NEET Practice Questions (MCQs) with Answers & Solutions

(b) Ribozyme is a form of ribosomal RNA (23 SrRNA) which acts as a catalyst in splicing of RNA during protein synthesis. It is the only non-protein enzyme known so far, rest all the enzymes are proteinaceous. Hence, option (b) is correct.

(d) Carbohydrates, fats and proteins all can be used as a substrate in cellular respiration. All of them first get converted to acetyl Co-A to enter into Kreb's cycle of aerobic cellular respiration. Thus, it is the common factor of respiration entering Kreb's cycle after breakdown of carbohydrates, fats and proteins

(d) Ester bonds are the least likely to be involved in stabilising the 3D-folding of most proteins. A long protein chain gets folded upon itself like a hollow woolen ball, giving rise to a tertiary structure (3D) structure. This structure is stabilised by several type of bonds, i.e. hydrogen bonds, ionic bonds, Vander waal's interactions, covalent bonds and hydrophobic bonds. Ester bond is formed between sugar and phosphate in a nucleotide and is not involved in stability of a polypeptide chain. Thus, option (d) is correct.

(c) Glycine is the simplest amino acid in which functional group 'R' is replaced by hydrogen atom (H).

(a) A typical fat molecule is triglyceride formed by esterification of one glycerol and three fatty acid molecules. The three fatty acids can be of same type or different depending on type of the fat molecules.

(d) In the presence of a competitive inhibitor, V_max remains unchanged while K_m increases.

(c) A fat is formed of two kinds of smaller molecules, i.e, glycerol, and fatty acids. In making a fat, three fatty acid molecules each join o glycerol by an ester linkage. A fatty acid has a long carbon skeleton, usually 16 or 18 carbon atoms in length. If there are no double bonds between carbon atoms composing the chain, then as many hydrogen atoms as possible are bonded to the carbon skeleton. This is called saturated fatty acid. Unsaturated fatty acid has one or more double bonds. Phosphoglycerides are esters of two fatty acids, phosphoric acid, and a trifunctional alcohol glycerol. The fatty acids are attached to the glycerol at the 1 and 2 positions on glycerol through ester bonds.

(c) Collagen is the most abundant protein (structural protein) in the animal world while Ribulose Carboxylase Oxygenase (RUBISCO) is the most abundant protein in the whole of a plant world.

The pair 'Alcohol - Nitrogenase' is wrongly matched. Nitrogenase is an enzyme involved in nitrogen fixation, not alcohol metabolism. Alcohol is metabolized by enzymes like alcohol dehydrogenase and aldehyde dehydrogenase.

(a) Succinic dehydrogenase oxidised the succinate to fumarate. in eukaryotes succinate dehydrogenase is tightly bound to the inner mitochondrial membrane, in prokaryotes to the plasma membrane. Electrons pass from succinate through the FAD and iron-sulphur centres before entering the chain of electron carriers in the mitochondrial inner membrane. Malonate, an analogue of succinate is a strong competitive inhibitor of succinate dehydrogenase and therfore, blocks the activity of citric acid cycle.

In Krebs cycle the reversible hydration of fumarate to malate is catalysed by fumarase enzyme.

In the last reaction of Krebs cycle NAD-linked L-malate dehydrogenase catalyses the oxidation of L-malate to oxaloacetate.

The isocitrate dehydrogenase in Krebs cycle catalyses oxidative decarboxylation of isocitrate to form $\mathrm{\alpha }$-ketoglutarate, which in next step through oxidative decarboxylation converted to succinyl Co-A.