31 Years NEET Previous Year Questions: Biomolecules - 1 Free MCQ Practice

• Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.
• Enzymes are composed of two main parts: the protein portion and the non-protein portion.
• The protein portion of an enzyme is called an Apoenzyme, and it is inactive by itself.
• The non-protein part, which can either be a cofactor or coenzyme, binds to the apoenzyme to form an active enzyme known as a holoenzyme.

Holoenzyme = Apoenzyme + Coenzyme

Enzymes are divided into 6 classes, each with 4-13 subclasses and named accordingly by a four-digit number.

• Transferases: Enzymes catalysing a transfer of a group, G (other than hydrogen), between a pair of substrates S and S’

S - G + S' → S + S' - G

• Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
• Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction of two substrates S and S’.
• Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.
• Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.
• Ligases: Enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds

Catalase:

• Catalase is an enzyme that contains haem as its prosthetic group.
• It plays a critical role in protecting cells from oxidative damage by decomposing hydrogen peroxide (H₂O₂).
• The haem group in catalase contains iron, which is essential for the enzyme's catalytic activity.
• The reaction catalyzed by catalase is:
  2H₂O₂ → 2H₂O + O₂
• This enzyme is highly efficient and critical for maintaining cellular health in aerobic organisms.

Other Options:

RuBisCo:

• RuBisCo (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is a key enzyme involved in the Calvin cycle of photosynthesis.
• It catalyzes the fixation of carbon dioxide (CO₂) into organic compounds in plants.
• It does not contain haem; instead, it is a protein enzyme with no metalloprotein or haem group association.

Carbonic anhydrase:

• This enzyme catalyzes the reversible conversion of carbon dioxide (CO₂) and water (H₂O) into carbonic acid (H₂CO₃), which then dissociates into bicarbonate (HCO₃^-) and protons (H⁺).
• It contains zinc (Zn²⁺) as a cofactor

Succinate dehydrogenase:

• This enzyme is part of the citric acid cycle (Krebs cycle) and the electron transport chain in mitochondria.
• It facilitates the oxidation of succinate to fumarate and contains iron-sulfur clusters and FAD (flavin adenine dinucleotide) as cofactors.

Correct option: A

Adenosine is a nucleoside, formed by the linkage of the nitrogenous base adenine to the pentose sugar ribose. This corresponds to III.

Adenylic acid (AMP) is adenosine monophosphate, a nucleotide made of adenine, ribose and a phosphate group. This corresponds to II.

Adenine is a nitrogenous base found in nucleic acids. This corresponds to I.

Alanine is an α-amino acid used in protein synthesis. This corresponds to IV.

Therefore the correct matching is A-III, B-II, C-I, D-IV, i.e., option A.

To solve this matching question, we need to correctly identify what each item in List I represents and match it with its corresponding description in List II:

• GLUT-4 is a glucose transporter protein that allows glucose to be absorbed into cells when insulin is present. Hence, it should be matched with "Enables glucose transport into cells."
• Insulin is a hormone produced by the pancreas that helps regulate blood glucose levels by facilitating the uptake of glucose into tissues. It should be matched with "Hormone."
• Trypsin is an enzyme that aids in the digestion of proteins in the digestive system. It should be matched with "Enzyme."
• Collagen is a primary structural protein that forms connective tissues throughout the body, including the extracellular matrix. It should be matched with "Intercellular ground substance."

Here's how we match each term with the correct description from List II:

A-IV, B-I, C-II, D-III

This corresponds to:

• A (GLUT-4) - IV (Enables glucose transport into cells)
• B (Insulin) - I (Hormone)
• C (Trypsin) - II (Enzyme)
• D (Collagen) - III (Intercellular ground substance)

Therefore, the answer is Option A

The correct order of the steps in the catalytic cycle of enzyme action involves the following key events:

1. Substrate binding to the active site: Before any reaction can take place, the substrate must bind to the enzyme's active site. This is where the substrate is correctly positioned for the reaction.
2. Formation of the substrate-enzyme complex: Once the substrate binds to the active site, a substrate-enzyme complex is formed. This complex stabilizes the transition state of the reaction and lowers the activation energy required for the reaction.
3. Chemical bonds of the substrate broken : Within the substrate-enzyme complex, the specific chemical reaction occurs, leading to the breaking of bonds within the substrate. This step often involves changes to the chemical structure of the substrate, turning it into the product(s) of the reaction.
4. Release of products: After the reaction occurs, the product(s) of the reaction are released from the enzyme, leaving the enzyme unchanged.
5. Free enzyme ready to bind with another substrate: Once the product is released, the enzyme is free again to bind with another substrate, repeating the cycle.

Given the correct sequence and your provided options, the correct answer is: Option A
This sequence correctly describes the steps involved in the catalytic cycle of enzyme action, from substrate binding to the release of products and the readiness of the enzyme to start a new cycle.

(a) They are highly substrate specific: This is true. Enzymes are highly specific to the substrate they act upon, meaning they catalyze reactions with particular molecules.
(b) In thermophilic organisms, enzymes can catalyze reactions at high temperatures, i.e. 90°C: This is true. Thermophilic organisms have enzymes that can function at extremely high temperatures, even up to 90°C or more.
(c) All enzymes are proteinaceous in nature: This is incorrect. While most enzymes are proteins, some are made of RNA molecules, known as ribozymes.
(d) Some enzymes have metal ions: This is true. Many enzymes require metal ions (such as zinc, magnesium, or iron) to function properly as cofactors.
Therefore, the incorrect statement is (c).

• A. Glutamic acid: This is an amino acid, not a fatty acid.
• B. Arachidonic acid: This is a fatty acid. It is an essential polyunsaturated fatty acid found in the cell membranes.
• C. Palmitic acid: This is a fatty acid. It is a saturated fatty acid found in animal fats and plant oils.
• D. Lecithin: Lecithin is a phospholipid, not a fatty acid. It is composed of fatty acids, but it itself is not a fatty acid.
• E. Aspartic acid: This is an amino acid, not a fatty acid.

Therefore, A, D, and E are not fatty acids, making (c) A, D, and E only the correct answer.

• (a) Fatty acid: Fatty acids do not typically exist as zwitterions. They are usually in their ionized form at physiological pH.
• (b) Monosaccharide: Monosaccharides (simple sugars) do not form zwitterions. They generally have hydroxyl groups and do not carry both positive and negative charges on the same molecule.
• (c) Amino acid: This is correct. Amino acids, at physiological pH, exist as zwitterions. They contain both a positively charged amino group (—NH₃⁺) and a negatively charged carboxyl group (—COO^-), making them neutral overall but having both positive and negative charges.
• (d) Nucleic acid: Nucleic acids, such as DNA and RNA, do not exist as zwitterions. They contain acidic phosphate groups but are not zwitterions.

Therefore, the correct answer is (c) Amino acid.

The enzyme carboxypeptidase is well-known for its utilization of a zinc ion as a cofactor in its catalytic mechanism. The zinc ion plays a crucial role in the hydrolysis of peptide bonds, the reaction facilitated by carboxypeptidase. The presence of zinc allows for proper stabilization of water molecules which are necessary in the catalysis, making the hydrolysis of the peptide bond effective. This zinc dependency categorizes carboxypeptidase as a metalloenzyme.
Therefore, the correct answer is: Option A: Zinc
Other options mentioned, such as Niacin, Flavin, and Haem, serve as cofactors for different enzymes. For example, Niacin is involved in the formation of NAD+ (Nicotinamide adenine dinucleotide) which acts as an electron carrier in many enzymatic reactions. Flavins (like FMN and FAD) are involved in a myriad of oxidation-reduction (redox) reactions. Haem, found in hemoglobin and cytochromes, also plays crucial roles primarily in electron transfer processes and oxygen transport. These are not associated with the functioning of carboxypeptidase, which specifically requires zinc for its enzymatic activity.

Answer: Option C.

Lipase hydrolyses ester bonds in triglycerides, so it corresponds to II.

Nuclease cleaves the phosphodiester bonds in nucleic acids, so it corresponds to IV.

Protease hydrolyses peptide bonds in proteins, so it corresponds to I.

Amylase breaks glycosidic bonds in polysaccharides (starch), so it corresponds to III.

Thus the correct matching is A-II, B-IV, C-I, D-III, which is Option C.

• (a) Inulin: Inulin is a type of carbohydrate, specifically a fructan, that is a polysaccharide but is not considered a "complex" polysaccharide. It consists of fructose units and is typically used by plants as a storage carbohydrate.
• (b) Chitin: Chitin is a complex polysaccharide made of N-acetylglucosamine, found in the exoskeletons of arthropods and the cell walls of fungi. It is a complex polysaccharide.
• (c) Glucosamine: Glucosamine is not a polysaccharide itself but is an amino sugar that forms part of larger polysaccharides such as glycosaminoglycans (e.g., in cartilage).
• (d) N-acetyl galactosamine: This is an amino sugar that forms part of complex polysaccharides, such as glycosaminoglycans.

Therefore, Inulin is not a complex polysaccharide, making (a) the correct answer.

• A. Ribozyme (II. Non-proteinaceous enzyme): A ribozyme is a non-proteinaceous enzyme, meaning it is made of RNA and not protein.
• B. Lecithin (III. Lipid): Lecithin is a type of lipid, specifically a phospholipid, commonly found in cell membranes.
• C. Glut-4 (I. Glucose transport): GLUT-4 (Glucose transporter type 4) is involved in glucose transport in cells, particularly in muscle and fat cells.
• D. Vitamins (IV. Coenzyme): Vitamins often act as coenzymes or precursors to coenzymes in various metabolic reactions.

Therefore, the correct matching is A-II, B-III, C-I, D-IV.

• A. Collagen (III. Most abundant protein in animal world): Collagen is the most abundant protein in the animal world, providing structural support in tissues.
• B. GLUT-4 (IV. Enables glucose transport into cells): GLUT-4 is a glucose transporter that enables the transport of glucose into muscle and fat cells.
• C. Trypsin (I. Enzyme): Trypsin is a digestive enzyme that breaks down proteins in the small intestine.
• D. RuBisCO (II. Most abundant enzyme in biosphere): RuBisCO is the most abundant enzyme on Earth, playing a key role in the Calvin cycle of photosynthesis.

Therefore, the correct matching is A-III, B-IV, C-I, D-II.

• A. Toxin (III. Ricin): Ricin is a toxic protein derived from castor beans. It is a well-known toxin.
• B. Polymeric substance (I. Gum): Gums are polysaccharides or polymeric substances derived from plants that form gels when hydrated.
• C. Lectin (II. Concanavalin A): Concanavalin A is a type of lectin, which is a protein that binds to specific carbohydrate structures on cell surfaces.
• D. Drug (IV. Vinblastin): Vinblastine is a drug used in cancer treatment, particularly for its role in inhibiting cell division.

Therefore, the correct matching is A-III, B-I, C-II, D-IV.

The correct answer is option (b).
Some lipids have phosphorous and a phosphorylated organic compound in them. These are phospholipids. They are found in cell membrane. Lecithin is one example.
Option (c) is incorrect as glycerides are another group of lipids in which both glycerol and fatty acids are present.
Option (a) and (d) are incorrect as amino acids and carbohydrates are separate groups of biomolecules.

The inhibition of the enzyme succinic dehydrogenase by malonate is a classic example of competitive inhibition. To understand why this is the case, let's explore the mechanism and dynamics of this specific type of inhibition in the context of the given enzyme and inhibitor.
Competitive Inhibition: 
This type of enzyme inhibition occurs when an inhibitor compound resembles the substrate's structure and competes with the substrate for binding to the active site of the enzyme. If the inhibitor binds to the active site, it prevents the substrate from binding, temporarily blocking the enzyme’s activity. Importantly, competitive inhibition can typically be overcome by increasing the concentration of the substrate, as this can displace the inhibitor from the active site.
Succinic Dehydrogenase and Malonate: 
Succinic dehydrogenase is an enzyme that plays a critical role in the citric acid cycle, an essential metabolic pathway for energy production. It catalyzes the oxidation of succinate into fumarate. The structure of malonate is closely similar to that of succinate, the natural substrate of succinic dehydrogenase. Because of its structural similarity, malonate competes with succinate for the active site on succinic dehydrogenase. When malonate binds to the active site, it effectively inhibits the enzyme from catalyzing the reaction to convert succinate into fumarate.
Conclusion: 
Considering these points, Option C, Competitive inhibition, is correct for describing the inhibition of succinic dehydrogenase by malonate, as it directly competes with the substrate for the active site of the enzyme.
Other options such as cofactor inhibition, feedback inhibition, and enzyme activation do not accurately describe the situation with malonate and succinic dehydrogenase. Cofactor inhibition involves inhibition by substances that affect the enzyme's cofactors, feedback inhibition generally pertains to the regulation of biochemical pathways by their product, and enzyme activation is a process that increases the enzyme's activity, none of which apply in this context.

The graph that explains the effect of pH on enzyme activity typically shows that enzyme activity increases as the pH moves towards an optimal level, then decreases as the pH becomes too high or too low. This is a typical bell-shaped curve, where the enzyme activity is highest at a specific optimal pH, which matches the graph in option (a).

• C. The substrate binds with the active site of the enzyme: The substrate first binds to the enzyme's active site.
• B. Substrate induces the enzyme to alter its shape: The binding of the substrate often induces a conformational change in the enzyme (induced fit model).
• D. Enzyme-product complex is formed: The enzyme catalyzes the reaction, forming the enzyme-product complex.
• A. Enzyme releases products of the reaction and gets free: Finally, the enzyme releases the products and returns to its original form, ready for the next cycle.

Therefore, the correct order is C → B → D → A.

• Adenylic acid is a nucleotide, which consists of a nitrogenous base (adenine), a sugar (ribose or deoxyribose), and a phosphate group.
• Uridine is a nucleoside, not a nucleotide, as it lacks the phosphate group.
• Guanine is a nitrogenous base, not a nucleotide.
• Guanosine is a nucleoside, as it consists of the base guanine and a sugar but lacks the phosphate group.

• Lyases are enzymes that catalyze the removal of groups from substrates by mechanisms other than hydrolysis, often leaving double bonds. Examples include dehydratases, decarboxylases, and other enzymes that break bonds without the use of water.
• Transferases catalyze the transfer of functional groups.
• Oxidoreductases are enzymes that catalyze oxidation-reduction reactions.
• Dehydrogenases are a subclass of oxidoreductases that specifically catalyze the removal of hydrogen atoms.

• A. Primary structure of protein (III. Polypeptide chain): The primary structure of a protein refers to the sequence of amino acids in the polypeptide chain.
• B. Secondary structure of protein (IV. Alpha helix and β sheet): The secondary structure of a protein involves the regular folding of the polypeptide chain into structures like alpha helices and beta sheets.
• C. Tertiary structure of protein (II. Disulphide bonds): The tertiary structure refers to the overall three-dimensional shape of the protein, which is stabilized by interactions such as disulfide bonds.
• D. Quaternary structure of protein (I. Human haemoglobin): The quaternary structure is the arrangement of multiple polypeptide chains in a multi-subunit protein, like human hemoglobin.

Thus, the correct matching is A-III, B-IV, C-II, D-I.

The graph in (a) depicts the typical effect of substrate concentration on the velocity of an enzyme-catalyzed reaction. As the substrate concentration increases, the reaction velocity increases proportionally until it reaches a maximum velocity (Vmax), at which point all enzyme active sites are occupied, and further increases in substrate concentration do not increase the reaction rate. This is a classic Michaelis-Menten kinetics graph.

• Ligases are enzymes that catalyze the joining of two molecules, typically using energy derived from ATP or another nucleotide triphosphate. They are involved in forming various types of bonds, but not all bonds.
• (a) C-C: This is generally not catalyzed by ligases. C-C bond formation typically requires other mechanisms or enzymes.
• (b) P-O: Ligases can catalyze the formation of phosphodiester bonds (P-O), such as in the joining of DNA strands.
• (c) C-O: Ligases can catalyze the formation of C-O bonds, such as in the joining of alcohols and other molecules.
• (d) C-N: Ligases can also catalyze the formation of C-N bonds, for example, in the synthesis of peptides or other amide linkages.

Therefore, the bond that is not catalyzed by ligases is C-C.

Option (c) is the correct answer because cellulose does not contain complex helices and hence cannot hold iodine molecules. Option (a), (b) and (d) are not correct

Statement I is false - because the C-terminal represents the last amino acid in the protein chain, not the first. The N-terminal represents the first amino acid.
Statement II is true -  Adult human hemoglobin consists of 4 subunits: two subunits of α-type and two subunits of β-type. These subunits come together to form a complex protein structure responsible for carrying oxygen in the blood.
The correct option is (C): Statement I is false but Statement II is true

• Statement I is true - Low temperatures can slow down enzymatic reactions by placing the enzyme in an inactive state, and high temperatures can denature proteins, including enzymes, which can lead to a loss of enzymatic activity.
• Statement II is also true - A competitive inhibitor is a molecule that closely resembles the substrate of an enzyme and competes for the active site, thus reducing the enzyme's activity. This type of inhibition is called competitive inhibition.

So, the correct answer is : Option A : Both Statement I and Statement II are true.

Malonate is a competitive inhibitor of succinic dehydrogenase. Succinic dehydrogenase is an enzyme in the citric acid cycle (Krebs cycle) that helps in the conversion of succinate to fumarate. Malonate mimics succinate and competes for the same binding site on the enzyme, thereby inhibiting its activity and blocking the bacterial growth.

• Protein (A): Peptide bonds (IV) link amino acids in proteins.
• Unsaturated fatty acid (B): C=C double bonds (I) are present in unsaturated fatty acids, making them unsaturated.
• Nucleic acid (C): Phosphodiester bonds (II) join nucleotides in nucleic acids like DNA and RNA.
• Polysaccharide (D): Glycosidic bonds (III) link monosaccharides in polysaccharides like starch and cellulose.

Inulin is a carbohydrate polymer made up of fructose units linked together. It is a type of fructan and is commonly found in plants like chicory and Jerusalem artichoke. Inulin is used as a dietary fiber and has various health benefits.