Biochemistry: Enzymes and Their Functions

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Questions and Answers

What is the primary role of the gla domain in prothrombin?

It initiates the polymerization of fibrin monomers.

It activates factor Xa during the clotting process.

It enables prothrombin to bind to Ca2+ ions. (correct)

It facilitates the binding of prothrombin to thrombin.

What is the significance of factor Xa in the conversion of prothrombin to thrombin?

It cleaves prothrombin at multiple sites simultaneously.

It cleaves specific peptide bonds in prothrombin to activate it. (correct)

It activates factor Va to enhance thrombin production.

It stabilizes the connection between prothrombin and phospholipid membranes.

Which statement accurately describes the composition of fibrinogen?

It is a small glycoprotein with two subunits.

It contains three non-identical chains: Aα, Bβ, and γ. (correct)

It consists of six identical subunits.

It is composed of three identical polypeptide chains.

What is the function of fibrinopeptides in the clotting process?

They facilitate the conversion of fibrinogen to fibrin. Signup and view all the answers

What role does vitamin K play in the process of blood coagulation?

It facilitates the synthesis of proteins that require y-carboxyglutamate. Signup and view all the answers

What is the primary role of the catalytic site in an enzyme?

To facilitate the conversion of substrates into products. Signup and view all the answers

Which of the following best describes the function of enzyme cofactors?

They assist enzymes in catalysis by lowering activation energy. Signup and view all the answers

How does the lock-and-key model explain enzyme-substrate interaction?

The substrate fits into the active site without any alterations. Signup and view all the answers

What characteristic of enzymes allows them to catalyze highly specific reactions?

The specificity of the binding site for substrates. Signup and view all the answers

Which statement about the transition state in enzyme-catalyzed reactions is correct?

Enzymes stabilize the transition state during the reaction. Signup and view all the answers

What does the induced-fit model propose about the binding of substrates?

The active site adjusts its shape upon substrate binding. Signup and view all the answers

Which factor does NOT influence the activity of enzymes?

The molecular weight of the enzyme. Signup and view all the answers

What is the primary role of Asp102 in the enzymatic process described?

It stabilizes the positive charge on His57. Signup and view all the answers

Which statement about the formation of the tetrahedral intermediate is accurate?

The oxyanion hole contributes to its stabilization through electrostatic interactions. Signup and view all the answers

What is the consequence of noncompetitive inhibition on enzyme activity?

It reduces the effective concentration of the enzyme available for catalysis. Signup and view all the answers

How does His57 contribute to the reaction mechanism described?

It donates a proton to facilitate the reaction. Signup and view all the answers

What is the effect of the proton transfer from water to His57 in the reaction?

It leads to the hydrolysis of the peptide bond. Signup and view all the answers

What is meant by the 'charge relay system' mentioned in the context of the catalytic triad?

It describes the transfer of protons among the catalytic residues. Signup and view all the answers

What is the significance of the oxyanion hole in the enzymatic reaction?

It stabilizes the tetrahedral intermediate through hydrogen bonds. Signup and view all the answers

During deacylation, what role does water play in the enzymatic process?

It attacks the acyl-enzyme intermediate to produce a product. Signup and view all the answers

What is the main effect of the second product formation in the enzymatic reaction?

It indicates the completion of peptide bond hydrolysis. Signup and view all the answers

Which statement describes the transition state in the context of this enzymatic mechanism?

It is the highest energy state that the substrate passes through. Signup and view all the answers

What unique properties distinguish allosteric enzymes from typical enzymes?

They often have multiple active sites on different protein subunits. Signup and view all the answers

In a Lineweaver-Burk plot, how is the Michaelis-Menten constant ($K_M$) determined?

It is the negative reciprocal of the x-intercept. Signup and view all the answers

What effect does an allosteric inhibitor have on an enzyme's active sites?

It changes the conformation of all active sites, reducing their functionality. Signup and view all the answers

How do allosteric activators influence enzyme function?

They bind to locations other than the active site, increasing active site function. Signup and view all the answers

Which of the following enzymes is an example of an allosteric enzyme?

Hexokinase I Signup and view all the answers

What is the effect of cooperativity in allosteric enzymes?

Binding of substrate to one active site increases the likelihood of substrates binding to other active sites. Signup and view all the answers

In the context of enzyme regulation, what defines noncompetitive inhibition?

It affects the enzyme regardless of substrate concentration. Signup and view all the answers

What effect does noncompetitive inhibition have on Vmax?

Vmax is reduced for all substrate concentrations. Signup and view all the answers

How does noncompetitive inhibition affect Km?

Km is unchanged. Signup and view all the answers

In competitive inhibition, what change occurs in the required substrate concentration to achieve one-half Vmax?

It becomes higher than that of the uninhibited reaction. Signup and view all the answers

What characteristic of allosteric enzymes is described by their reaction velocity dependence on substrate concentration?

Sigmoidal dependence. Signup and view all the answers

Which amino acid is noted for its role in the His57 and Ser195 interaction within the serine protease catalytic triad?

Histidine. Signup and view all the answers

What is the primary consequence of a competitive inhibitor on the Michaelis-Menten constant (Km)?

Km increases. Signup and view all the answers

In the presence of sufficient substrate for a competitive inhibitor, what is the effect on Vmax?

Vmax is achieved if enough substrate is present. Signup and view all the answers

Which feature is NOT associated with noncompetitive inhibition?

Km increases. Signup and view all the answers

What provides the mechanism for catalysis in serine protease?

The interaction of the catalytic triad. Signup and view all the answers

What is the primary role of His57 in the catalytic action of serine proteases?

It accepts a proton from Ser195. Signup and view all the answers

Study Notes

Enzymes as Remarkable Catalysts

Enzymes speed up important biochemical reactions
Most enzymes are proteins, some are RNA
Enzymes stabilize the transition state (highest energy species in reaction pathway)
Work in specific temperature and pH ranges

Enzyme Catalyzed Reactions

Reactants in enzyme catalyzed reactions are called substrates.
Enzymes are highly specific. Examples are proteolytic enzymes that catalyze the hydrolysis of peptide bonds connecting amino acids.

The Active Sites of Enzymes

Enzymes generally have two sites: catalytic and binding sites.
The catalytic site is where the chemical reaction occurs.
The binding site (often called the active site) is where the substrate binds to the enzyme, creating an enzyme-substrate complex. This binding is highly specific.

Cofactors and Enzyme Activity

Enzyme cofactors (non-protein molecules or ions) assist enzymes in catalysis (chemical reaction acceleration).
Coenzymes and metals are two types of cofactors
An enzyme with its cofactor is called a holoenzyme, without it, the enzyme is called an apoenzyme.

Enzyme Kinetics

The change in free energy (ΔG) of a reaction depends only on difference in free energy between reactants and products.
ΔG does not provide information about the rate of the reaction.
Enzymes increase the rate of a reaction by lowering the activation energy but do not change the equilibrium constant.

Michaelis-Menten Kinetics

Plot of reaction velocity (Vo) against substrate concentration ([S]) shows maximal velocity (Vmax) is approached asymptotically.
Michaelis constant (KM) is the substrate concentration achieving half-maximal velocity(Vmax/2)
Most enzymes display Michaelis-Menten kinetics

Allosteric Regulation

Allosteric regulation involves a regulatory molecule binding to an enzyme at a site other than the active site (allosteric site).
This may involve noncompetitive inhibition, and/or competitive inhibition and/or cooperativity.
Some allosteric enzymes show cooperative substrate binding and a sigmoidal curve.

Competitive Inhibition

Inhibitor is similar in structure to the substrate and competes with the substrate for binding to the active site.
Reaction is slowed/prevented
KM increases, but Vmax remains the same.

Non-Competitive Inhibition

Inhibitor binds to a site on the enzyme other than the active site (allosteric site)
Inhibitor and substrate can both bind simultaneously to the enzyme
Reaction is slowed/prevented
KM remains the same, but Vmax decreases.

Proteases

Proteases are enzymes that cleave peptide bonds.
The mechanism involves a catalytic triad of amino acid residues.
His57, Asp102, and Ser195 are crucial for function.

Blood Clotting

Clotting factors (proteins) are inactive zymogens that become active enzymes via proteolysis
The activation process involves intrinsic and extrinsic pathways converging on a common pathway.
Factors include FIX, FVII, FX, and FII.
Thrombin converts fibrinogen to fibrin, forming a clot.
Vitamin K is a crucial cofactor in this process.

Classification of Enzymes

Enzymes are classified into 6 basic groups based on the reaction they catalyze.
Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, and Ligases.

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Description

Explore the fascinating world of enzymes in this quiz focusing on their role as catalysts in biochemical reactions. Learn about their structure, active sites, and the significance of cofactors in enzyme activity. Test your understanding of how these remarkable proteins facilitate life-sustaining processes.