Free NEET Chemistry multiple-choice questions on Proteins. Attempt each question and reveal the answer with a full explanation.
Which of the following amino acids contains a second carboxyl group in its side chain? Glutamic acid Lysine Arginine Threonine Which of the following is an acidic amino acid? Aspartic acid Arginine Histidine Alanine In the structural protein collagen, which amino acid residue appears at every third position in the polypeptide chain to allow the formation of a triple helix? Glycine Proline Hydroxyproline Alanine Most amino acids have the 'S' configuration at the α -carbon. Which of the following is the only chiral proteinogenic amino acid that has an 'R' configuration? Cysteine Serine Isoleucine Threonine The 'antivitamin' present in raw egg white that binds tightly to Biotin (Vitamin H ) and prevents its absorption is: Avidin Ovomucin Conalbumin Lysozyme The Ramachandran plot is used to visualize the allowed conformations of which part of a protein structure? The peptide backbone torsion angles ( ϕ and ψ ) The side-chain rotation angles ( χ ) The hydrogen bonding patterns in the β -sheet The distance between disulfide bridges The correct statement about peptides and proteins is Tertiary structure of proteins has two or more polypeptide subunits Only the proteins having a quaternary structure are biologically active In -pleated sheet structures, peptide chains are held together by intermolecular hydrogen bonds In -helices, the polypeptide chain is twisted into a left-handed screw (helix) through intramolecular hydrogen bonds Insulin and albumin are examples of which type of protein? Globular proteins Fibrous proteins Structural proteins Contractile proteins Which of the following is the most appropriate name for the peptide bond? Amide linkage Ester linkage Ether linkage Glycosidic linkage The primary structure of a protein refers to: The sequence of amino acids The alpha-helix and beta-pleated sheets The overall 3D folding The arrangement of subunits The secondary structure of keratin, the protein found in hair and nails, is primarily: -Helix -Pleated sheet Triple helix Random coil The zwitterionic form of an amino acid has a net charge of: Zero +1 -1 Dependent on the R-group The helical structure of proteins is stabilized by which type of interaction? Hydrogen bonds Disulfide bonds Peptide bonds Ionic bonds The sequence of amino acids in a protein is determined by the sequence of: Nucleotides in DNA Nucleotides in rRNA Carbohydrates in the cell wall Fatty acids in the membrane An enzyme consisting of a protein part and a non-protein part (cofactor) is called a/an: Holoenzyme Apoenzyme Isoenzyme Zymogen Which of the following amino acids is synthesized in the body and thus classified as non-essential? Alanine Valine Leucine Phenylalanine How many peptide bonds are present in a decapeptide molecule? 9 10 11 8 Which of the following hormones is a peptide hormone produced by the pancreas? Insulin Adrenaline Thyroxine Estrogen When a protein is boiled in a strong acid, it hydrolyzes into its constituent amino acids. This process breaks which of the following bonds? Peptide bonds Hydrogen bonds Phosphodiester bonds Glycosidic bonds Which of the following statements is correct regarding the solubility of proteins? Globular proteins are generally soluble in water. Fibrous proteins are highly soluble in water. Globular proteins are insoluble in dilute acids. Fibrous proteins are soluble in aqueous solutions of salts. The basicity of amino acids is primarily due to the presence of which functional group? Amino group Carboxyl group Hydroxyl group Thiol group The 'adapter molecule' that carries amino acids to the ribosome during protein synthesis is: tRNA mRNA rRNA DNA Which of the following amino acids is considered a 'neutral' amino acid? Valine Lysine Aspartic acid Arginine The chemical test used to identify the presence of peptide bonds in a sample is: Biuret test Molisch test Benedict test Barfoed test Which of the following amino acids is basic in nature? Arginine Alanine Serine Tyrosine Which of the following is a 'branched-chain' amino acid? Leucine Glycine Proline Lysine Which functional group participates in disulphide bond formation in proteins :- Thioether Thiol Thioester Thiolactone Which enzyme model suggests that the enzyme's active site is not rigid but changes its shape to fit the substrate perfectly upon binding? Induced Fit Model Lock and Key Model Fluid Mosaic Model Allosteric Model Which of the following is the simplest amino acid - Alanine Asparagine Glycine Tyrosine In a protein molecule various amino acids are linked together by : -glycosidic bond -glycosidic bond peptide bond dative bond Which of the following amino acid is not optically active? Glycine Proline Serine Leucine Which of the following compounds can form a zwitterion? Benzoic acid Acetanilide Aniline Glycine The non-essential amino acid among the following is: Lysine Valine Leucine Alanine Which of the following is a natural polymer? poly (Butadiene-styrene) polybutadiene poly (Butadiene-acrylonitrile) cis-1, 4-polyisoprene Which of the following is a basic amino acid ? Alanine Tyrosine Lysine Serine Which of the following statements about amino acids is incorrect? Most naturally occurring amino acids have D-configuration They are substituted methanes The carbon atom to which amino and carboxyl groups are attached is called -carbon They exist as zwitterions in aqueous solution During denaturation of proteins, which level of structure remains intact? Primary Secondary Tertiary Quaternary Which of the following is an example of a fibrous protein? Keratin Insulin Albumin Hemoglobin Amino acids act as buffers because they can react with both acids and bases. This property is due to their existence as: Zwitterions Enantiomers Anomers Cations only The secondary structure of protein refers to: Regular folding patterns of continuous portions of the polypeptide chain Sequence of amino acids Three-dimensional folding of the whole polypeptide chain Spatial arrangement of two or more polypeptide chains Which amino acid contains a sulfur atom? Cysteine Glycine Alanine Valine Which of the following is an essential amino acid? Valine Glycine Alanine Aspartic acid The melting point and solubility in water of amino acids are generally high because of: Zwitterion formation Presence of amino group Presence of carboxyl group Small size of molecules The isoelectric point of an amino acid is the pH at which: The amino acid exists as a zwitterion and does not migrate in an electric field The amino acid is most soluble in water The amino acid is completely positively charged The amino acid is completely negatively charged In the quaternary structure of proteins, what does the structure represent? The spatial arrangement of multiple polypeptide subunits The linear sequence of amino acids The folding of a single polypeptide chain into a 3D shape The hydrogen bonding between local amino acid residues The direction of the twist in the naturally occurring -helix structure of proteins is: Right-handed Left-handed Alternating Random Insulin, a hormone that regulates blood sugar, consists of two polypeptide chains (A and B) linked together by: Disulfide bonds Hydrogen bonds Ionic bonds Glycosidic bonds The Xanthoproteic test is used for the detection of proteins containing which type of amino acids? Aromatic amino acids Sulfur-containing amino acids Basic amino acids Acidic amino acids In a peptide bond ( R-CONH-R' ), the C-N bond length is shorter than the usual C-N single bond because of: Resonance Inductive effect Hyperconjugation Electromeric effect Which of the following statements about apoenzymes is correct? It is the protein part of a conjugated enzyme It is the non-protein part of a conjugated enzyme It is the complete, active enzyme-cofactor complex It is a metal ion that activates an enzyme The most abundant protein in the whole of the biosphere is: RuBisCO Collagen Insulin Hemoglobin In sickle cell anemia, which amino acid is substituted by Valine at the sixth position of the -globin chain of hemoglobin? Glutamic acid Glycine Lysine Aspartic acid Which of the following amino acids contains a secondary amino group (imino group) in its structure? Proline Alanine Leucine Valine The coagulation of egg white on boiling is an example of protein denaturation. This process involves the disruption of which of the following? Secondary and tertiary structures Primary structure only Peptide bonds Sequence of amino acids The structural protein 'Collagen' is characterized by which unique secondary structure? Triple helix -helix -pleated sheet Random coil Two cysteine molecules can be oxidized to form a covalent bond between their sulfur atoms. This product is called: Cystine Methionine Homocysteine Threonine Which of the following reagents produces 'Ruhemann's Purple' when reacted with amino acids? Ninhydrin Millon's reagent Benedict's solution Molisch reagent The metabolic disorder Phenylketonuria (PKU) is caused by the inability of the body to convert Phenylalanine into which other amino acid? Tyrosine Tryptophan Histidine Proline Which of the following is an essential amino acid containing a hydroxyl group in its side chain? Threonine Serine Tyrosine Alanine In the folding of globular proteins, which type of interaction is primarily responsible for burying non-polar amino acid side chains in the interior of the protein? Hydrophobic interactions Hydrogen bonding Ionic bonding Disulfide linkages An inactive precursor of an enzyme that requires proteolytic cleavage to become active is called a: Zymogen Holoenzyme Cofactor Apoenzyme In a strongly acidic medium ( pH 1.0 ), an amino acid like Alanine exists primarily as: A cation: CH 3CH(NH 3 +)COOH An anion: CH 3CH(NH 2)COO - A zwitterion: CH 3CH(NH 3 +)COO - A neutral molecule: CH 3CH(NH 2)COOH The primary structure of a protein is held together by covalent bonds, whereas the secondary structure is primarily stabilized by: Intramolecular Hydrogen bonding Disulfide linkages Van der Waals forces Electrostatic attractions Which amino acid contains an imidazole ring in its side chain? Histidine Proline Tryptophan Phenylalanine Which of the following is an 'imino acid' rather than a typical -amino acid because its nitrogen is part of a five-membered ring? Proline Leucine Glycine Serine Which of the following statements about denaturation of proteins is CORRECT? It is often irreversible but sometimes can be reversed (renaturation) It always involves the breaking of peptide bonds It increases the biological activity of the protein It results in the formation of a more ordered structure Which of the following forces is NOT involved in maintaining the tertiary structure of proteins? Peptide bonds Hydrophobic interactions Ionic bonds (salt bridges) Disulfide bonds In the -helix structure of proteins, the hydrogen bonds are formed between the carbonyl oxygen of one amino acid residue and the amide hydrogen of the: Fourth residue in the chain Second residue in the chain Third residue in the chain Same residue How many water molecules are removed during the formation of a tripeptide from three amino acids? 2 3 1 4 Which of the following is a prosthetic group often found in conjugated proteins like hemoglobin? Heme Glucose Phosphate Lipid Which of the following interactions is NOT responsible for the tertiary structure of proteins? Phosphodiester bonds Disulfide linkages Hydrophobic interactions Van der Waals forces Which of the following tests is used to detect the presence of proteins? Biuret test Molisch's test Benedict's test Tollen's test What happens when a protein is subjected to a pH change or heat (denaturation)? It loses its biological activity but retains its primary structure. It loses its primary structure. It gains more helical content. The peptide bonds are hydrolyzed. Which of the following amino acids is non-polar (hydrophobic)? Alanine Lysine Aspartic acid Serine The amino acid which has a sulfur-containing side chain and can form disulfide bridges is: Cysteine Methionine Serine Proline When a protein undergoes denaturation, which of the following properties changes significantly? Biological activity Primary structure Sequence of amino acids Covalent bonding Which of the following amino acids contains a phenolic hydroxyl group in its side chain? Tyrosine Serine Threonine Phenylalanine In the process of protein synthesis, the sequence of amino acids is determined by: mRNA tRNA rRNA DNA polymerase The heterocyclic ring present in the amino acid Tryptophan is: Indole Imidazole Pyridine Pyrrole Which of the following amino acids contains a side chain that can be phosphorylated to regulate protein activity? Serine Alanine Valine Leucine Which type of interaction is primarily responsible for the formation of the -pleated sheet structure in proteins? Intermolecular hydrogen bonding Intramolecular hydrogen bonding Disulfide bridges Van der Waals forces The standard pH value of human blood is slightly basic ( 7.35-7.45 ). At this pH, most amino acids exist as: Zwitterions Anions Cations Neutral molecules Which of the following amino acids is optically inactive? Glycine Alanine Valine Leucine Which of the following is a non-essential amino acid that can be synthesized by the body? Tyrosine Lysine Methionine Phenylalanine The structure of the protein 'Myoglobin' is primarily categorized as: Tertiary Primary Secondary Quaternary While most -amino acids react with Ninhydrin to produce a purple-colored compound (Ruhemann's purple), which of the following amino acids produces a characteristic yellow color? Proline Glycine Aspartic acid Histidine Which of the following amino acids contains a 'Guanidino' group in its side chain? Arginine Lysine Histidine Asparagine Which essential amino acid is the biological precursor for the synthesis of Vitamin B 3 (Niacin) in the human body? Tryptophan Tyrosine Phenylalanine Methionine In the isoelectric point ( pI ) calculation for acidic amino acids like Aspartic acid ( pK a1 = 2.1, pK a2 = 9.8, pK aR = 3.9 ), the pI is calculated as the average of: pK a1 and pK aR pK a1 and pK a2 pK a2 and pK aR All three pK a values The -helix structure of proteins is characterized by the presence of hydrogen bonds between the carbonyl oxygen of the n th amino acid residue and the amide hydrogen of the: (n+4) th residue (n+3) th residue (n+2) th residue (n+1) th residue Which of the following tests gives a positive result (white/yellow precipitate turning brick red on heating) specifically for proteins containing the amino acid Tyrosine? Millon's test Biuret test Molisch test Xanthoproteic test Which of the following chemical tests is specifically used for the detection of the 'Guanidino' group present in the amino acid Arginine? Sakaguchi test Pauly's test Hopkins-Cole test Millon's test In enzyme kinetics, the Michaelis-Menten constant ( K m ) represents: The substrate concentration at which the reaction velocity is half of V max The maximum velocity of the enzyme-catalyzed reaction The equilibrium constant for the enzyme-substrate complex The rate constant of the formation of product Which of the following is a basic amino acid? Lysine Valine Serine Tyrosine In the tertiary structure of proteins, 'salt bridges' refer to which type of interaction? Ionic bonds between oppositely charged side chains Hydrogen bonds between peptide backbones Covalent disulfide linkages Hydrophobic interactions between non-polar residues Which of the following reagents is used in the Edman degradation method for determining the N-terminal amino acid sequence of a peptide? Phenyl isothiocyanate 2,4-Dinitrofluorobenzene Hydrazine Cyanogen bromide In protein chemistry, -mercaptoethanol is a common reagent used to: Reduce disulfide bonds into sulfhydryl groups Catalyze the formation of peptide bonds Denature the protein by breaking hydrogen bonds Stain proteins for visualization For a basic amino acid like Lysine ( pK a1 =2.18, pK a2 =8.95, pK aR =10.53 ), the isoelectric point ( pI ) is calculated as: (pK a2 + pK aR ) / 2 (pK a1 + pK a2 ) / 2 (pK a1 + pK aR ) / 2 (pK a1 + pK a2 + pK aR ) / 3 Which of the following amino acids is considered purely ketogenic (its breakdown yields only ketone bodies)? Leucine Alanine Glycine Valine Which of the following amino acids contains two chiral centers in its structure? Isoleucine Leucine Valine Alanine A certain protein contains 0.32 % sulfur by mass. If each molecule contains two atoms of sulfur, the approximate molecular mass of the protein is: 20,000 g/mol 10,000 g/mol 40,000 g/mol 5,000 g/mol The phenomenon where an α -helix is stabilized by hydrogen bonds occurs between the carbonyl group of the n th amino acid and the amino group of which amino acid? (n+4) th (n+1) th (n+3) th (n+2) th The peptide bond ( -CO-NH- ) is planar. This planarity is due to: Partial double bond character of the C-N bond due to resonance Hydrogen bonding between adjacent chains The sp 3 hybridization of Nitrogen Steric hindrance of the side chains Which of the following reagents is known as 'Sanger's Reagent' and is used for the determination of the N-terminal amino acid in a polypeptide chain? 1-fluoro-2,4-dinitrobenzene Phenylisothiocyanate Ninhydrin Benzyloxycarbonyl chloride