Enzymes Questions in English

(B) In certain biological systems,$RNA$ molecules can exhibit catalytic activity,similar to protein-based enzymes. These catalytic $RNA$ molecules are known as $Ribozymes$. For example,the $23S$ $rRNA$ in the large subunit of the ribosome acts as a ribozyme during peptide bond formation. Therefore,the correct option is $B$.

(A) The reaction shown is the hydrolysis of the disaccharide lactose into its constituent monosaccharides,glucose and galactose.
This reaction is specifically catalyzed by the enzyme lactase (also known as $\beta$-galactosidase).
Protease breaks down proteins,maltase breaks down maltose,and amylase breaks down starch.
Therefore,the correct enzyme is lactase.

(C) The catalytic cycle of an enzyme action can be described in the following steps:
$1$. First, the substrate binds to the active site of the enzyme, fitting into the active site, which forms an Enzyme-Substrate $(ES)$ complex.
$2$. This complex is a transient state. During this state, the enzyme alters the shape of the substrate to form the Enzyme-Product $(EP)$ complex.
$3$. Finally, the enzyme releases the product$(s)$ and the enzyme is free to bind to another substrate molecule.
Therefore, the missing intermediate in the reaction sequence $\text{Enzyme} + \text{Substrate} \rightarrow ? \rightarrow \text{Enzyme} + \text{Product}$ is the Enzyme-Substrate complex.

(C) The correct answer is $C$.
Enzymes are biological catalysts that speed up chemical reactions.
While many enzymes are reversible,not all enzymes have a bidirectional effect.
Some enzymes catalyze reactions that are essentially irreversible under physiological conditions due to large negative changes in Gibbs free energy (e.g.,hexokinase in glycolysis).
Therefore,the statement that 'all enzymes have a bidirectional effect' is incorrect.
Other statements are correct: enzymes are sensitive to $pH$,they are amphoteric (due to amino acid side chains),and they exhibit high substrate specificity.

(C) Hydrolases are enzymes that catalyze the hydrolysis of various bonds (such as $C-O$,$C-N$,$C-C$,etc.) by adding water $(H_2O)$ to the substrate. This process breaks down complex organic molecules into simpler ones. Therefore,enzymes that catalyze the breakdown of complex substances by adding water are classified as Hydrolases.

(A) Enzymes are classified into six classes based on the type of reaction they catalyze.
Ligases are enzymes that catalyze the linking together of two compounds.
For example,enzymes that catalyze the joining of $C-O$,$C-S$,$C-N$,or $C-C$ bonds are called ligases.
Acetyl-CoA synthetase is a well-known example of a ligase,as it catalyzes the formation of a bond between acetate and Coenzyme-$A$ using $ATP$ energy.

(C) Chemically,almost all enzymes are proteins. They are complex macromolecules formed by the folding of polypeptide chains. While some $RNA$ molecules (ribozymes) can act as enzymes,the vast majority of biological catalysts are proteinaceous in nature.

(B) Enzymes are classified into six main classes based on the type of reaction they catalyze.
Aldolase is an enzyme that catalyzes the cleavage of $C-C$ bonds in a substrate without the use of water or oxidation-reduction.
This specific type of reaction,where bonds are broken by means other than hydrolysis or oxidation,is characteristic of the class $Lyases$.
Therefore,aldolase belongs to the class $Lyases$.

(C) Enzymes are classified into $6$ main classes based on the type of reaction they catalyze.
$1$. Oxidoreductases/Dehydrogenases: These enzymes catalyze oxidoreduction between two substrates $S$ and $S'$ by transferring electrons or hydrogen atoms.
$2$. Transferases: These catalyze the transfer of a group between two substrates.
$3$. Hydrolases: These catalyze the hydrolysis of ester,ether,peptide,or glycosidic bonds.
$4$. Lyases: These catalyze the removal of groups from substrates by mechanisms other than hydrolysis.
$5$. Isomerases: These catalyze the interconversion of optical,geometric,or positional isomers.
$6$. Ligases: These catalyze the linking together of two compounds.
Therefore,enzymes involved in oxidation and reduction reactions are known as Oxidoreductases.

(A) The specific region on the surface of an enzyme molecule to which the substrate binds is known as the $Active$ $site$.
This site is formed by the specific arrangement of amino acid residues that create a pocket or cleft,allowing the substrate to fit precisely,often described by the $Lock$ $and$ $Key$ model or $Induced$ $Fit$ model.
Therefore,the correct option is $A$.

(D) Lipase is an enzyme that catalyzes the hydrolysis of fats (lipids).
It breaks down lipids into fatty acids and glycerol.
Therefore,the correct option is $D$.

(D) An apoenzyme is the protein part of a conjugated enzyme.
It is the inactive form of an enzyme that requires a cofactor (such as a coenzyme or metal ion) to become catalytically active.
Since enzymes are primarily composed of amino acid chains,the apoenzyme component is essentially a protein.

(B) Hexokinase is an enzyme that catalyzes the phosphorylation of glucose to glucose$-6-$phosphate by transferring a phosphate group from $ATP$ to glucose.
Since this enzyme facilitates the transfer of a functional group (a phosphate group) from one molecule to another,it is classified as a $Transferase$.

(A) Biological catalysts are substances that increase the rate of biochemical reactions without being consumed in the process. Enzymes are proteinaceous molecules that act as biological catalysts in living organisms. They lower the activation energy required for a reaction to proceed,thereby accelerating metabolic processes.

(B) Enzymes are biological catalysts that speed up chemical reactions in living organisms.
They are primarily composed of proteins,which give them a complex three-dimensional structure.
Because of their proteinaceous nature,they are generally water-soluble and exist in a colloidal state in the cellular environment.
Therefore,the correct answer is $B$ (Enzymes).

(B) Enzymes are biological catalysts that are produced by living cells. They are typically proteins (with some exceptions like ribozymes) that speed up biochemical reactions by lowering the activation energy required for the reaction to occur. They are effective in very small amounts and remain unchanged at the end of the reaction.

(C) Enzymes are biological catalysts that increase the rate of biochemical reactions without being consumed in the process.
$1$. Most enzymes are proteins (except ribozymes).
$2$. They act as biological catalysts.
$3$. They are secreted by living cells in small quantities.
$4$. $A$ key characteristic of catalysts is that they remain chemically unchanged at the end of the reaction,meaning they are recovered in their original form.
Therefore,the statement that they are not recovered in their original form is incorrect.

(C) Some nucleic acids,specifically certain $RNA$ molecules,possess catalytic activity and can accelerate biochemical reactions. These catalytic $RNA$ molecules are known as $Ribozymes$. Unlike most enzymes which are proteins,these are nucleic acids that function as enzymes.

(B) An enzyme is a biological catalyst that speeds up chemical reactions in living organisms.
The specific molecule upon which an enzyme acts is known as the $Substrate$.
When the enzyme binds to the $Substrate$,it forms an $Enzyme-Substrate$ complex,which eventually converts the $Substrate$ into the $Product$.

(D) In a biochemical reaction,the substances that undergo chemical changes are called reactants or substrates. The substances that are formed as a result of the reaction are known as products. Therefore,the component produced at the end of a biochemical reaction is called a product.

(D) Lactose is a disaccharide composed of glucose and galactose units linked by a $\beta-1,4-glycosidic$ bond.
The enzyme responsible for breaking this bond through hydrolysis is $Lactase$.
$Lactose + H_2O \xrightarrow{Lactase} Glucose + Galactose$.
Therefore,the correct option is $D$.

(D) Many enzymes are composed of a protein part and a non-protein part.
The protein portion of an enzyme is known as the $Apoenzyme$.
The non-protein part is collectively known as the $Cofactor$.
When the $Apoenzyme$ combines with the $Cofactor$,the resulting active enzyme is called the $Holoenzyme$.

(B) The active site of an enzyme is a specific region or pocket where the substrate molecules bind to undergo a chemical reaction.
This binding forms an enzyme-substrate complex,which facilitates the conversion of the substrate into the product.
Therefore,the correct answer is the substrate.

(A) The catalytic cycle of an enzyme action involves the following steps:
$1$. First,the substrate binds to the active site of the enzyme,fitting into the active site.
$2$. The binding of the substrate to the enzyme induces the enzyme to alter its shape,fitting more tightly around the substrate.
$3$. This temporary association between the enzyme and the substrate is known as the $Enzyme-Substrate$ $(ES)$ complex.
$4$. The enzyme then breaks the chemical bonds of the substrate and a new $Enzyme-Product$ $(EP)$ complex is formed.
$5$. Finally,the enzyme releases the products of the reaction and the free enzyme is ready to bind to another molecule of the substrate.

(B) The minimum amount of energy that must be provided to compounds to result in a chemical reaction is called activation energy. In biological systems,enzymes lower this activation energy,thereby increasing the rate of the reaction.

(A) According to the mechanism of enzyme action,the enzyme binds with the substrate to form an $Enzyme-Substrate$ $(ES)$ complex.
This complex is transient and eventually converts into an $Enzyme-Product$ $(EP)$ complex.
Finally,the product is released from the active site of the enzyme,and the enzyme remains unchanged to bind with another substrate molecule.
Therefore,the substance released at the end of the reaction is the product.

(D) The equation represents the mechanism of enzyme action.
$E$ stands for the enzyme, $S$ stands for the substrate, and $E-S$ represents the enzyme-substrate complex.
According to the model of enzyme catalysis, the enzyme binds to the substrate to form an enzyme-substrate complex, which then dissociates to release the enzyme and the product $(P)$.
Therefore, the equation $E + S \rightarrow E-S \text{ Complex} \rightarrow E + P$ shows that "$a$" represents the product $(P)$.

(C) According to the International Union of Biochemistry and Molecular Biology $(IUBMB)$ nomenclature system,the names of enzymes are generally derived from the substrate they act upon or the reaction they catalyze.
To standardize this,the suffix $ -ase $ is added to the name of the substrate or the type of reaction to form the enzyme's name.
For example,the enzyme that acts on sucrose is called sucrase,and the enzyme that catalyzes the breakdown of proteins is called protease.
Therefore,the correct suffix is $ -ase $.

(D) Enzymes that catalyze oxidation-reduction reactions are classified as Oxidoreductases. These enzymes catalyze the transfer of electrons from one molecule (the reductant) to another (the oxidant). While 'Oxidase' is a specific type of enzyme that catalyzes oxidation,the broader class that encompasses all enzymes involved in oxidation-reduction reactions is 'Oxidoreductase'.

(C) Enzymes are classified into six main classes based on the type of reaction they catalyze.
$1$. Dehydrogenases are enzymes that catalyze the removal of hydrogen atoms from a substrate,effectively acting as oxidoreductases.
$2$. Hydrolases catalyze the hydrolysis of ester,ether,peptide,or $C$-$C$ bonds.
$3$. Reductases catalyze reduction reactions.
$4$. Oxidases catalyze oxidation reactions by transferring electrons to oxygen.
Therefore,the enzyme responsible for the removal of hydrogen is Dehydrogenase.

(A) Enzymes are classified into six classes based on the type of reaction they catalyze.
$1$. Oxidoreductases/Dehydrogenases: These enzymes catalyze oxidoreduction between two substrates.
$2$. Transferases: These catalyze the transfer of a group between a pair of substrates.
$3$. Hydrolases: These catalyze the hydrolysis of ester,ether,peptide,or glycosidic bonds.
$4$. Lyases: These catalyze the removal of groups from substrates by mechanisms other than hydrolysis.
$5$. Isomerases: These catalyze the interconversion of optical,geometric,or positional isomers.
$6$. Ligases: These catalyze the linking together of two compounds.
Within the class of Oxidoreductases,enzymes that catalyze the incorporation of molecular oxygen $(O_2)$ into substrates are specifically called Dioxygenases. Therefore,the correct option is $A$.

(C) Transferases are enzymes that catalyze the transfer of a functional group (e.g.,methyl,amino,phosphate,etc.) from one substrate to another.
According to the $IUBMB$ classification,transferases catalyze the transfer of a group $G$ (other than hydrogen) between a pair of substrates $S$ and $S'$.
The reaction is represented as: $S-G + S' \rightarrow S + S'-G$.
Since the definition explicitly states that transferases catalyze the transfer of groups other than hydrogen,hydrogen is the group that is $NOT$ transferred by this class of enzymes.
Dehydrogenation (transfer of hydrogen) is catalyzed by oxidoreductases,not transferases.

(A) Enzymes classified as $Transferases$ catalyze the transfer of a group,other than hydrogen,between a pair of substrates.
Specifically,enzymes like $Hexokinase$ (a type of transferase) catalyze the transfer of a phosphate group from $ATP$ to a hexose sugar (e.g.,glucose).
Option $A$ describes this specific function correctly.
Option $B$ describes $Oxidoreductases$.
Option $C$ describes $Hydrolases$.
Option $D$ is a general description of catabolic processes,often involving $Hydrolases$ or $Lyases$.

(B) The enzyme that catalyzes the hydrolysis of a chemical bond by adding a water molecule $(H_2O)$ is known as a $Hydrolase$.
These enzymes break down complex organic compounds like esters,ethers,peptides,glycosidic bonds,etc.,into simpler molecules.
$Lyases$ catalyze the removal of groups from substrates by mechanisms other than hydrolysis.
$Isomerases$ catalyze the interconversion of optical,geometric,or positional isomers.
$Transferases$ catalyze the transfer of a functional group from one molecule to another.

(C) Maltase is an enzyme that catalyzes the hydrolysis of the disaccharide maltose into two glucose molecules.
Since it involves the addition of water to break a chemical bond,it is classified under the class of enzymes known as Hydrolases.

(A) The correct answer is $A$ (Lyases).
Lyases are enzymes that catalyze the breaking of various chemical bonds by means other than hydrolysis and oxidation,often forming a new double bond or a new ring structure.
They are responsible for the cleavage of $C-C$,$C-O$,$C-N$,and other bonds by elimination,leaving double bonds or rings.
Isomerases catalyze structural rearrangements within a single molecule.
Ligases catalyze the joining of two large molecules by forming a new chemical bond,usually accompanied by the hydrolysis of $ATP$.
Synthetases are a class of ligases that synthesize molecules by coupling the reaction with the hydrolysis of a high-energy phosphate bond.

(A) Enzymes that catalyze the interconversion of optical,geometric,or positional isomers are known as Isomerases.
These enzymes facilitate the rearrangement of atoms within a molecule to form a different isomer without changing the molecular formula.
For example,the conversion of glucose$-6-$phosphate to fructose$-6-$phosphate by phosphoglucose isomerase is a classic reaction catalyzed by an isomerase.

(C) Ligases are enzymes that catalyze the joining of two large molecules by forming a new chemical bond,typically coupled with the hydrolysis of $ATP$.
$Acetyl$ $CoA$ $synthetase$ is a classic example of a ligase because it catalyzes the formation of a bond between acetate and $CoA$ using energy from $ATP$ hydrolysis.
Fructose isomerase is an isomerase,Maltase is a hydrolase,and Aldolase is a lyase.

(B) Aldolase is an enzyme that catalyzes the reversible cleavage of fructose-$1,6$-bisphosphate into glyceraldehyde-$3$-phosphate and dihydroxyacetone phosphate. This reaction involves the breaking of a $C-C$ bond without the use of water or oxidation-reduction. Enzymes that catalyze the removal of groups from substrates by mechanisms other than hydrolysis,leaving double bonds,are classified as Lyases. Therefore,aldolase belongs to the class of Lyases.

(C) Hydrolases are enzymes that catalyze the hydrolysis of a chemical bond.
Hydrolysis is a chemical reaction in which a water molecule $(H_2O)$ is added to break a bond between two molecules.
Therefore,the addition of a water molecule is a characteristic feature of the reaction catalyzed by hydrolases.

(A) Enolase is a metalloenzyme that requires metal ions for its catalytic activity. Specifically,it requires $2$ magnesium ions $(Mg^{2+})$ per subunit to stabilize the substrate and facilitate the conversion of $2$-phosphoglycerate to phosphoenolpyruvate during glycolysis.

(C) Calcium $(Ca^{2+})$ acts as a secondary messenger and regulates many enzymes, often by binding to calmodulin.
$1$. Nitric oxide synthase is regulated by $Ca^{2+}/calmodulin$.
$2$. Protein phosphatase (specifically calcineurin) is regulated by $Ca^{2+}$.
$3$. Adenylate kinase is an enzyme involved in maintaining cellular energy homeostasis by catalyzing the reaction $2ADP \rightleftharpoons ATP + AMP$. It is not regulated by calcium.
$4$. Fructose isomerase (phosphoglucose isomerase) is a glycolytic enzyme and is not regulated by calcium.
However, in the context of standard biochemical regulation, Adenylate kinase is the classic example of an enzyme not dependent on $Ca^{2+}$ signaling for its activity.

(D) Statement $S$ is false because the enzyme that catalyzes the linking of two compounds together is called a Ligase,not a Maltose (which is a disaccharide sugar).
Statement $R$ is true because Isomerases are indeed enzymes that catalyze the inter-conversion of optical,geometric,or positional isomers by rearranging the atoms within the molecule.
Therefore,$S$ is false and $R$ is true.

(D) Enzymes are classified into six classes based on the type of reaction they catalyze.
$1$. Oxidoreductases catalyze oxidation-reduction reactions.
$2$. Transferases catalyze the transfer of a group between substrates.
$3$. Hydrolases catalyze the hydrolysis of bonds.
$4$. Lyases catalyze the removal of groups from substrates by mechanisms other than hydrolysis.
$5$. Isomerases catalyze the interconversion of optical,geometric,or positional isomers.
$6$. Ligases catalyze the linking together of two compounds.
In option $B$,Hexokinase is a transferase because it transfers a phosphate group from $ATP$ to glucose.
In option $D$,Acetyl Co-$A$ synthetase is a ligase because it catalyzes the joining of acetate and Co-$A$ using $ATP$.
However,in standard $NCERT$ classification,Hexokinase is a transferase,but Acetyl Co-$A$ synthetase is also a ligase. Given the options,$B$ and $D$ are both technically correct,but $D$ is a classic example of a ligase in the context of enzyme classification.

(D) Enzymes are biological catalysts that are primarily proteinaceous in nature (except for ribozymes).
They are soluble in water and exist in a colloidal state.
They are required in very small amounts to catalyze biochemical reactions.
However,enzymes are produced by living cells,not non-living cells.
Therefore,the statement that they are secreted from non-living cells is incorrect and inconsistent with their properties.

(C) Nucleic acids that possess catalytic activity and function as enzymes are known as $Ribozymes$. These are typically $RNA$ molecules that can catalyze specific biochemical reactions,such as the cleavage of $RNA$ or $DNA$ molecules or the formation of peptide bonds during protein synthesis.

(D) An enzyme is often composed of a protein part and a non-protein part. The protein portion of an enzyme is called the apoenzyme. The non-protein part is known as the cofactor. Since the apoenzyme is the proteinaceous part of the enzyme,it is made up of amino acids linked by peptide bonds,which are essentially proteins. Therefore,the correct option is $D$.

(C) Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process.
They remain unchanged at the end of the reaction,meaning they can be reused.
Therefore,the statement that 'they are consumed in the reaction' is incorrect and inconsistent with their properties.
Enzymes are indeed specific to their substrates,they exhibit amphoteric properties due to their proteinaceous nature,and they undergo denaturation at high temperatures.

(B) The specific site on an enzyme molecule where the substrate binds to form an enzyme-substrate complex is known as the $Active \ site$.
This site is formed by the specific folding of the polypeptide chain,creating a pocket or groove that is complementary in shape and chemical environment to the substrate molecule.
Therefore,the correct option is $B$.

(C) The lock and key hypothesis,proposed by Emil Fischer,suggests that the active site of an enzyme is rigid and specifically shaped to fit a particular substrate.
When the substrate binds to the active site of the enzyme,it forms a temporary intermediate structure known as the $Enzyme-Substrate$ $(ES)$ complex.
This complex facilitates the conversion of the substrate into products,after which the enzyme is released unchanged.