Biomolecules - 1 - NEET Biology Class 11 Free MCQ Test with solutions

Enzymes have a particular optimum range of working temperature, below which their activity decreases.

Plant cell walls are made of cellulose. Paper made from plant pulp is cellulose.

Amino acids are organic compounds containing an amino group and an acidic group as substituents on the same carbon, i.e. the α-carbon. Hence, they are called α-amino acids.

Assertion (A): The formation of the enzyme-substrate complex is indeed a transient phenomenon and is crucial for catalysis, as it facilitates the reaction by bringing the substrate into proximity with the active site of the enzyme and lowering the activation energy. This is true.
Reason (R): The transition state structure is actually the least stable state, not the most stable state, during the conversion of substrate to product. The transition state is an intermediate, high-energy configuration that occurs before the substrate is converted into the product. This makes the Reason false.
Thus, the Assertion is true, but the Reason is false.

- Statement i is correct because polysaccharides can indeed be classified as homopolymers (like cellulose, which is made only of glucose) or heteropolymers (which contain different types of monosaccharides).

- Statement ii is incorrect; while cellulose is a homopolymer of glucose, it does not form complex helical structures. Instead, it has a linear structure that forms microfibrils.

- Statement iii is correct; starch serves as an energy reserve in plants and forms helical structures that can bind iodine, resulting in a blue complex.

- Statement iv is incorrect; glycogen is a highly branched polysaccharide, not linear, which allows for rapid mobilization of glucose when needed.

Thus, the correct statements are those in Option B: i and iii.

To analyze the statements:

- Statement i is correct; it describes the slow reaction rate in the absence of an enzyme.

- Statement ii is also correct; it accurately describes the function of carbonic anhydrase and its dramatic acceleration of the reaction rate.

- Statement iii is accurate; it notes that the pathway from glucose to pyruvic acid consists of ten enzyme-catalyzed reactions.

- Statement iv is incorrect; under anaerobic conditions, lactic acid is produced in skeletal muscle, not pyruvic acid.

Therefore, the correct answer, which includes statements i, ii and iii, is Option B.

• Statement i is correct because nucleic acids are indeed made up of polynucleotides that include ribose in RNA and deoxyribose in DNA.
• Statement ii is incorrect; the building blocks of nucleic acids are nucleotides, not amino acids (which are the building blocks of proteins).
• Statement iii is correct as it accurately lists the nitrogenous bases found in nucleic acids.
• Statement iv is incorrect; DNA contains deoxyribose, while RNA contains ribose.

Topic in NCERT: Nucleic acids

Line in NCERT: "for nucleic acids, the building block is a nucleotide. the sugar found in polynucleotides is either ribose (a monosaccharide pentose) or 2'-deoxyribose. a nucleic acid containing deoxyribose is called deoxyribonucleic acid (dna) while that which contains ribose is called ribonucleic acid (rna)."

- Statement i is correct because enzymes do require cofactors to be catalytically active, and the protein part without the cofactor is indeed called the apoenzyme.

- Statement ii is incorrect; prosthetic groups are tightly bound to the apoenzyme, not loosely associated.

- Statement iii is correct because coenzymes are indeed transiently associated with the apoenzyme and are often derived from vitamins, such as NAD from niacin.

- Statement iv is correct as certain enzymes do require metal ions, which are essential for their catalytic activity, forming coordination bonds at the active site.

Thus, the correct combination of statements is i, iii, and iv, corresponding to Option C.

Transferases are enzymes that facilitate the transfer of functional groups from one substrate to another, which is essential for various metabolic processes.

Topic in NCERT: Concentration of Substrate

Line in NCERT: "when the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. due to its close structural similarity with the substrate, the inhibitor competes with the substrate for the substrate-binding site of the enzyme."

To determine which statements are correct, let's analyze each one:

- Statement i: This statement describes the initial binding of the substrate to the enzyme's active site, which is accurate as enzymes typically have specific active sites that fit their substrates (the "lock and key" model).

- Statement ii: This statement is also correct. After the substrate binds, the enzyme undergoes an "induced fit," altering its shape for a tighter fit around the substrate.

- Statement iii: This statement correctly describes the formation of the enzyme-product complex, where the active site facilitates the breaking of chemical bonds in the substrate.

- Statement iv: This statement is incorrect. Enzymes are not permanently altered after the reaction; they can be reused to catalyze additional reactions.

Thus, the correct statements are i, ii, and iii, leading to the correct answer being Option D.

Correct option: C

Assertion is true. The acid-insoluble fraction of cellular material contains proteins, nucleic acids, polysaccharides and lipids.

Reason is false. The claim that lipids are classified as macromolecules because they exhibit polymeric characteristics is incorrect. Proteins, nucleic acids and polysaccharides are true polymers formed from repeating monomers (amino acids, nucleotides, monosaccharides respectively). In contrast, lipids are structurally diverse (for example, triglycerides, phospholipids, steroids) and do not consist of repeating monomeric chains; therefore they are not polymers.

Clarification: Lipids are important biomolecules and may be described as large molecules in a broad sense, but their lack of polymeric structure makes the Reason statement incorrect as an explanation for classifying them as macromolecules.

Because the Assertion is correct and the Reason is not a valid explanation, the correct choice is C.