Biochemistry: Enzymes and Their Functions
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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?

<p>They facilitate the conversion of fibrinogen to fibrin. (C)</p> Signup and view all the answers

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

<p>It facilitates the synthesis of proteins that require y-carboxyglutamate. (C)</p> Signup and view all the answers

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

<p>To facilitate the conversion of substrates into products. (C)</p> Signup and view all the answers

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

<p>They assist enzymes in catalysis by lowering activation energy. (A)</p> Signup and view all the answers

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

<p>The substrate fits into the active site without any alterations. (D)</p> Signup and view all the answers

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

<p>The specificity of the binding site for substrates. (A)</p> Signup and view all the answers

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

<p>Enzymes stabilize the transition state during the reaction. (D)</p> Signup and view all the answers

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

<p>The active site adjusts its shape upon substrate binding. (A)</p> Signup and view all the answers

Which factor does NOT influence the activity of enzymes?

<p>The molecular weight of the enzyme. (C)</p> Signup and view all the answers

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

<p>It stabilizes the positive charge on His57. (A)</p> Signup and view all the answers

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

<p>The oxyanion hole contributes to its stabilization through electrostatic interactions. (C)</p> Signup and view all the answers

What is the consequence of noncompetitive inhibition on enzyme activity?

<p>It reduces the effective concentration of the enzyme available for catalysis. (A)</p> Signup and view all the answers

How does His57 contribute to the reaction mechanism described?

<p>It donates a proton to facilitate the reaction. (C)</p> Signup and view all the answers

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

<p>It leads to the hydrolysis of the peptide bond. (C)</p> Signup and view all the answers

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

<p>It describes the transfer of protons among the catalytic residues. (D)</p> Signup and view all the answers

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

<p>It stabilizes the tetrahedral intermediate through hydrogen bonds. (D)</p> Signup and view all the answers

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

<p>It attacks the acyl-enzyme intermediate to produce a product. (C)</p> Signup and view all the answers

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

<p>It indicates the completion of peptide bond hydrolysis. (B)</p> Signup and view all the answers

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

<p>It is the highest energy state that the substrate passes through. (A)</p> Signup and view all the answers

What unique properties distinguish allosteric enzymes from typical enzymes?

<p>They often have multiple active sites on different protein subunits. (C)</p> Signup and view all the answers

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

<p>It is the negative reciprocal of the x-intercept. (B)</p> Signup and view all the answers

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

<p>It changes the conformation of all active sites, reducing their functionality. (A)</p> Signup and view all the answers

How do allosteric activators influence enzyme function?

<p>They bind to locations other than the active site, increasing active site function. (D)</p> Signup and view all the answers

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

<p>Hexokinase I (B)</p> Signup and view all the answers

What is the effect of cooperativity in allosteric enzymes?

<p>Binding of substrate to one active site increases the likelihood of substrates binding to other active sites. (B)</p> Signup and view all the answers

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

<p>It affects the enzyme regardless of substrate concentration. (C)</p> Signup and view all the answers

What effect does noncompetitive inhibition have on Vmax?

<p>Vmax is reduced for all substrate concentrations. (C)</p> Signup and view all the answers

How does noncompetitive inhibition affect Km?

<p>Km is unchanged. (B)</p> Signup and view all the answers

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

<p>It becomes higher than that of the uninhibited reaction. (B)</p> Signup and view all the answers

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

<p>Sigmoidal dependence. (A)</p> 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?

<p>Histidine. (B)</p> Signup and view all the answers

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

<p>Km increases. (C)</p> Signup and view all the answers

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

<p>Vmax is achieved if enough substrate is present. (A)</p> Signup and view all the answers

Which feature is NOT associated with noncompetitive inhibition?

<p>Km increases. (D)</p> Signup and view all the answers

What provides the mechanism for catalysis in serine protease?

<p>The interaction of the catalytic triad. (D)</p> Signup and view all the answers

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

<p>It accepts a proton from Ser195. (D)</p> Signup and view all the answers

Flashcards

Enzyme Active Site

The specific region of an enzyme where a substrate binds and the chemical reaction occurs.

Enzyme Substrate

The molecule that an enzyme acts upon and converts into a product.

Enzyme Specificity

Enzymes' ability to catalyze only specific reactions or classes of reactions.

Enzyme Cofactor

Non-protein molecules or ions that assist enzymes in their catalytic activity.

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Catalytic Site

The part of an enzyme where the actual chemical reaction occurs.

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Proteolytic Enzyme

Enzymes that catalyze the hydrolysis of peptide bonds between amino acids.

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Enzyme-Substrate Complex

Temporary complex formed when an enzyme binds to its substrate.

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Noncompetitive Inhibition

Enzyme inhibition where the inhibitor binds to a site other than the active site, reducing the enzyme's rate for all substrate concentrations.

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Competitive Inhibition

Enzyme inhibition where the inhibitor competes with the substrate for the active site. Higher substrate concentration is needed to reach the same reaction rate as without the inhibitor.

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Vmax

Maximum rate of an enzyme-catalyzed reaction; reached when all enzyme active sites are saturated with substrate.

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Km

Substrate concentration at which the reaction velocity is half of the maximum velocity (Vmax).

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Active Site

Region on an enzyme where the substrate binds and the catalytic reaction takes place.

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Allosteric Enzyme

Enzyme that changes shape upon binding of a substrate or other effector, affecting its catalytic activity.

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Substrate

The molecule upon which an enzyme acts.

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Protease

Enzyme that catalyzes the hydrolysis of peptide bonds.

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Serine Protease

A type of protease that uses a serine residue in the active site to catalyze the hydrolysis of peptide bonds.

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Catalytic Triad

A set of three amino acid residues in some proteases that work together to catalyze the hydrolysis of peptide bonds.

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Lineweaver-Burk Plot

A graphical representation of enzyme kinetics using the reciprocal of velocity (1/V) and substrate concentration (1/[S]), creating a double-reciprocal plot.

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Km on Lineweaver-Burk

The Michaelis-Menten constant, Km, is determined from the x-intercept of a Lineweaver-Burk plot, representing the substrate concentration at half-maximal velocity.

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Vmax on Lineweaver-Burk

The maximum velocity of an enzyme-catalyzed reaction, Vmax, is determined from the y-intercept of a Lineweaver-Burk plot.

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Allosteric Regulation

Enzyme regulation where a molecule binds to a site other than the active site, affecting enzyme activity.

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Allosteric Enzyme

An enzyme whose activity is regulated by the binding of a molecule to a site other than the active site.

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Allosteric Activator

A molecule that binds to an enzyme away from the active site, increasing enzyme activity.

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Allosteric Inhibitor

A molecule that binds to an enzyme away from the active site, decreasing enzyme activity.

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Cooperativity

Substrate binding to one active site affects activity of other active sites in an enzyme.

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Michaelis-Menten Kinetics

The description of how the substrate concentration affects the rate of an enzyme-catalyzed reaction.

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Noncompetitive Inhibition

A type of enzyme inhibition where the inhibitor binds to an enzyme at a site other than the active site, altering the enzyme's shape and preventing the substrate from binding.

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Catalytic Triad

A group of three amino acid residues (Ser, His, Asp) that work together to catalyze reactions in enzymes like serine proteases.

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Ser195 Oγ

The oxygen atom at the Gamma position of Ser195 (a specific serine amino acid), crucial for forming covalent bonds during the reaction.

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His57

A histidine residue (amino acid) in the catalytic triad, acting as a proton acceptor/donor.

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Asp102

An aspartate residue (amino acid) in the catalytic triad, stabilizing His57 and facilitating the reaction

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Tetrahedral Intermediate

A transient molecule formed during the reaction, involving a temporary four-bonded carbon.

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Acylation

Adding an acyl group to something. In enzymes, the addition of a substrate to the catalytic site.

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Deacylation

Removing the acyl group from something; in enzymes, the removal of the substrate from the catalytic site.

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Oxyanion Hole

A region in an enzyme that stabilizes the negative charge of the tetrahedral intermediate.

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Peptide Bond Hydrolysis

The breaking of a peptide bond in a protein by adding water.

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Prothrombin activation

Prothrombin, a clotting protein, is converted into thrombin, an enzyme that activates the clotting cascade.

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Fibrinogen to Fibrin

Fibrinogen, a blood protein, is cleaved by thrombin to form fibrin, the thread-like protein that forms a blood clot.

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γ-carboxyglutamate role

The γ-carboxyglutamate domain in prothrombin allows binding to calcium, anchoring it to blood cells after injury, positioning it for activation.

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Factor Xa's role in clotting

Factor Xa, a clotting protein, cleaves prothrombin, triggering the conversion to thrombin. It also cleaves fibrinogen.

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Vitamin K's role in clotting

Vitamin K is a vital component in the production of clotting factors, such as prothrombin, by facilitating the addition of carboxyl groups.

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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.

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