Enzymology Basics and Enzyme Kinetics

Questions and Answers

What is the primary function of an enzyme in a biological reaction?

To change the substrate specificity of a reaction

To speed up the rate of a reaction without altering the final equilibrium (correct)

To slow down the rate of a reaction

To alter the final equilibrium between reactants and products

What type of bonds stabilize the structure of an enzyme?

Many weak bonds including H-bonds, electrostatic salt bridges, Van der Waals and hydrophobic interactions (correct)

Ionic bonds

Weak hydrogen bonds

Strong covalent bonds

What is the term for the maximum rate of an enzyme-catalyzed reaction?

Vmax (correct)

Initial velocity

Michaelis-Menten constant

What is the effect of competitive inhibition on the Km value of an enzyme?

Increases the Km value Signup and view all the answers

What is the term for the phenomenon where a substrate binds to an allosteric site, causing a conformational change that affects the active site?

Allosteric modulation Signup and view all the answers

What is the term for the process by which an enzyme is irreversibly inactivated by a molecule?

Irreversible inhibition Signup and view all the answers

What is the equation that describes the kinetics of an enzyme-catalyzed reaction?

Michaelis-Menten equation Signup and view all the answers

What is the term for the initial rate of an enzyme-catalyzed reaction, measured under conditions where the substrate is present in excess?

Initial velocity Signup and view all the answers

What is the main limitation of the lock and key theory proposed by Emil Fisher?

It fails to account for the conformational changes that occur in enzymes during substrate binding. Signup and view all the answers

What is the primary advantage of the induced fit theory over the lock and key theory?

It provides a more accurate description of enzyme-substrate interactions. Signup and view all the answers

What is the role of weak interactions in the induced fit theory?

They initiate the conformational change in the enzyme. Signup and view all the answers

What is the primary function of the induced fit in enzyme catalysis?

To bring specific functional groups into position to catalyze the reaction. Signup and view all the answers

What is the main reason why enzymes are complementary to the transition state of a reaction?

To increase the reaction rate by stabilizing the transition state. Signup and view all the answers

What would happen if the 'Stickase' enzyme were complementary to the metal stick in its ground state?

The reaction rate would decrease because the enzyme stabilizes the ground state. Signup and view all the answers

What is the main consequence of an enzyme stabilizing the transition state of a reaction?

The reaction rate increases because the enzyme reduces the activation energy required for the reaction. Signup and view all the answers

Why is it important for enzymes to be complementary to the transition state of a reaction?

To stabilize the transition state and reduce the activation energy required for the reaction. Signup and view all the answers

What is the rate of an enzyme-catalyzed reaction measured by?

The increase in the amount of product formed per unit time Signup and view all the answers

What is the assumption of the Michaelis-Menten reaction model?

The amount of substrate is much greater than the amount of enzyme Signup and view all the answers

What is the effect of high substrate concentration on the reaction rate of many enzymes?

The reaction rate is independent of the substrate concentration Signup and view all the answers

Which of the following is a characteristic of enzyme kinetics?

Many enzymes display hyperbolic kinetics Signup and view all the answers

What is the function of pepsin?

To break down proteins in the stomach Signup and view all the answers

What is the term for the study of the rate of an enzyme-catalyzed reaction?

Enzyme kinetics Signup and view all the answers

What is the ES complex in the Michaelis-Menten reaction model?

The enzyme-substrate complex Signup and view all the answers

What is the effect of pH on enzyme reactions?

The optimal pH for enzyme activity varies between enzymes Signup and view all the answers

What is the primary function of ligases in biochemical reactions?

To catalyze the formation of new covalent bonds with simultaneous breakdown of ATP Signup and view all the answers

What is the net result of the reaction catalyzed by lactate dehydrogenase?

Conversion of pyruvate to lactate with the reduction of NAD+ Signup and view all the answers

What is the function of transferases in biochemical reactions?

To catalyze the transfer of functional groups from one substance to another Signup and view all the answers

What is the primary function of hydrolases in biochemical reactions?

To catalyze the formation of two products from a substrate by hydrolysis Signup and view all the answers

What is the net result of the reaction catalyzed by trypsin?

Hydrolysis of a peptide bond between two amino acids Signup and view all the answers

What is the primary function of lyases in biochemical reactions?

To catalyze the non-hydrolytic addition or removal of groups from substrates Signup and view all the answers

Which of the following enzymes is an example of an oxidoreductase?

Lactate dehydrogenase Signup and view all the answers

What is the net result of the reaction catalyzed by alanine aminotransferase?

Formation of L-alanine from pyruvate Signup and view all the answers

Which of the following enzymes is an example of a hydrolase?

Trypsin Signup and view all the answers

What is the common feature of all oxidative reactions catalyzed by oxidoreductases?

Transfer of H and O atoms or electrons from one substance to another Signup and view all the answers

What is the assumption behind the Michaelis-Menten equation?

The back reaction of P to S can be ignored Signup and view all the answers

What is the relationship between Km and Vmax when V0 = 0.5Vmax?

Km = Vmax/2 Signup and view all the answers

What is the steady-state assumption in the Michaelis-Menten equation?

The formation of ES is equal to the breakdown of ES Signup and view all the answers

What is the unit of Km?

M Signup and view all the answers

What is the expression for Km in terms of the rate constants?

Km = (k-1 + k2)/k1 Signup and view all the answers

What is the significance of V0 in the Michaelis-Menten equation?

It is the initial velocity of the reaction Signup and view all the answers

What is the condition for the Michaelis-Menten equation to be applicable?

The concentration of product is small Signup and view all the answers

What is the physical significance of the Michaelis-Menten equation?

It describes the kinetics of an enzyme-catalyzed reaction Signup and view all the answers

Study Notes

Enzyme Structure and Properties

Enzymes are proteins composed of one or more polypeptide chains folded into a complex 3-dimensional shape.
Enzyme structure is stabilized by many weak bonds, including hydrogen bonds, electrostatic salt bridges, Van der Waals, and hydrophobic interactions.
Enzymes are biological catalysts that speed up the rate of a reaction without altering the final equilibrium between reactants and products.
Enzymes are extremely efficient, with some enzymes catalyzing reactions at a rate 10^14 times faster than the uncatalyzed reaction.

Enzyme Active Site and Lock-and-Key Theory

The lock-and-key theory, proposed by Emil Fischer in 1884, suggests that enzymes are complementary to their substrate, like a lock and key, to explain the high specificity of enzymes.
However, this theory is misleading, as it does not account for the flexibility of enzymes.
The induced fit theory, proposed by Daniel Koshland in 1958, suggests that enzymes undergo conformational changes upon substrate binding, which brings specific functional groups within the enzyme into the proper position to catalyze the reaction.

Transition State and Enzyme Catalysis

A transition state is an unstable, high-energy intermediate in a chemical reaction.
Stabilizing the transition state is one way that enzymes can speed up a reaction.
Enzymes must be complementary to the transition state to effectively catalyze the reaction.

Enzyme Classification

Enzymes can be classified into six categories based on the type of reaction they catalyze:
- Oxidoreductases (catalyze oxidation/reduction reactions)
- Transferases (catalyze the transfer of functional groups from one substance to another)
- Hydrolases (catalyze the formation of two products from a substrate by hydrolysis)
- Lyases (catalyze non-hydrolytic addition or removal of groups from substrates)
- Ligases (catalyze the formation of new bonds between molecules)

Enzyme Kinetics

The study of the rate of an enzyme-catalyzed reaction and how it varies with different substrate concentrations and the effects of inhibitors.
The reaction rate is the increase in the amount of product formed per unit time or the decrease in the amount of substrate per unit time.
Many enzymes display saturation kinetics, which can be described by the Michaelis-Menten equation.

Michaelis-Menten Equation

The Michaelis-Menten equation describes the rate of an enzyme-catalyzed reaction:
- V0 = Vmax[S] / (Km + [S])
Where V0 is the initial reaction velocity, Vmax is the maximum velocity, Km is the Michaelis constant, and [S] is the substrate concentration.
The Michaelis-Menten equation assumes that the substrate concentration is much higher than the enzyme concentration, and that the initial velocity is used to measure the reaction rate.

Km and [S] Relationship

There is a special relationship between Km and [S] when V0 = 0.5Vmax:
- Km = [S] when V0 = 0.5Vmax

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Description

This quiz covers the fundamental concepts of enzymology, including catalysis, substrate specificity, and the effects of pH and temperature on enzyme-catalyzed reactions.