Enzymes

Question 1

Describe the role of enzymes in biological reactions.

Answer 1

Enzymes are highly specific protein catalysts that increase the rates of chemical reactions in the body, directing metabolic events by selectively enhancing useful biological reactions.

Question 2

Define thermodynamics in the context of chemical reactions.

Answer 2

Thermodynamics tells us which way and how far a reaction will eventually go, quantified by equilibrium constants (K_eq) that indicate the direction of a reaction.

Question 3

How is the equilibrium constant (K_eq) calculated for a reaction?

Answer 3

For a reaction A + B <-> C + D, K_eq is calculated as K_eq = ([C][D]/[A][B]) at equilibrium.

Question 4

Discuss the significance of Gibbs free energy (ΔG) in chemical reactions.

Answer 4

Gibbs free energy (ΔG) indicates the spontaneity of a reaction; a reaction is thermodynamically favorable if ΔG < 0, and it is in equilibrium if ΔG = 0.

Question 5

What is the relationship between ΔG and reaction spontaneity?

Answer 5

A reaction is spontaneous if ΔG is less than zero (ΔG < 0) and reaches equilibrium when ΔG equals zero (ΔG = 0).

Question 6

Describe the characteristics of enzyme substrates.

Answer 6

Enzyme substrates reversibly bind to the active sites of enzymes, where they are converted into products.

Question 7

How do cofactors affect enzyme activity?

Answer 7

Some enzymes require the binding of nonprotein cofactors to be active; organic cofactors are referred to as coenzymes.

Question 8

Explain the concept of reaction kinetics.

Answer 8

Kinetics tells us how fast a reaction will go and how quickly it will reach equilibrium, providing insight into the rate of a reaction.

Question 9

What does a K_eq value less than 1 indicate about a reaction?

Answer 9

If K_eq < 1, it indicates that the reaction will favor the formation of reactants rather than products.

Question 10

Describe the equation for Gibbs free energy under nonstandard conditions.

Answer 10

The Gibbs free energy under nonstandard conditions is defined as ΔG = ΔG°’ + RTlnQ, where Q is the reaction quotient.

Question 11

How does the magnitude of K_eq reflect a reaction’s progress?

Answer 11

The magnitude of K_eq reflects how far a reaction will eventually go under standard conditions; a higher K_eq indicates a greater extent of reaction towards products.

Question 12

What is the effect of a 10-fold increase in Q on ΔG?

Answer 12

For each 10-fold increase in Q, the Gibbs free energy (ΔG) increases by a certain amount, indicating a shift in the reaction’s favorability.

Question 13

Discuss ways in which enzyme activity may be regulated.

Answer 13

Enzyme activity can be regulated through various mechanisms, including the binding of inhibitors or activators, changes in environmental conditions, and the presence of cofactors.

Question 14

Describe how thermodynamically unfavorable reactions can proceed.

Answer 14

Thermodynamically unfavorable reactions can proceed by coupling them to thermodynamically favorable reactions directly or via a high-energy compound.

Question 15

Define the role of kinetics in chemical reactions.

Answer 15

Kinetics tells you how fast a reaction will go, and it is quantified by rate constants (k).

Question 16

How is the rate constant (k) related to activation energy (E a)?

Answer 16

The rate constant (k) is related to the activation energy (E a) for the reaction, influencing the speed of the reaction.

Question 17

What does the activation energy barrier (E a) represent?

Answer 17

The activation energy barrier (E a) represents the difference in energy between the reactant and the high-energy intermediate (transition state) formed during the conversion of reactant to product.

Question 18

Describe the Michaelis-Menten model in enzymatic reactions.

Answer 18

The Michaelis-Menten model states that the reaction rate (V) equals V max ([S]/([S] + K M)), where V max is the maximal reaction rate at enzyme saturation and K M is the substrate concentration required to achieve V max/2.

Question 19

How can enzymatic activity be altered?

Answer 19

Enzymatic activity can be altered by inhibitors, effector molecules, covalent modifications, or by changing the amount of enzyme present.

Question 20

Define competitive inhibitors and their effect on enzyme kinetics.

Answer 20

Competitive inhibitors bind to the active site of an enzyme, competing with the substrate, which increases K M but does not affect V max.

Question 21

What are noncompetitive inhibitors and how do they affect enzyme activity?

Answer 21

Noncompetitive inhibitors bind to a different part of the enzyme than the substrate, not affecting substrate binding, and they decrease V max without changing K M.

Question 22

Explain the concept of allosteric enzymes.

Answer 22

Allosteric enzymes can be conformationally altered by effector molecules, usually contain multiple subunits, and catalyze the committed step early in a metabolic pathway.

Question 23

How can covalent modification regulate enzyme activity?

Answer 23

Covalent modification, such as phosphorylation, can regulate enzyme activity by altering the enzyme’s structure and function.

Question 24

What is the significance of changing the amount of enzyme present in a cell?

Answer 24

Changing the amount of enzyme present can alter the overall enzymatic activity and influence metabolic pathways.

Question 25

Describe the role of alcohol dehydrogenase in methanol metabolism.

Answer 25

Alcohol dehydrogenase converts methanol to formaldehyde, which is toxic to cells. Ethanol competes with methanol for the active site of alcohol dehydrogenase, slowing formaldehyde production and allowing the body to excrete methanol through other pathways.

Question 26

How does the change in free energy (ΔG) relate to the direction of a reaction?

Answer 26

The change in free energy (ΔG) indicates the direction of a reaction. A negative ΔG suggests the reaction will proceed forward, while a positive ΔG indicates it will proceed in reverse.

Question 27

Explain the difference between competitive and noncompetitive inhibitors.

Answer 27

Competitive inhibitors bind to the active site, increasing Km but not affecting Vmax. Noncompetitive inhibitors bind elsewhere, leaving Km unchanged but decreasing Vmax.

Question 28

How does substrate concentration affect competitive inhibitors?

Answer 28

At high substrate concentrations, competitive inhibitors can be ‘driven out’ of the active site by substrate molecules, allowing Vmax to remain the same as in the absence of the inhibitor.

Question 29

What is the significance of the Gibbs free energy (ΔG) in biochemical reactions?

Answer 29

Gibbs free energy (ΔG) is significant as it determines the spontaneity of a reaction; negative values indicate a spontaneous reaction, while positive values indicate non-spontaneity.

Question 30

Describe the relationship between the equilibrium constant (Keq) and reaction direction.

Answer 30

The equilibrium constant (Keq) indicates the ratio of products to reactants at equilibrium; a Keq greater than 1 favors products, while a Keq less than 1 favors reactants.

Question 31

What is the effect of noncompetitive inhibitors on Vmax?

Answer 31

Noncompetitive inhibitors decrease Vmax because they prevent the enzyme from catalyzing the reaction efficiently, regardless of substrate concentration.

Question 32

Define Michaelis-Menten kinetics in the context of enzyme activity.

Answer 32

Michaelis-Menten kinetics describes the rate of enzymatic reactions by relating reaction rate to substrate concentration, characterized by parameters Km and Vmax.

Question 33

How does the turnover number relate to enzyme efficiency?

Answer 33

The turnover number indicates how many substrate molecules an enzyme converts to product per unit time, reflecting the enzyme’s efficiency.

Question 34

Explain the concept of transition state in enzyme catalysis.

Answer 34

The transition state is a high-energy state during the conversion of substrates to products in an enzymatic reaction, where bonds are being formed and broken.

Question 35

What role do cofactors play in enzyme function?

Answer 35

Cofactors are non-protein molecules that assist enzymes in catalyzing reactions, often by stabilizing the enzyme-substrate complex or participating in the reaction.