Enzymology Basics: Catalysis and Kinetics

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Questions and Answers

Which type of enzyme catalyzes the transfer of a functional group from one substance to another?

Transferases (correct)

Hydrolases

Oxidoreductases

Isomerases

What is the result of the action of hydrolases on a substrate?

Formation of a single product from two substrates

Formation of two products from a substrate (correct)

Isomerization of a single molecule

Transfer of a functional group from one substance to another

Which type of enzyme is responsible for the cleavage of amino terminal amino acid from a tripeptide?

Oxidoreductases

Tripeptide aminopeptidase

Hydrolases (correct)

Lyases

What is the primary function of oxidoreductases?

To catalyze oxidation/reduction reactions Signup and view all the answers

What type of bond is cleaved by lyases?

C-C, C-N, C-O, or C-S bonds Signup and view all the answers

Which type of enzyme is responsible for the intramolecular rearrangement of a single molecule?

Isomerases Signup and view all the answers

What is the primary function of biological catalysts?

To speed up the rate of a reaction Signup and view all the answers

What type of bonds stabilize the 3-dimensional structure of enzymes?

Many weak bonds, including H-bonds, electrostatic salt bridges, Van der Waals, and hydrophobic interactions Signup and view all the answers

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

Increases the Km value Signup and view all the answers

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

Vmax Signup and view all the answers

What is the type of inhibition that involves the binding of an inhibitor to a site other than the active site?

Non-competitive inhibition Signup and view all the answers

What is the term for the ability of an enzyme to bind multiple molecules of substrate simultaneously?

Cooperativity Signup and view all the answers

What is the effect of an enzyme on the activation energy of a reaction?

Decreases the activation energy Signup and view all the answers

What is the term for the binding of a substrate to an enzyme, where the shape of the substrate fits the shape of the active site?

Lock and key theory Signup and view all the answers

What type of bond is formed when a ligase catalyzes a reaction?

C-O bond Signup and view all the answers

What is the effect of increasing temperature on an enzyme's structure?

The enzyme's structure becomes disorganized and it becomes inactive Signup and view all the answers

What is the effect of changes in pH on an enzyme's active site?

The active site's ionization state changes, affecting substrate binding Signup and view all the answers

Which type of enzyme catalyzes an isomerization reaction?

Isomerase Signup and view all the answers

What is the effect of pH changes on an enzyme's substrate binding affinity?

The substrate binding affinity changes due to changes in Km Signup and view all the answers

What is the result of an enzyme's weak bonds being broken?

The enzyme's structure becomes disorganized and it becomes inactive Signup and view all the answers

What was the major limitation of Emil Fisher's lock and key theory?

It did not consider the conformational changes in enzymes during substrate binding. Signup and view all the answers

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

To bring specific functional groups within the enzyme in the proper position to catalyse the reaction. Signup and view all the answers

What is the significance of the transition state in enzyme catalysis?

It is the intermediate state with high energy and instability. Signup and view all the answers

Why is complementarity of enzymes to the transition state necessary?

To stabilize the transition state and speed up the reaction. Signup and view all the answers

What is the main difference between the lock and key theory and the induced fit theory?

The lock and key theory involves a static enzyme conformation, while the induced fit theory involves dynamic conformational changes. Signup and view all the answers

What is the consequence of an enzyme being complementary to the substrate, but not to the transition state?

The enzyme will not improve the reaction rate. Signup and view all the answers

What is the significance of the 'Stickase' example in understanding enzyme catalysis?

It highlights the limitations of the lock and key theory. Signup and view all the answers

What is the outcome of the induced fit in terms of enzyme conformation?

The enzyme conformation changes to enhance catalytic properties. Signup and view all the answers

What is the primary focus of the study of enzyme kinetics?

The variation of reaction rate with different substrate concentrations Signup and view all the answers

Which of the following is a characteristic of an enzyme-catalyzed reaction with a 'hyperbolic' kinetics?

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

What is the definition of reaction rate in an enzyme-catalyzed reaction?

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

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

[S] >> [E] so that the amount of substrate bound by enzyme is small Signup and view all the answers

What is the role of pepsin in the stomach?

To function as an enzyme in acidic conditions Signup and view all the answers

What is the relationship between reaction rate and substrate concentration at low substrate concentrations in an enzyme-catalyzed reaction with 'hyperbolic' kinetics?

The reaction rate is directly proportional to substrate concentration 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 enzyme-substrate complex in the Michaelis-Menten reaction model?

The intermediate state where the enzyme is bound to the substrate Signup and view all the answers

Study Notes

Enzyme Structure

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, such as H-bonds, electrostatic salt bridges, Van der Waals, and hydrophobic interactions.
Catalase has four identical subunits, each with catalytic activity.

Definition and Properties of Enzymes

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 the enzyme catalase catalyzing the breakdown of its substrate H2O2 to water at a rate 10^14 times faster than the uncatalysed reaction at 30°C.

Effect of Enzymes on Activation Energy

Enzymes lower the activation energy of a reaction.

Lock and Key Theory

Emil Fischer proposed the lock and key theory in 1884, suggesting that enzymes are complementary to their substrate, like a lock and key, to explain the high specificity of enzymes.
However, this theory is misleading and has been modified by the induced fit theory.

Induced Fit Theory

Daniel Koshland suggested that enzymes undergo conformational changes upon substrate binding, induced by weak interactions with the substrate itself.
These changes can affect residues in the active site, and the "induced fit" serves to bring specific functional groups within the enzyme in the proper position to catalyze the reaction.

Transition State

A transition state is an unstable, high-energy intermediate in a chemical reaction.
Enzymes can speed up a reaction by stabilizing the transition state.

Classification of Enzymes

Enzymes are classified into six categories:
- Oxidoreductases: catalyze oxidation/reduction reactions, transfer of H and O atoms or electrons from one substance to another.
- Transferases: catalyze the transfer of a functional group 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.
- Isomerases: catalyze intramolecular rearrangement, or isomerization changes within a single molecule.
- Ligases: catalyze the joining of two molecules by the synthesis of new C-O, C-S, C-N, or C-C bonds with simultaneous breakdown of ATP.

Effects of Temperature and pH on Enzyme-Catalysed Reactions

Temperature: Enzyme structure is stabilized by weak bonds, which are easily broken by heat, leading to a disorganized or tangled structure and loss of catalytic activity.
pH: Changes in pH can affect the rate of enzyme-catalysed reactions, with direct effects on the rate equation, substrate effects, and effects on the enzyme itself.

Enzyme Kinetics

Enzyme kinetics is the study of the rate of an enzyme-catalysed reaction, including the effects of substrate concentration and inhibitors.
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.

Michaelis-Menten Reaction Model

The Michaelis-Menten reaction model is a kinetic model that describes the rate of enzyme-catalysed reactions.
The model assumes that the substrate binds to the enzyme, forming an enzyme-substrate complex, which then breaks down to form the product and release the enzyme.

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Description

Review the fundamentals of enzymology, including catalysis, substrate specificity, and the effects of pH and temperature on enzyme reactions. Describe how the rate of an enzyme reaction depends on substrate concentration and other factors.