Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
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Assertion: Amino acids are called \(\alpha\)-amino acids.
Reason: Amino acids are organic compounds containing an amino group and an acidic group as substituents on the \(\alpha\)-carbon.
a
Assertion: Palmitic acid has 20 carbon atoms including carboxyl carbon.
Reason: Saturated fatty acids do not possess double bonds in their carbon chains.
(d) A fatty acid has a carboxyl group attached to an R group. The \(\mathrm{R}\) group could be a methyl \(\left(-\mathrm{CH}_3\right)\), or ethyl \(\left(-\mathrm{C}_2 \mathrm{H}_5\right)\) or higher number of \(-\mathrm{CH}_2\) groups (1 carbon to 19 carbons). Palmitic acid has 16 carbons atoms including carboxyl carbon. Arachidonic acid has 20 carbon atoms including the carboxyl carbon.
Assertion: A protein is a heteropolymer.
Reason: Dietary proteins are the source of nonessential amino acids.
(c) Each protein is a polymer of amino acids. As there are 20 types of amino acid, a protein is a heteropolymer and not a homopolymer. Amino acids can be essential or non-essential. Certain amino acids are essential for our health and they have to be supplied through our diet. Hence, dietary proteins are the source of essential amino acids. Non-essential amino acids are those amino acids which are synthesised in our body.
Assertion: The exoskeleton of arthropods is made up of complex polysaccharide called chitin.
Reason: Plant cell walls are made up of cellulose.
(b) Polysaccharides are complex carbohydrates which are formed by polymerisation of large number of monosaccharide monomers. Exoskeletons of arthropods contain a complex polysaccharide called chitin. These complex polysaccharides are heteropolymers. Plant cell walls are made up of cellulose. Paper made from plant pulp and cotton fibre is cellulosic. Cellulose is homopolysaccharide.
Assertion: The heterocyclic compounds in nucleic acid are the nitrogenous bases.
Reason: Adenine and guanine are substituted pyrimidines while uracil, cytosine and thymine are substituted purines.
(c) Nucleic acids are polynucleotides. A nucleotide has three chemically distinct components. One is a heterocyclic compound, the second is a monosaccharide and the third a phosphoric acid or phosphate. The heterocyclic compounds in nucleic acids are the nitrogenous bases named adenine, guanine, uracil, cytosine and thymine. Adenine and guanine are substituted purines while the rest are substituted pyrimidines formed from the skeletal heterocyclic rings purine and pyrimidine, respectively.
Assertion: The long protein chain is folded upon itself like a hollow ball giving rise to the tertiary structure.
Reason: Tertiary structure gives a 3-dimensional view of a protein.
(b) The primary structure of protein is the sequence of amino acids in a chain, i.e., the positional information in a protein. In the secondary structure protein thread is folded in the form of a helix or in the sheet form. The long protein chain is also folded upon itself like a hollow woolen ball, giving rise to the tertiary structure. This gives us a 3-dimensional view of a protein. Tertiary structure is absolutely necessary for many biological activities of proteins.
Assertion: The living state is an equilibrium steady state to be able to perform work.
Reason: Living process is a constant effort to prevent falling into equilibrium.
(d) The living systems maintain the concentration of biomolecules because they are in metabolic flux, always remaining in non-equilibrium steady state where equilibrium is seldom achieved. No work can be carried out in equilibrium state. Therefore, living systems are regularly receiving an input of energy to prevent reaching an equilibrium and remain always in non-equilibrium steady state. Energy is obtained from metabolism. Metabolism and living state are therefore, complementary and synonymous.
Assertion: All enzymes are not proteins.
Reason: RNA molecules that possess catalytic activity are called ribozymes.
(a) Almost all enzymes are proteins. They may have additional inorganic or organic substances for their activity. There are some RNA molecules that behave like enzymes. These are called ribozymes.
Assertion: Inorganic catalysts work efficiently at high temperature.
Reason: Enzymes get damaged at high temperature.
b
Assertion: Most of the chemical reactions do not start automatically.
Reason: Reactant molecules have an energy barrier to become reactive.
(a) The chemical or metabolic conversion refers to a reaction. Most of the chemical reactions do not start automatically because the reactant molecules have an energy barrier to become reactive. Therefore, an external supply of energy is needed for the start of the chemical reaction. It is called activation energy. Enzymes lower the activation energy required for a reaction.
Assertion: Each enzyme has a substrate binding site in its molecule which forms highly reactive enzymesubstrate complex.
Reason: The enzyme-substrate complex is long-lived and dissociates into its product and unchanged enzyme.
(c) A particular substrate molecule is acted upon by a particular enzyme. After coming in contact with the active site (a pocket into which the substrate fits) of the enzyme, the substrate molecules or reactants form a complex called enzyme-substrate complex. The enzyme substrate complex is short lived. In the complex state, the molecules of the substrate undergo chemical change. The products remain attached to the enzyme for some time so that an enzyme-product complex is also formed. However, the products are soon released and the freed enzyme is able to bind more substrate molecules.
Assertion: The inhibition of activity of succinic dehydrogenase by malonate which closely resembles the substrate succinate in structure is the example of competitive inhibition.
Reason: Competitive inhibition is the inhibition of enzyme activity when inhibitor closely resembles the substrate, in its molecular structure.
a
Assertion: Hydrolases are the enzymes which catalyse the hydrolysis of ester, ether, peptide, glycosidic, \(C-C\) or \(\mathrm{P}-\mathrm{N}\), etc. bonds.
Reason: Lyases are the enzymes catalysing the linking together of 2 compounds like joining of \(C-0, C-N\), \(P-0\), etc. bonds.
(c) There are various types of enzyme depending on their action. Hydrolases catalyse the hydrolysis of ester, ether, peptide, glycosidic, \(\mathrm{C}-\mathrm{C}, \mathrm{C}-\) halide, \(\mathrm{P}-\mathrm{N}\) bonds, etc., which are formed by dehydration and condensation. Hydrolases break up large molecules into smaller ones with the help of hydrogen and hydroxyl groups of water molecules. The phenomenon is called hydrolysis. Lyases are the enzymes which cause cleavage, removal of groups without hydrolysis, addition of groups to double bonds or removal of a group producing double bond, e.g., histidine decarboxylase breaks histidine to histamine and \(\mathrm{CO}_2\).
Assertion: The protein part of the enzyme is called apoenzyme and non-protein part of the enzyme is called co-factor.
Reason: Zinc is a co-factor for the proteolytic enzyme carboxypeptidase.
b
Assertion: Coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain a vitamin.
Reason: The association of co-enzyme with apoenzyme is enduring.
(c) Co-enzymes are also organic compounds but their association with the apoenzyme is only transient, usually occurring during the course of catalysis. Co-enzymes serve as co-factors in a number of different enzyme catalysed reactions. The essential chemical components of many coenzymes are vitamins, e.g., coenzyme nicotinamide adenine dinucleotide (NAD) and NADP contain the vitamin niacin.
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