🔬 Biology · Class 11 · NEET
Biomolecules - Practice Questions with Answers 75 free MCQs on Biomolecules, each with its own worked answer and explanation. Carbohydrates, proteins, lipids, nucleic acids, and enzyme kinetics. Essential foundation for understanding metabolism.
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 .
Enzyme Kinetics: Rate vs Substrate Concentration [Substrate] Reaction rate Vmax Km ½Vmax Curve flattens at high [S]: ALL enzyme active sites are occupied (saturation) As substrate concentration rises, reaction rate increases steeply at first, then plateaus at Vmax once every enzyme molecule is working at full capacity; Km is the substrate concentration giving half-maximal rate, and a LOWER Km means the enzyme reaches that rate with less substrate (higher affinity).
Easy - 25 questions Q2.
A nucleotide is made of a nitrogenous base, a pentose sugar and:
A A fatty acidB A phosphate groupC An amino acidD A metal ionShow answer & explanation →
Q8.
What is the primary function of enzymes?
A Store energyB Catalyze chemical reactionsC Transport oxygenD Build cell membranesShow answer & explanation →
Q10.
What type of bond links amino acids in a protein chain?
A Ionic bondB Glycosidic bondC Peptide bondD Phosphodiester bondShow answer & explanation →
Q20.
The region on an enzyme where the substrate binds is called the
A Allosteric siteB Active siteC Binding domainD Catalytic cleftShow answer & explanation →
Q21.
Which class of biomolecules includes fats, oils, and waxes?
A ProteinsB CarbohydratesC LipidsD Nucleic acidsShow answer & explanation →
Q24.
Which vitamin is required as a coenzyme in many metabolic reactions?
A Vitamin A, for vision and skin healthB Vitamin B complexC Vitamin C, for collagen synthesisD Vitamin D, for calcium absorptionShow answer & explanation →
Medium - 25 questions Q27.
A nucleoside differs from a nucleotide in that a nucleoside lacks the:
A Nitrogen baseB Pentose sugarC Phosphate groupD Hydrogen bondShow answer & explanation →
Q28.
A triglyceride (fat) is formed from one molecule of glycerol joined to:
A One amino acidB Two phosphate groupsC One nucleotide baseD Three fatty acidsShow answer & explanation →
Q29.
An enzyme speeds up a reaction mainly by:
A Lowering the activation energyB Raising the temperature neededC Adding energy to the reactantsD Shifting the equilibrium pointShow answer & explanation →
Q30.
A complete, catalytically active enzyme made of an apoenzyme plus its cofactor is called a:
A CoenzymeB HoloenzymeC ZymogenD IsoenzymeShow answer & explanation →
Q32.
The Michaelis constant (Km) of an enzyme represents
A The maximum reaction rate achieved when the enzyme is fully saturatedB Substrate concentration at half VmaxC The total enzyme concentration present within the reaction mixtureD The pH value at which the enzyme shows peak catalytic activityShow answer & explanation →
Q33.
A competitive inhibitor affects enzyme kinetics by
A Decreasing Vmax onlyB Increasing Km onlyC Decreasing both Km and VmaxD Increasing both Km and VmaxShow answer & explanation →
Q34.
Denaturation of a protein involves
A Hydrolytic cleavage of the covalent peptide bonds linking amino acid residuesB Loss of 3D structure without breaking peptide bondsC Condensation reactions forming additional peptide bonds within the chainD De novo synthesis of new amino acid monomers from precursor moleculesShow answer & explanation →
Q35.
Which of the following is the most abundant organic compound on Earth?
A GlucoseB StarchC CelluloseD GlycogenShow answer & explanation →
Q36.
An enzyme that requires a metal ion cofactor for activity is called
A ApoenzymeB HoloenzymeC CoenzymeD ProenzymeShow answer & explanation →
Q37.
Lactose is composed of which two monosaccharides?
A Glucose and fructoseB Glucose and galactoseC Galactose and fructoseD Two glucose unitsShow answer & explanation →
Q39.
Which levels of protein structure involve interactions between R groups of amino acids?
A Primary mainlyB Secondary mainlyC Tertiary and quaternaryD Primary and secondaryShow answer & explanation →
Q40.
What is a zymogen?
A An active enzyme ready to catalyze reactionsB An inactive enzyme precursorC A type of coenzyme assisting enzyme functionD A regulatory protein controlling gene expressionShow answer & explanation →
Q41.
Sucrose is formed by joining glucose and fructose through which bond?
A Alpha-1,4-glycosidicB Beta-1,4-glycosidicC Alpha-1,2-glycosidicD Beta-1,6-glycosidicShow answer & explanation →
Q42.
Fat-soluble vitamins are stored in body fat and liver. Which set is correct?
A A, B, C, DB A, D, E, KC B, C, E, KD A, C, D, EShow answer & explanation →
Q43.
The induced fit model of enzyme action proposes that
A The enzyme shape is rigid and does not changeB The active site changes shape to better fit the substrateC The substrate changes shape to fit the active siteD Enzyme and substrate have identical shapesShow answer & explanation →
Q44.
Which bond links nucleotides together in a DNA strand?
A Peptide bondB Glycosidic bondC Phosphodiester bondD Hydrogen bondShow answer & explanation →
Q45.
Which amino acid contains a sulfur atom and forms disulfide bonds?
A GlycineB AlanineC CysteineD TyrosineShow answer & explanation →
Q46.
What is the difference between alpha-glucose and beta-glucose?
A Number of carbon atomsB Position of -OH group at C1C Number of oxygen atomsD Type of glycosidic bond onlyShow answer & explanation →
Q47.
The process of converting excess amino acids into glucose is called
A Gluconeogenesis from pyruvate generated solely during anaerobic glycolysisB Glycogenolysis, the breakdown of stored liver glycogen into free glucoseC Transamination, the transfer of an amino group between two keto acidsD Deamination followed by gluconeogenesisShow answer & explanation →
Q50.
What is the secondary structure of a protein stabilized by?
A Disulfide bonds linking cysteine residuesB Ionic interactions between charged side chainsC Hydrogen bonds between backbone atomsD Hydrophobic interactions burying nonpolar residuesShow answer & explanation →
Hard - 25 questions Q51.
In the Watson-Crick B-DNA model, one complete turn of the double helix spans about:
A 0.34 nm, covering one base pairB 2.0 nm, covering five base pairsC 3.4 nm, covering ten base pairsD 34 nm, covering thirty base pairsShow answer & explanation →
Q52.
Alkaloids, terpenoids and essential oils produced by plants are examples of:
A Primary metabolitesB Inorganic ionsC Structural macromoleculesD Secondary metabolitesShow answer & explanation →
Q54.
Amino acids are amphoteric because, in aqueous solution, they mostly exist as:
A Neutral non-polar moleculesB Doubly charged zwitterionsC Purely negative ionsD Purely positive ionsShow answer & explanation →
Q55.
Biomacromolecules of the acid-insoluble fraction are distinguished from small biomolecules by having molecular weights:
A Below about 18 daltonsB Of roughly 100 daltonsC Above about 1000 daltonsD Of exactly 342 daltonsShow answer & explanation →
Q56.
A non-competitive inhibitor affects enzyme kinetics by
A Increasing Km and decreasing VmaxB Decreasing Vmax without changing KmC Increasing Vmax without changing KmD Decreasing Km onlyShow answer & explanation →
Q57.
The Bohr effect explains why hemoglobin releases O<sub>2</sub> in metabolically active tissues. Which factors cause this?
A High O<sub>2</sub> and low CO<sub>2</sub>B Low CO<sub>2</sub> and high pHC High CO<sub>2</sub> and low pHD High pH and low temperatureShow answer & explanation →
Q58.
In enzyme kinetics, which plot linearizes the Michaelis-Menten equation?
A Arrhenius plotB Lineweaver-Burk plotC Ramachandran plotD Henderson-Hasselbalch plotShow answer & explanation →
Q59.
Positive cooperativity in hemoglobin means
A The first O<sub>2</sub> molecule binds with the highest overall affinityB Binding of one O<sub>2</sub> increases affinity for subsequent O<sub>2</sub> moleculesC Each subunit binds O<sub>2</sub> fully independently of the othersD O<sub>2</sub> binding affinity decreases with each subsequent molecule boundShow answer & explanation →
Q60.
What is the role of ubiquitin in protein quality control?
A It directly refolds misfolded polypeptides back into their native conformationB It tags damaged proteins for proteasomal degradationC It functions as a molecular chaperone that shields nascent chains from aggregationD It binds ribosomes to halt ongoing translation of damaged mRNA transcriptsShow answer & explanation →
Q61.
Which property explains why fats yield more energy per gram than carbohydrates?
A Fats contain a greater proportion of oxygen atoms per carbon skeletonB Fats are more highly reduced (more C-H bonds)C Fats are built from longer unbranched carbon chains than glucose polymersD Fats are insoluble in water and stored within dedicated adipocyte vacuolesShow answer & explanation →
Q63.
In protein synthesis, what is the role of the 5' cap and poly-A tail on mRNA?
A They encode the start and stop codons recognized during translationB They protect mRNA from degradation and aid ribosome bindingC They are excised together with introns during the spliceosome reactionD They serve solely as the signal required for nuclear pore exportShow answer & explanation →
Q64.
What distinguishes NAD+ from NADP+ functionally?
A NAD+ functions mainly within the nucleus during DNA repair reactions overallB NADP+ is mainly used in anabolic reactions while NAD+ is in catabolic reactionsC NAD+ carries two additional electrons per molecule compared to NADP+D NADP+ is confined largely to the mitochondrial matrix compartmentShow answer & explanation →
Q65.
Which enzyme catalyzes the rate-limiting step of glycolysis?
A AldolaseB Phosphoglucose isomeraseC Phosphofructokinase-1D Pyruvate kinaseShow answer & explanation →
Q66.
What is the significance of the omega-3 and omega-6 fatty acids being called essential?
A They yield more usable ATP per gram than any other dietary fatty acidB Humans cannot synthesize them and must obtain them from dietC They represent a relatively minor class of unsaturated fatty acids found in the human dietD They are biologically required mainly during the early childhood growth periodShow answer & explanation →
Q67.
Feedback inhibition in a metabolic pathway means
A The first enzyme in the sequence directly activates the formation of the final productB The final product inhibits an early enzyme in its own synthesisC Excess substrate itself binds and inhibits the enzyme that processes itD Reaction products universally enhance the activity of the enzymes that made themShow answer & explanation →
Q68.
In gel electrophoresis, DNA fragments are separated based on
A Net electrical charge alone, since all DNA fragments carry identical massB Absolute molecular mass alone, independent of fragment length or chargeC Size (smaller fragments travel farther)D Specific nucleotide sequence composition recognized by the gel matrixShow answer & explanation →
Q69.
Wobble base pairing in translation refers to
A Mispairing that sometimes occurs between the mRNA transcript and the template DNA strand in many documented casesB Flexible base pairing at the third codon position allowing one tRNA to recognize multiple codonsC Largely random, non-specific binding occurring between any codon and any anticodon according to conventional understandingD Lateral sliding of the ribosome along the mRNA strand without proper translocation in routine practiceShow answer & explanation →
Q70.
What makes telomerase important for cell immortality?
A It repairs double-strand breaks scattered throughout the chromosome armsB It adds telomeric repeats to chromosome ends, preventing shorteningC It deposits methyl marks onto histone tails to silence chromosomal regionsD It excises the RNA primers left behind after lagging-strand synthesisShow answer & explanation →
Q71.
What is the role of chaperone proteins?
A Target and degrade misfolded proteins via the ubiquitin-proteasome pathwayB Assist in proper protein folding and prevent aggregationC Actively translocate completed proteins across the ER and mitochondrial membranesD Initiate assembly of the ribosomal subunits at the start codonShow answer & explanation →
Q72.
The turnover number (kcat) of an enzyme represents
A The fixed number of substrate molecules an enzyme requires to become activeB The number of substrate molecules converted per enzyme molecule per secondC The rate at which new enzyme molecules are transcribed and translatedD The rate at which a competitive inhibitor binds the enzyme's active siteShow answer & explanation →
Q73.
Protein denaturation by urea acts by
A Hydrolytically cleaving the covalent peptide backbone of the proteinB Disrupting hydrogen bonds and hydrophobic interactionsC Chelating and stripping essential metal cofactors from the active siteD Covalently adding phosphate groups onto serine and threonine residuesShow answer & explanation →
Q74.
What is the key difference between Type I and Type II restriction enzymes?
A Type I cuts within the recognition site; Type II cuts elsewhereB Type II cuts within or near recognition site; Type I cuts away from itC Type I requires ATP; Type II mainly requires Mg<sup>2+</sup> insteadD Type II works mainly on RNA substrates specificallyShow answer & explanation →
Q75.
The chemical bond that joins two amino acids in a protein is the:
A peptide bondB glycosidic bondC ester bondD simple hydrogen bondShow answer & explanation →