Set-I: Past Entrance Papers

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(b) Primary metabolites are compounds that are directly involved in the growth and development of plant-like amino acids and sugars (glucose). Primary metabolites prominently function growth, development, and reproduction of cell. Secondary metabolites are compounds produced in other metabolic pathways that, although important, are not essential for the functioning of the plant.

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(c) Statements I, IV, and V are incorrect, while II and III are correct. The incorrect statements can be corrected as Lipid having only single bonds are called saturated fatty acids. Palmitic acid has 16 carbon atoms including carboxyl carbon. Arachidonic acid has 20 carbon atoms.

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(a) \((\mathrm{A})-(4),(\mathrm{B})-(1),(\mathrm{C})-(2),(\mathrm{D})-(3)\)
Proteins are polypeptides, they are linear chains of amino acids linked by a peptide bond.

Unsaturated fatty acids are carbon chains containing one or more double bonds with a terminal carboxylic acid. The two sugar molecules of nucleic acids are linked together via a phosphodiester bond.
Polysaccharides are long chains of sugar molecules joined with a covalent bond, i.e. glycosidic linkage.

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(a) Floridean starch has a structure similar to amylopectin and glycogen as both are made from \(\alpha\)-D glucose monomers. The key difference between
amylopectin and glycogen is, amylopectin is a soluble form of starch, while glycogen is an insoluble form of starch.

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(a) Collagen is the most abundant protein in the animal world and RuBisCO is the most abundant protein in the whole of the biosphere because it is present in every plant that undergoes photosynthesis and molecular synthesis through the Calvin cycle.

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(c) Inulin is a fructan(polysaccharide of fructose). Adjacent fructose units are linked through glycosidic bond. Insulin is a protein composed of 51 amino acids. Adjacent amino acids are attached through a peptide bond.

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(b) lysine is a basic amino acid because its side chain contains nitrogen and resembles
ammonia, which is a base. Valine is a neutral amino acid, glutamic acid is an acidic amino acid, while tyrosine is an aromatic amino acid.

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(a) is the correct match which is as follows Chemically, aquaporins are major intrinsic proteins that form pores in the membranes of cells. Asparagine is beta-amide derivative of aspartic acid. Abscisic acid is an apo-carotenoid. Chitin is a heteropolysaccharide consisting of two types of monosaccharide monomers.

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(d) It can be explained as follows. Malonate is the competitive inhibitor of catalytic activity of succinic dehydrogenase. Collagen is proteinaceous in nature and possesses peptide bonds. Chitin is a homopolymer present in the cell wall of fungi and exoskeleton of arthropods. Abrin and ricin are toxins, secondary metabolites.

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(b) ‘Ramachandran plot’ is used to confirm the structure of proteins.
Ramachandran plot is a plot of the angles-phi \((\varphi)\) and psi \((\psi)\) of amino acids found in a peptide chain. This plot was developed by GN Ramachandran, an Indian Scientist in 1963.

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(a) Chilled ethanol is used to precipitate DNA out of a mixture of biomolecules. Low temperature protects the DNA by slowing down the activity of enzymes that could break it apart and ethanol helps in the quick precipitation of DNA.

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(b) Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are tightly bound to the apoenzyme. For example, in peroxidase and catalase, which catalyse the breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is a part of the active site of the enzyme.

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(a) Statins are commercial blood cholesterol-lowering agent as they competitively inhibit the enzymes involved in cholesterol synthesis. They are obtained from a yeast, Monascus
purpureus. Streptokinase is a thrombolytic agent which is used to treat pulmonary
embolism and myocardial infarction. Lipases help to digest fat molecules while cyclosporin A is an immunosuppressant.

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(a) Statement A is true but B is false. Correct information about statement B is as follows. A complete catalytic, active enzyme with its bound prosthetic group is called holoenzyme. An apoenzyme is an inactive enzyme that gets activated by the binding of an organic or inorganic cofactor.

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(b) Purines, a heterocyclic compound, such as adenine and guanine are found both in DNA and RNA.

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(c) Lecithin (phosphatidylcholine) is a naturally occurring fatty substance referred to as phospholipid. It is important in cell structure and metabolism.

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(c) Concanavalin A is a secondary metabolite, e.g. lectin. Lectin is a mannose/ glucose-binding protein isolated from Jack beans (Canavalia ensiformis). They are not antibodies and do not originate in an immune system but bind specifically to carbohydrate containing receptors on cell surfaces (as of red blood cells).

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(d) GLUT1 and GLUT4 are glucose transport proteins that facilitate glucose transport into insulin-sensitive cells. GLUT1 is insulin independent and is widely distributed in different tissues. GLUT4 is insulin-dependent and is responsible for the majority of glucose transport into muscle and adipose cells in anabolic conditions.

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(d) Sugars are chemically carbohydrates. They are polyhydroxy aldoses, ketoses, and their condensation products. Aldoses bear a terminal aldehyde or – CHO group while ketoses have an internal ketone or – CO group. Thus, they possess two functional groups, i.e. carbonyl and hydroxyl.

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(c) Among the following, epinephrine is an amino acid-derived hormone. It is a catecholamine which is produced in the chromaffin cells of the adrenal medulla from amino acids tyrosine. On the other hand, estradiol and estriol are steroid hormones that are involved in the regulation of estrous and menstrual cycles. Ecdysone is also a steroid hormone that controls moulting in insects.

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(c) Ribozymes are RNA molecules having enzymatic activity, i.e. they are capable of catalysing specific biochemical reactions. Hence, they are nucleic acids with enzymatic function. TH Morgan is known as the ‘Father of Experimental Genetics.’ He worked on linkage, crossing over, linkage maps, etc.

In a dihybrid cross, two allelic pairs are used for crossing.

Mendel is considered as the ‘Father of Genetics. He proposed the laws of inheritance.

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(a) Holoenzyme is the complete conjugate enzyme consisting of an apoenzyme and a cofactor. Cofactor may be organic or inorganic in nature. Organic cofactors are of two types-coenzyme and prosthetic group.

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(c) Lipids are fatty acids esters of alcohols and related substances. Polysaccharides are polymers of monosaccharides. Proteins are polymers of amino acids and nucleic acids are polymers of nucleotides.

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(b) A ribozyme is a ribonucleic acid (RNA) enzyme that catalyses a chemical reaction in a similar way to that of a protein enzyme. These are found in ribosomes and are also called catalytic RNAs.

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(b) The graph shows the exothermic reaction A in the presence of enzyme as it lowers down the activation energy substantially.

The B graph shows this reaction in the absence of enzyme when activation energy is quite high. 

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(d) Tertiary structure or three-dimensional structure of a protein is stabilised by several types of bonds-hydrogen bonds, ionic bonds, van der Waal’s interactions, covalent bonds, and hydrophobic bonds.

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(d) Neutral or true fats are triglycerides that are formed by esterification of three molecules of fatty acids with one molecule of trihydric alcohol, glycerol (glycerine or trihydroxy propane).

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(b) Glycine is a neutral amino acid. Cysteine and methionine are sulphur-containing amino acids.

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(a) Chitin is a structural polysaccharide that constitutes the exoskeleton of arthropods. It is a complex carbohydrate in which \(\mathrm{N}\)-acetyl glucosamine monomers are joined together by \((1,4) \beta\)-linkages. Chitinous exoskeleton provides strength and elasticity to arthropods.

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(b) Phosphodiester bond is responsible for linking nucleotides in nucleic acid (DNA and RNA).

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(b) Competitive inhibition is a reversible inhibition where the inhibitor competes with the normal substrate for the active site of the enzyme. A competitive inhibitor is usually chemically similar to the normal substrate and therefore, fits into the active site of an enzyme and binds with it. The inhibition is thus due to substrate analogue. The enzyme, now cannot act upon the substrate, and reaction products are not formed. \(E. g\)., the activity of succinate dehydrogenase is inhibited by malonate. \(\mathrm{K}_{\mathrm{m}}\) value or Michaelis constant is defined as the substrate concentration at which half of the enzyme molecules are forming enzyme-substrate (ES) complex or concentration of the substrate when the velocity of the enzyme reaction is half the maximal possible. A smaller \(K_{m}\) value indicates greater affinity of the enzyme for its substrate, hence, showing a quicker reaction. The competitive inhibitor decreases the affinity of the enzyme for substrate, thus increasing the \(\mathrm{K}_{\mathrm{m}}\) value.

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(b) The reduction of activity of succinate dehydrogenase by malonate is an example of competitive inhibition. Competitive inhibition is a reversible inhibition where the inhibitor competes with the normal substrate for the active site of the enzyme. A competitive inhibitor is usually similar to the normal substrate and, therefore, fits into the active site of an enzyme and binds with it. The enzyme, now cannot act upon the substrate, and reaction products are not formed. Hence, the action of an enzyme may be reduced or inhibited. Since a competitive inhibitor occupies the site only temporarily, the enzyme action is not permanently affected. Thus, the addition of a lot of succinate can reverse the inhibition of succinic dehydrogenase by malonate.

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(b) In non-reducing sugars, a free aldehyde or ketonic group is absent. Sucrose is a non-reducing sugar formed by condensation of one molecule each of glucose and fructose with the release of a water molecule. A glycosidic bond is established between carbon atom 1 of glucose and carbon atom 2 of fructose.

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(a) Phosphoglycerides are the triesters of fatty acids (either saturated or unsaturated) and glycerol to which a phosphate group is also attached.

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(c) Macromolecule chitin is a complex polysaccharide containing amino sugars and chemically modified sugars, (e.g. glucosamine, \(\mathrm{N}\)-acetyl galactosamine, etc). Polysaccharides are long carbohydrate molecules of monosaccharide units joined together by glycosidic bonds. They have a general formula \(\mathrm{C}_{x}\left(\mathrm{H}_{2} \mathrm{O}\right)_{y}\). Chitin is the main component of the cell wall of fungi, the exoskeletons of arthropods, insects and radulae of molluscs, etc.

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(a) Transition state is the formation of the unstable intermediate structural state. During this, substrate bonds are broken and new bonds are established that transform the substrate molecules into products. This state is transient and highly unstable.

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(b) Coenzyme is the non-protein organic group that gets attached to the apoenzyme to form holoenzyme or conjugate enzyme. It helps in removing a product of a chemical reaction besides bringing contact between the substrate and the enzyme. Most of the coenzymes are made of water-soluble vitamins B and C, e.g., thiamine, riboflavin, nicotinamide, and pyridoxine.

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(b) Enzymes are mostly proteins but some are RNA (ribozymes). No lipid working as enzymes are known.

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(a) A nucleoside is pentose sugar and base together, without the phosphate group. Uracil is present as uridine in RNA only.
\(\text { Uracil }+\text { Ribose } \rightarrow \text { Uridine }\)

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(a)
A – Serine (Neutral – Polar)
B – Cysteine(Neutral – Polar)
C – Tyrosine(Neutral – Polar)
D – Not an amino acid

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(b) Basic amino acids have an additional amino group without forming amides thus they are diamino monocarboxylic acids e. g., arginine, lysine, etc.

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(c) Collagen is an insoluble fibrous protein found extensively in the connective tissue of skin, tendons, and bone. Collagen accounts for over 30% of the total body proteins of mammals and it is the most abundant animal protein.

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(d) The given structure corresponds with the structure of ribose sugar. As it lacks a phosphoric acid hence it can be a nucleoside, not a nucleotide.

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(c) Phosphorus is present in the plasma membrane in the form of phospholipid bilayer. It is an essential component of all nucleic acids, not ‘certain’ nucleic acids. Moreover, phosphorus is never found in proteins.

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(a) Lecithin is a triglyceride lipid where one fatty acid is replaced by phosphoric acid which is linked to additional nitrogenous group called choline. It is a common membrane lipid. It is an amphipathic phospholipid having both hydrophilic polar and hydrophobic nonpolar groups. The hydrocarbon chains of two fatty acids function as hydrophobic nonpolar tails whereas the phosphate and choline behave as hydrophilic polar head group of the molecule.
Palmitic acid is a saturated fatty acid (as it does not possess double bonds in its carbon chain) and contains 16 carbon atoms with formula \(\mathrm{C}_{16} \mathrm{H}_{32} \mathrm{O}_{2}\).

Adenylic acid or adenosine monophosphate is a nucleotide formed by the union of adenine (nitrogenous base), ribose (pentose sugar), and phosphate. It is formed through phosphorylation of nucleoside as phosphate combines with sugar molecule at its \(5^{\prime}\) carbon atom. Amino acids are organic acids with carboxylic group (-COOH) having amino group (\(\mathrm{NH}_{2}\) ) generally attached to \(\alpha\)-carbon or carbon next to the carboxylic group. Alanine is a nonpolar and neutral amino acid having one methyl group and having amino group attached to carbon next to the carboxylic group.

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(b) Enzymes generally function in a narrow range of temperature and \(\mathrm{pH}[latex]. Each enzyme shows its highest activity at a particular temperature and [latex]\mathrm{pH}\) called the optimum temperature and optimum \(\mathrm{pH}\). Activity declines both below and above the optimum values. X-axis always represents temperature or \(\mathrm{pH}\) and \(Y\) axis represents enzyme activity.

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(d) ‘A’ is a structural formula of lecithin. It is probably the most common phospholipid. Phospholipids are major components in the lipid bilayers of the cell membrane.

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(d) Most enzymes are proteins but some are RNA enzymes e.g., ribozymes. Ribozymes are RNA molecules that exhibit enzyme (catalytic) activities. Ribozymes provide resistance to several viruses which is being applied in biotechnology in producing cDNA that encodes for ribozyme and integrates it into the host plant genome for developing resistant plants.

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(b) According to the most widely accepted mechanism of enzyme action, the enzyme molecule binds the substrate molecule to form a temporary transition state (label A) which rapidly degrades into enzyme molecule and product. The transition state has higher free energy than the substrate (label B) or product molecule. Thus a substrate has to pass through the energy barrier in order to form the product molecule. An uncatalyzed reaction (label C) has to cross a higher barrier as compared to a reaction catalysed by an enzyme (label D). Thus, enzymes work by reducing the free energy barrier between substrates and the product molecules.

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(b) The wrongly matched pair is ‘ \(b\) ‘ because alcohol (ethyl alcohol)can be produced by fermentation of any carbohydrate, containing a fermentable sugar.

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(d) There are total five nitrogenous bases found in nucleic acids. Out of this adenine, guanine (purines), and cytosine, thymine (pyrimidines) are present in DNA, while RNA contains uracil in place of thymine (both pyrimidines)along with rest 3 similar to DNA.

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(d) Starch is the major storage carbohydrate of plants. In most plant species it is accumulated in the chloroplast of leaves, whereas in storage organs it accumulates in the amyloplast as reserve starch. It is the osmotically inactive form of photosynthetic product and is a hexosan polysaccharide made of large number of glucose unit so, chemically non-reactive.

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(c) The cell wall of most fungi consists of chitin or cellulose. In Pythium, the hyphal wall contains cellulose whereas, in yeast, the cell wall is thin and is composed of chitin in combination with other compounds (carbohydrates, glucan, and mannan). The bacterial cell wall contains \(\mathrm{N}\)-acetyl glucosamine and N-acetyl muramic acid.

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(c) Competitive inhibition is a form of enzyme inhibition where binding of the inhibitor to the active site on the enzyme prevents binding of the substrate and vice versa. Malonate is a competitive inhibitor of the enzyme succinate dehydrogenase: malonate binds to the active site of the enzyme without reacting, and so competes with succinate, the usual substrate of the enzyme.

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(d) Modern detergents contain enzyme preparation of alkaline protease which are called alkaliphiles, for removing protein stains.

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(d) Living organisms requires 6 elements in relatively large amounts. \(\mathrm{C}, \mathrm{H}, \mathrm{O}, \mathrm{N}, \mathrm{P}, \mathrm{S}\). These elements contribute to the structural organization of living organisms.

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(d) In DNA molecule the adjacent deoxyribonucleotides are joined in a chain by phosphodiester bridges or bonds, which link the \(5^{\prime}\) carbon of deoxyribose of one mononucleotide unit with3’carbon of deoxyribose of next mononucleotide unit.

According to Watson and Crick DNA molecule consists of two such polynucleotide chains wrapped helically around each other, with the sugar-phosphate chain on the outside and purine and pyrimidine on the inside of helix.

The two strands run antiparallel, i.e. one strand has phosphodiester linkage in \(3^{\prime}\) \(\rightarrow 5^{\prime}\) direction while other strand has phosphodiester linkage in \(5^{\prime} \rightarrow 3^{\prime}\) direction.
Chargaff \((1950)\) suggested that despite wide compositional variations exhibited by different types of DNA the total amount of purines equaled the total amount of pyrimidines \((A+G=T+C)\).

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(c) In 1953 James Watson and Francis Crick suggested that in a DNA molecule there are two polynucleotide chains arranged antiparallel or in opposite directions.

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(c) The lipids of the cell membrane are of three types namely phospholipids, glycolipids, and sterols. The sterol found in the membrane may be cholesterol (animals), phytosterol(plants), or ergosterol (microorganisms). The cell membrane is made up of lipid+protein \((60 \%)\) and carbohydrates (2-10%). Proline is an amino acid.

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(b) Enzymes are simple if they are made of only proteins (e.g., pepsin, amylase, etc.) while conjugate enzymes have an additional non-protein cofactor which may be organic or inorganic. The loosely attached organic cofactor is the coenzyme. It plays an accessory role in enzyme-catalyzed processes often by acting as a donor or acceptor of a substance involved in the reaction. ATP and NAD are common coenzymes.