Enzymes Flashcards
Describe the role of enzymes in biological reactions.
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.
Define thermodynamics in the context of chemical reactions.
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.
How is the equilibrium constant (K_eq) calculated for a reaction?
For a reaction A + B <-> C + D, K_eq is calculated as K_eq = ([C][D]/[A][B]) at equilibrium.
Discuss the significance of Gibbs free energy (ΔG) in chemical reactions.
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.
What is the relationship between ΔG and reaction spontaneity?
A reaction is spontaneous if ΔG is less than zero (ΔG < 0) and reaches equilibrium when ΔG equals zero (ΔG = 0).
Describe the characteristics of enzyme substrates.
Enzyme substrates reversibly bind to the active sites of enzymes, where they are converted into products.
How do cofactors affect enzyme activity?
Some enzymes require the binding of nonprotein cofactors to be active; organic cofactors are referred to as coenzymes.
Explain the concept of reaction kinetics.
Kinetics tells us how fast a reaction will go and how quickly it will reach equilibrium, providing insight into the rate of a reaction.
What does a K_eq value less than 1 indicate about a reaction?
If K_eq < 1, it indicates that the reaction will favor the formation of reactants rather than products.
Describe the equation for Gibbs free energy under nonstandard conditions.
The Gibbs free energy under nonstandard conditions is defined as ΔG = ΔG°’ + RTlnQ, where Q is the reaction quotient.
How does the magnitude of K_eq reflect a reaction’s progress?
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.
What is the effect of a 10-fold increase in Q on ΔG?
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.
Discuss ways in which enzyme activity may be regulated.
Enzyme activity can be regulated through various mechanisms, including the binding of inhibitors or activators, changes in environmental conditions, and the presence of cofactors.
Describe how thermodynamically unfavorable reactions can proceed.
Thermodynamically unfavorable reactions can proceed by coupling them to thermodynamically favorable reactions directly or via a high-energy compound.
Define the role of kinetics in chemical reactions.
Kinetics tells you how fast a reaction will go, and it is quantified by rate constants (k).
How is the rate constant (k) related to activation energy (E a)?
The rate constant (k) is related to the activation energy (E a) for the reaction, influencing the speed of the reaction.
What does the activation energy barrier (E a) represent?
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.
Describe the Michaelis-Menten model in enzymatic reactions.
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.
How can enzymatic activity be altered?
Enzymatic activity can be altered by inhibitors, effector molecules, covalent modifications, or by changing the amount of enzyme present.
Define competitive inhibitors and their effect on enzyme kinetics.
Competitive inhibitors bind to the active site of an enzyme, competing with the substrate, which increases K M but does not affect V max.
What are noncompetitive inhibitors and how do they affect enzyme activity?
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.
Explain the concept of allosteric enzymes.
Allosteric enzymes can be conformationally altered by effector molecules, usually contain multiple subunits, and catalyze the committed step early in a metabolic pathway.
How can covalent modification regulate enzyme activity?
Covalent modification, such as phosphorylation, can regulate enzyme activity by altering the enzyme’s structure and function.
What is the significance of changing the amount of enzyme present in a cell?
Changing the amount of enzyme present can alter the overall enzymatic activity and influence metabolic pathways.
