose on reduction with sodium amalgam and water gives:
A Gluconic acidB Saccharic acidC SorbitolD Glucose oximeShow answer & explanation →
Q6.
Which biomolecule is the primary source of energy for living organisms?
A CarbohydratesB ProteinsC LipidsD Nucleic acidsShow answer & explanation →
Q8.
Which bond joins amino acids in proteins?
A Peptide bondB Glycosidic bondC Phosphodiester bondD Hydrogen bondShow answer & explanation →
Q14.
The double helix structure of DNA was proposed by:
A Watson and CrickB Pauling and CoreyC ChargaffD Rosalind FranklinShow answer & explanation →
Q17.
Which vitamin is produced by the body when exposed to sunlight?
A Vitamin DB Vitamin CC Vitamin AD Vitamin B12Show answer & explanation →
Q18.
Sucrose is a disaccharide made of:
A Glucose and fructoseB Glucose and glucoseC Glucose and galactoseD Fructose and galactoseShow answer & explanation →
Q19.
Which type of RNA carries amino acids to the ribosome during protein synthesis?
A tRNAB mRNAC rRNAD snRNAShow answer & explanation →
Q21.
Which element is present in proteins but NOT in carbohydrates or fats?
A NitrogenB CarbonC HydrogenD OxygenShow answer & explanation →
Q23.
Cellulose is a structural component of:
A Plant cell wallsB Animal cell membranesC Animal bonesD Bacterial cell wallsShow answer & explanation →
Q25.
Haemoglobin is a protein that contains which metal ion?
A Iron (Fe<sup>2+</sup>)B Copper (Cu<sup>2+</sup>)C Zinc (Zn<sup>2+</sup>)D Magnesium (Mg<sup>2+</sup>)Show answer & explanation →
Medium - 25 questions Q26.
Glucose reacts with hydroxylamine (NH<sub>2</sub>OH) to form a glucose oxime. This confirms the presence of a:
A Hydroxyl groupB Carbonyl groupC Carboxyl groupD Amino groupShow answer & explanation →
Q27.
Glucose pentaacetate does not react with hydroxylamine. This indicates that glucose:
A Contains five hydroxyl groups in a ringB Has a branched carbon skeleton in solutionC Exists as a cyclic hemiacetal lacking free CHOD Is a non-reducing disaccharide in the solid stateShow answer & explanation →
Q29.
The branch points in amylopectin and glycogen are formed by which glycosidic linkage?
A C1-C6 (alpha-1,6)B C1-C4 (alpha-1,4)C C1-C4 (beta-1,4)D C1-C6 (beta-1,6)Show answer & explanation →
Q30.
Essential amino acids are those which:
A Are synthesised in the body in excessB Cannot be made in the body and come from dietC Contain a sulphur atom in the side chainD Are optically inactive in aqueous solutionShow answer & explanation →
Q31.
What is the primary structure of a protein?
A Sequence of amino acids in the polypeptide chainB The regular coiling pattern formed by hydrogen bonds along the backboneC The regular pleated pattern formed between adjacent backbone strandsD The overall compact 3D shape stabilised by multiple bond typesShow answer & explanation →
Q32.
Which forces stabilise the alpha-helix secondary structure of proteins?
A Hydrogen bonds between NH and C=O groupsB Covalent disulfide bonds between cysteine side chainsC Ionic bonds between charged side chain residuesD Weak van der Waals forces between nonpolar side chainsShow answer & explanation →
Q33.
The Chargaff rule states that in DNA:
A [A]=[T] and [G]=[C]B [A]=[G] and [T]=[C]C [A]+[T]=[G]+[C]D All bases are equalShow answer & explanation →
Q34.
What type of bond connects nucleotides in a DNA strand?
A Phosphodiester bondB Glycosidic bondC Peptide bondD Hydrogen bondShow answer & explanation →
Q37.
The region of an enzyme where substrate binds is called the:
A Active siteB Allosteric siteC Coenzyme binding siteD Inhibitor siteShow answer & explanation →
Q38.
Reducing sugars give a positive test with:
A Fehling's solutionB Iodine solutionC NinhydrinD Biuret reagentShow answer & explanation →
Q41.
Glycine is the simplest amino acid because:
A Its R group is just a hydrogen atomB It has no carboxyl group in standard practiceC It has no amino group under most conditions encounteredD It is non-polar as frequently observed in practiceShow answer & explanation →
Q42.
Which amino acids form disulfide bridges in proteins?
A Two cysteine residuesB Two glycine residuesC Lysine and aspartateD Serine and threonineShow answer & explanation →
Q43.
Denaturation of a protein involves:
A Loss of 3D structure while primary structure remains intactB Hydrolysis of the peptide bonds linking adjacent amino acidsC Formation of new covalent bonds within the polypeptide chainD Reduction of the protein's peptide carbonyl groupsShow answer & explanation →
Q44.
Maltose is a disaccharide formed by:
A Two glucose units linked by alpha 1,4-glycosidic bondB Glucose and fructose joined by an alpha,beta 1,2-glycosidic bondC Glucose and galactose joined by a beta 1,4-glycosidic bondD Two fructose units joined by a beta 2,1-glycosidic bondShow answer & explanation →
Q46.
What is the role of NAD+ in metabolism?
A Electron/hydrogen carrier in oxidation-reduction reactionsB A phospholipid component of the cell membrane bilayerC A high-energy phosphate storage molecule like ATPD An enzyme that excises damaged bases from DNAShow answer & explanation →
Q47.
Which part of the amino acid determines its properties?
A R group (side chain)B Amino groupC Carboxyl groupD Alpha carbonShow answer & explanation →
Q48.
Lipids are not polymers because:
A They are joined by ester bonds not polymerised like polysaccharides; no repeating monomer unitsB Their fatty acid chains contain no carbon-carbon bonds capable of linking units togetherC They are completely insoluble in water and in every organic solvent testedD Their individual molecular weight is far too low to ever form a repeating chainShow answer & explanation →
Q49.
The Haworth projection represents:
A Cyclic form of carbohydratesB Amino acid structure in many documented casesC DNA base pairing according to conventional understandingD Lipid bilayer in routine practiceShow answer & explanation →
Q50.
Insulin is a hormone that is chemically a:
A Protein (polypeptide)B Lipid overall in most casesC Carbohydrate under typical conditionsD Nucleic acid according to standard textbooksShow answer & explanation →
Hard - 25 questions Q51.
Sanger reagent (2,4-dinitrofluorobenzene) is used in protein analysis to identify the:
A C-terminal amino acidB Disulphide bridge positionC N-terminal amino acidD Total number of residuesShow answer & explanation →
Q52.
In monosaccharides, the D or L configuration is assigned on the basis of the:
A Number of hydroxyl groups presentB Direction of rotation of polarised lightC Position of the carbonyl in the chainD Configuration of the lowest chiral carbonShow answer & explanation →
Q53.
Mutarotation of glucose is best explained as the:
A Interconversion of the alpha- and beta-anomersB Oxidation of glucose to gluconic acidC Rotation of the whole molecule in waterD Formation of an osazone derivativeShow answer & explanation →
Q54.
In protein synthesis, a sequence of three bases on mRNA that specifies one amino acid is called a:
A AnticodonB CodonC OperonD CistronShow answer & explanation →
Q55.
Deficiency of vitamin B<sub>12</sub> in humans causes:
A Night blindnessB Bleeding gumsC Pernicious anaemiaD Poor blood clottingShow answer & explanation →
Q57.
The anomeric carbon in glucose is:
A C-1 (the aldehyde carbon in the open chain)B C-2, the carbon bearing the secondary hydroxyl groupC C-3, the central carbon of the pyranose ringD C-6, the primary alcohol carbon outside the ringShow answer & explanation →
Q58.
Alpha-D-glucose and beta-D-glucose are:
A Anomers (differ at the anomeric carbon)B Enantiomers, being exact mirror images of each otherC Diastereomers differing in configuration at every chiral centreD Constitutional isomers with different connectivity of atomsShow answer & explanation →
Q59.
In the beta-pleated sheet, adjacent polypeptide chains are held by:
A Intermolecular hydrogen bonds between backbone groupsB Disulfide bonds formed between adjacent cysteine residuesC Ionic bonds between oppositely charged side chainsD Hydrophobic interactions between nonpolar side chainsShow answer & explanation →
Q60.
Mutation in DNA results from:
A Change in base sequenceB Change in sugarC Loss of phosphateD DenaturationShow answer & explanation →
Q61.
Which enzyme catalyses the formation of peptide bonds during translation?
A Peptidyl transferase (part of the ribosome)B DNA polymerase, which extends a nucleotide strand during replicationC RNA polymerase, which synthesises mRNA from a DNA templateD Topoisomerase, which relieves supercoiling tension in DNAShow answer & explanation →
Q62.
What is the isoelectric point (pI) of an amino acid?
A The pH at which the amino acid has no net charge (zwitterion)B The pH at which the amino acid is fully protonated on both endsC The pKa value of the carboxyl group aloneD The pH at which the amino acid shows maximum aqueous solubilityShow answer & explanation →
Q63.
Nucleoside differs from nucleotide in that nucleoside:
A Lacks the phosphate groupB Lacks the sugar according to most researchersC Lacks the base in the majority of cases studiedD Is a polymer as widely reportedShow answer & explanation →
Q65.
The glycosidic bond in cellulose is:
A Beta-1,4 glycosidic bondB Alpha-1,4 glycosidic bondC Alpha-1,6 glycosidic bondD Beta-1,6 glycosidic bondShow answer & explanation →
Q67.
Competitive inhibitors of enzymes:
A Bind to the active site and compete with substrateB Bind irreversibly and permanently inactivate the enzymeC Unfold the enzyme's tertiary structure, destroying activityD Raise the maximum velocity Vmax while leaving Km unchangedShow answer & explanation →
Q68.
Zwitterion formation in amino acids occurs because:
A The amino group accepts a proton from the carboxyl group intramolecularlyB An external acid molecule donates a proton to the amino group in standard practiceC The hydrophobic R group ionises under physiological pH under most conditions encounteredD Surrounding water molecules donate protons to both ends as frequently observed in practiceShow answer & explanation →
Q69.
Which of the following correctly describes the B-form of DNA?
A Right-handed double helix, 10 base pairs per turn, major and minor groovesB Left-handed double helix with 12 base pairs per turn (Z-DNA form) in many documented casesC A single-stranded structure lacking complementary base pairing according to conventional understandingD A right-handed helix with 14 base pairs per turn in routine practiceShow answer & explanation →
Q70.
Enzyme activity is maximum at the optimum temperature because:
A Activation energy is minimum and protein structure is intactB All available substrate molecules are consumed simultaneouslyC Competitive inhibitors are completely absent from the mixtureD The surrounding pH is held exactly neutral at that temperatureShow answer & explanation →
Q72.
Which level of protein structure is disrupted by reducing agents (breaking S-S bonds)?
A Quaternary/Tertiary (disulfide bonds in tertiary structure)B Primary structure, since the amino acid sequence itself is cleavedC Secondary structure, since the alpha-helix hydrogen bonds breakD Primary sequence, since the peptide backbone is hydrolysedShow answer & explanation →
Q73.
The lock-and-key model of enzyme action proposes:
A Substrate shape exactly fits the rigid active siteB The enzyme changes shape on substrate bindingC Multiple substrates share one active siteD The substrate changes shapeShow answer & explanation →
Q74.
Which amino acid is responsible for the UV absorption of proteins at 280 nm?
A Tryptophan (and tyrosine)B Glycine, due to its small aliphatic side chain absorbing stronglyC Alanine, due to its methyl side chain's conjugated systemD Lysine, due to the aromatic character of its amino side chainShow answer & explanation →
Q75.
In gel electrophoresis of DNA, smaller fragments migrate:
A Faster toward the positive electrodeB SlowerC In random directionsD Toward the negative electrodeShow answer & explanation →