Enzymes Questions in English

(B) The term "enzyme" was first coined and used by the German physiologist Wilhelm $K\ddot{u}hne$ in $1877$.
He used this term to describe the biological catalysts that were previously referred to as "ferments" in the context of fermentation processes.
Therefore, the correct option is $B$.

(D) The term $zymase$ was coined by $Edward \ Buchner$ in $1897$.
He demonstrated that cell-free extracts of yeast could ferment sugar into alcohol,proving that enzymes (which he called $zymase$) were responsible for fermentation.
Therefore,the correct option is $D$.

(B) All enzymes are proteins,as they are composed of amino acid chains folded into specific three-dimensional structures. However,it is important to note that not all proteins are enzymes. Ribozymes are a notable exception,as they are catalytic $RNA$ molecules,but in the context of general biological classification,enzymes are primarily proteinaceous in nature.

(B) James $B.$ $Sumner$ was the first scientist to isolate and crystallize an enzyme, specifically urease, from jack beans in $1926$. Through his work, he demonstrated that enzymes are composed of proteins, which was a groundbreaking discovery in biochemistry. Therefore, the suggestion that "Enzymes are proteins" is attributed to $Sumner$.

(D) James $B$. Sumner was the scientist who,in $1926$,successfully isolated and purified the enzyme urease in crystalline form from the Jack bean (Canavalia ensiformis). This discovery was significant because it proved that enzymes are proteins,which earned him the Nobel Prize in Chemistry in $1946$.

(C) The correct answer is $C$.
Eduard Buchner $(1897)$,a German chemist,demonstrated that alcoholic fermentation is an enzymatic process.
He proved that a cell-free extract from yeast,which he named $zymase$,has the capability to carry out alcoholic fermentation,thereby showing that living cells are not strictly required for the process,but rather the enzymes within them.

(A) The term $Enzyme$ was coined by $Wilhelm$ $Kuhne$ in $1877$. The first enzymes were discovered in $Yeast$ by $Eduard$ $Buchner$ in $1897$,who demonstrated that cell-free extracts of yeast could ferment sugar into alcohol. This discovery proved that biological catalysts (enzymes) could function outside of living cells.

(C) Most enzymes are proteins,but there are exceptions known as ribozymes (catalytic $RNA$ molecules). Therefore,the statement 'All enzymes are not proteins' is the most accurate,as it acknowledges that while many are proteins,not every single enzyme is a protein.

(C) Enzymes are biological catalysts,also known as biocatalysts.
Most enzymes are globular proteins that accelerate biochemical reactions by lowering the activation energy.
Therefore,they are best defined as protein-catalysts.

(C) The correct answer is $C$. Enzymes are biological catalysts that facilitate various metabolic activities within an organism. Since all living cells of a plant body perform continuous biochemical reactions to maintain life processes,enzymes are present in all living cells of the plant body.

(C) Biological catalysts are substances that increase the rate of chemical reactions within living organisms without being consumed in the process.
These catalysts are known as enzymes.
Most enzymes are proteins that lower the activation energy required for biochemical reactions to occur.

(C) Enzymes are biological catalysts that are primarily composed of proteins. Proteins are long-chain polymers formed by the polymerization of amino acids linked together by peptide bonds. Therefore,enzymes are polymers of amino acids.

(C) The correct answer is $C$.
$1$. While almost all enzymes are proteins,there are exceptions such as ribozymes ($RNA$ molecules that act as enzymes),so the statement 'All enzymes are proteins' is technically a generalization,but 'All proteins are enzymes' is fundamentally incorrect.
$2$. Proteins serve many functions in the body,such as structural support (collagen),transport (hemoglobin),and signaling (hormones),not just catalysis.
$3$. Enzymes are biocatalysts that speed up biochemical reactions.
$4$. Enzymes are generally thermolabile,meaning they can be denatured by heat.

(B) The 'Cascade model' of enzyme regulation,specifically involving $cAMP$ as a second messenger,was proposed by $Earl \ W. \ Sutherland \ Jr.$ in the $1960s$.
$Sutherland$ discovered that $cAMP$ acts as an intracellular signal that triggers a series of enzymatic reactions (a cascade),leading to the activation of enzymes like glycogen phosphorylase.
This discovery earned him the Nobel Prize in Physiology or Medicine in $1971$.

(D) Most enzymes are proteins. Simple proteins are composed only of amino acids. Enzymes like $Amylase$,$Pepsin$,and $Urease$ are examples of enzymes that are composed entirely of amino acids,meaning they are simple proteins. Therefore,none of the options listed are correct as they are all simple proteins.

(B) Enzymes are biological catalysts that speed up chemical reactions within living organisms. In plants,they are essential for regulating various metabolic processes,such as photosynthesis,respiration,and the synthesis of biomolecules. Without enzymes,these vital life-sustaining reactions would occur too slowly to support plant life. Therefore,option $B$ is the correct answer.

(D) The correct answer is $D$.
Enzymes act as biological catalysts that accelerate the rate of biochemical reactions without being consumed in the process.
They are proteinaceous in nature (except for ribozymes) and are highly specific to their substrates.
Since enzymes remain unchanged at the end of the reaction,they are not used up.

(C) Enzymes are biological catalysts that speed up chemical reactions in living organisms.
Almost all enzymes are proteins,which are composed of long chains of amino acids folded into specific three-dimensional shapes.
While most enzymes are proteins,there are exceptions known as ribozymes,which are catalytic $RNA$ molecules.
However,in the context of general biology,the statement that 'they are all proteins' is the most accurate among the given options,as the other options are factually incorrect (enzymes have varying optimal $pH$ and temperature ranges,and they are composed of amino acids,not just being amino acids themselves).

(B) Enzymes are biocatalysts that are primarily proteinaceous in nature,meaning they are composed of amino acid chains.
In contrast,inorganic catalysts are typically metals or simple chemical compounds.
While both enzymes and inorganic catalysts are not consumed in the reaction and speed up the rate of reaction,the proteinaceous nature is a unique characteristic of enzymes that distinguishes them from inorganic catalysts.
Furthermore,enzymes are sensitive to temperature and $pH$ changes,whereas inorganic catalysts often function efficiently at high temperatures and pressures.

(B) An average living cell is a complex biochemical factory. It is estimated that more than $2000$ different types of enzymes are present in a typical living cell to catalyze various metabolic reactions.

(C) The catalytic efficiency of an enzyme is often represented by the $k_{cat}/K_m$ ratio,also known as the specificity constant.
While $K_m$ (Michaelis constant) reflects the affinity of the enzyme for its substrate,it is a key parameter used to compare the efficiency of different enzymes.
$A$ lower $K_m$ value generally indicates a higher affinity of the enzyme for the substrate,which is a primary factor in determining catalytic efficiency under physiological conditions.

(D) An enzyme is a biological catalyst that speeds up chemical reactions in living organisms.
$A$. Insulin is a peptide hormone produced by the pancreas.
$B$. Riboflavin is a vitamin (Vitamin $B_2$).
$C$. Griseofulvin is an antifungal medication.
$D$. Lipase is an enzyme that catalyzes the hydrolysis of fats (lipids).

(B) Enzymes are biological catalysts that are primarily proteinaceous in nature. Proteins are polymers formed by the chemical bonding of amino acids through peptide bonds. Therefore,enzymes are synthesized by linking amino acids together.

(B) Many enzymes are composed of a protein portion and a non-protein portion.
The protein portion of an enzyme is called the $Apoenzyme$.
The non-protein portion is called the $Cofactor$.
When the $Apoenzyme$ and $Cofactor$ are bound together,the complete,catalytically active enzyme is called the $Holoenzyme$.
$Isoenzymes$ are different forms of an enzyme that catalyze the same reaction.

(A) An enzyme consists of a protein part and a non-protein part.
$1$. The protein portion of an enzyme is called the $Apoenzyme$.
$2$. The non-protein portion is referred to as the $Cofactor$.
$3$. When the $Apoenzyme$ and the $Cofactor$ are bound together,the resulting complete,catalytically active enzyme complex is known as the $Holoenzyme$.
Therefore,the correct answer is $A$.

(B) The proteinaceous part of an enzyme is called the $Apoenzyme$.
When the $Apoenzyme$ combines with a non-proteinaceous part (cofactor),the resulting functional enzyme is called the $Holoenzyme$.
Therefore,the correct option is $B$.

(B) Competitive inhibition occurs when the substrate and the inhibitor molecule resemble each other in structure. Due to this structural similarity,both compete for the same active site on the enzyme. If the inhibitor binds to the active site,the enzyme-substrate complex cannot be formed,thus inhibiting the reaction. This type of inhibition can be overcome by increasing the concentration of the substrate,which outcompetes the inhibitor for the active site.

(D) The correct answer is $D$.
Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process.
Statement $A$ is true: Most enzymes are complex globular proteins.
Statement $B$ is true: Enzyme activity is regulated by inhibitors and activators.
Statement $C$ is true: Enzymes have an optimal temperature and $pH$ range; deviations from these can denature the protein.
Statement $D$ is false: Enzymes are not consumed or permanently altered during the reaction; they are regenerated at the end.

(B) Hydrolytic reactions involve the breakdown of chemical bonds by the addition of water $(H_2O)$.
In biological systems,these reactions are typically catalyzed by enzymes (hydrolases).
Because the products of hydrolysis are often chemically stable and the reaction involves a significant increase in entropy,these reactions are generally considered to be irreversible under physiological conditions.

(C) Enzymes are proteins that function within the cellular environment.
Due to their large molecular size and the nature of the cytoplasm,enzymes exist in a colloidal state within the cell.
This colloidal state provides a large surface area for biochemical reactions to occur efficiently.

(C) The $Km$ value (Michaelis-Menten constant) represents the substrate concentration at which the reaction rate is half of the maximum velocity $(V_{max}/2)$.
$A$ lower $Km$ value indicates a higher affinity of the enzyme for its substrate,meaning the enzyme can achieve its maximum catalytic efficiency at lower substrate concentrations.
Therefore,a low $Km$ value is indicative of better enzymatic action and higher substrate affinity.

(D) Enzymes are proteins that possess a complex three-dimensional shape known as the tertiary structure.
This specific three-dimensional folding creates an active site,which is a unique pocket or cleft where the substrate binds.
The specificity of an enzyme is primarily determined by the precise arrangement of amino acids in this tertiary structure,which dictates the shape and chemical environment of the active site,allowing it to bind only to specific substrates.

(A) Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to proceed.
Activation energy is the minimum amount of energy required for the reactant molecules to undergo a chemical transformation.
By providing an alternative reaction pathway with a lower energy barrier,enzymes allow a greater number of substrate molecules to reach the transition state at a given temperature,thereby increasing the rate of the reaction.

$(A)$ The "Lock and Key" hypothesis was proposed by Emil Fischer in $1894$.
According to this theory, the enzyme has a specific geometric shape with an active site that acts like a lock.
The substrate acts as a key that fits perfectly into the active site of the enzyme.
This specific interaction ensures that only the correct substrate can bind to the enzyme to form an enzyme-substrate complex, leading to the reaction.

(C) The "Induced fit" model was proposed by $Daniel \ Koshland$ in $1958$.
This model suggests that the active site of an enzyme is flexible and changes its shape to accommodate the substrate, rather than being a rigid structure as proposed in the earlier "Lock and Key" hypothesis by $Emil \ Fischer$.

(C) $Km$ is the Michaelis-Menten constant. It represents the substrate concentration at which the rate of an enzyme-catalyzed reaction is half of its maximum velocity $(V_{max})$. This constant is a measure of the affinity of an enzyme for its substrate and is fundamentally associated with the formation and dissociation of the enzyme-substrate $(ES)$ complex.

(D) The template theory,also known as the $Lock$ and $Key$ hypothesis,suggests that an enzyme has a specific active site that fits a specific substrate perfectly. The strongest evidence for this theory is that compounds structurally similar to the substrate can bind to the active site,thereby acting as competitive inhibitors. This observation confirms that the enzyme's active site is a rigid template designed for a specific substrate.

(B) Allosteric enzymes are enzymes whose activity is regulated by the binding of an effector molecule at a site other than the active site,known as the allosteric site. In metabolic pathways,this regulation is frequently achieved through feedback inhibition,where the end product of the pathway binds to the allosteric site of an enzyme,thereby inhibiting its activity.

(C) Feedback inhibition is a regulatory mechanism in metabolic pathways where the end product of a series of enzymatic reactions inhibits the activity of an enzyme that acts early in the pathway.
This process prevents the cell from wasting resources by producing excess amounts of a substance that is already present in sufficient quantities.
Therefore,when an enzyme-induced product inhibits the enzymatic activity,it is known as feedback inhibition.

(B) An allosteric enzyme typically possesses at least two distinct sites: the active site,where the substrate binds to undergo catalysis,and the allosteric site (or regulatory site),where an effector molecule binds to regulate the enzyme's activity. Therefore,the correct answer is $B$.

(A) Competitive inhibition occurs when the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme.
Because the inhibitor and the substrate compete for the same active site on the enzyme,this type of inhibition is called competitive inhibition.
Substrate analogues are molecules that mimic the structure of the substrate,allowing them to bind to the active site and prevent the actual substrate from binding.

(A) Succinic dehydrogenase catalyzes the oxidation of succinate to fumarate. Malonic acid is structurally similar to succinate. Because of this structural similarity,malonic acid competes with the substrate (succinate) for the active site of the enzyme succinic dehydrogenase. This type of inhibition,where the inhibitor resembles the substrate and competes for the active site,is known as competitive inhibition.

(B) Competitive inhibitors are structurally similar to the substrate and compete with the substrate for the active site of the enzyme.
Because the inhibitor occupies the active site,the affinity of the enzyme for the substrate decreases.
This results in an increase in the $K_m$ (Michaelis constant) value,which represents the substrate concentration at which the reaction velocity is half of the maximum velocity $(V_{max})$.
However,the $V_{max}$ remains unchanged because high concentrations of substrate can overcome the inhibition.

(D) The correct answer is $D$. Enzymes possess a specific region known as the active site,which is responsible for binding to the substrate and catalyzing the chemical reaction. If the active site is blocked by an inhibitor or a physical obstruction,the enzyme cannot bind to its substrate,thereby rendering the enzyme functionless.

(D) Non-competitive inhibitors are substances that bind to an enzyme at a site other than the active site,known as the allosteric site.
This binding induces a conformational change in the structure of the apoenzyme,which distorts the active site.
As a result,the substrate can no longer bind effectively to the enzyme,rendering the enzyme inactive regardless of the substrate concentration.

(C) The decline in the activity of the enzyme hexokinase by glucose $6$-phosphate is an example of allosteric regulation.
Allosteric enzymes possess a site other than the active site known as the allosteric site.
Substances that bind to these sites to alter the enzyme's activity are called allosteric modulators.
Glucose $6$-phosphate acts as an allosteric inhibitor for hexokinase,binding to the allosteric site and reducing the enzyme's affinity for its substrate,thereby decreasing its activity.

(D) Allosteric enzymes are enzymes that can change their conformational structure upon binding with an effector molecule at a site other than the active site. This change in form allows them to regulate their catalytic activity,which is a key mechanism in metabolic control.

(C) Substrate specificity refers to the ability of an enzyme to choose an exact substrate from a group of similar chemical molecules.
$Sucrase$ is a highly specific enzyme that catalyzes the hydrolysis of only $Sucrose$ into $Glucose$ and $Fructose$.
In contrast,enzymes like $Nuclease$,$Trypsin$,and $Pepsin$ act on a broader range of substrates (e.g.,$Trypsin$ acts on various peptide bonds involving basic amino acids,and $Nuclease$ acts on various phosphodiester bonds in nucleic acids).
Therefore,$Sucrase$ exhibits the highest degree of substrate specificity among the given options.

(C) The correct answer is $C$. The suffix -$ase$ is used in the nomenclature of enzymes. According to the standard convention,enzymes are named by adding the suffix -$ase$ to the name of the substrate upon which they act. For example,the enzyme that acts on lactose is called lactase.

(B) The systematic nomenclature and classification of enzymes were established by the Commission on Enzymes of the International Union of Biochemistry $(IUB)$. According to this system,enzymes are classified into six major classes based on the type of reaction they catalyze,such as oxidoreductases,transferases,hydrolases,lyases,isomerases,and ligases.