Lecture 4 Flashcards
Metabolism and Enzymes
What is free energy?
Free energy (G) is the amount of energy available to do work in a system.
What is an exergonic reaction?
An exergonic reaction is spontaneous and releases energy (ΔG < 0).
What is an endergonic reaction?
An endergonic reaction is non-spontaneous and requires energy input (ΔG > 0).
How can endergonic reactions be coupled to exergonic reactions?
Cells couple exergonic reactions (which release energy) to endergonic reactions to make them occur by transferring energy.
How does ATP hydrolysis drive endergonic reactions?
ATP hydrolysis releases free energy, which is used to power energy-consuming processes in the cell.
What is the transition state in a chemical reaction?
The transition state is an unstable, high-energy intermediate between reactants and products.
What do energy diagrams show in a chemical reaction?
They show the energy levels of reactants, transition states, and products.
How do catalysts (including enzymes) affect reaction rates?
They lower the activation energy and speed up both forward and reverse reactions without being consumed.
How do enzymes affect reaction equilibrium?
Enzymes speed up reactions but do not change the equilibrium position of reactants and products.
Why is enzyme activity low at low temperatures?
At low temperatures, molecules move slower, reducing collisions and enzyme efficiency.
Why is enzyme activity low at high temperatures?
High temperatures can denature enzymes, disrupting their shape and function.
Why is enzyme activity low when pH is too low?
Low pH can alter the enzyme’s charge, affecting substrate binding and folding.
Why is enzyme activity low when pH is too high?
High pH can disrupt hydrogen bonds and ionic interactions, leading to loss of function.
What is a competitive inhibitor?
A molecule that resembles the substrate and binds to the active site, blocking substrate binding.
How does a competitive inhibitor affect enzyme function?
It competes with the substrate, increasing KM but not affecting Vmax.
What is a non-competitive inhibitor?
A molecule that binds to an allosteric site, changing enzyme shape and reducing function.
How does a non-competitive inhibitor affect enzyme function?
It reduces Vmax without changing KM because it does not compete with the substrate.
What is a Michaelis-Menten plot?
A graph that shows reaction velocity (V) vs. substrate concentration ([S]).
What is on the x-axis of a Michaelis-Menten plot?
Substrate concentration ([S]).
What is on the y-axis of a Michaelis-Menten plot?
Reaction velocity (V).
How do you identify a competitive inhibitor on a Michaelis-Menten plot?
A competitive inhibitor increases KM but does not change Vmax.
How do you identify a non-competitive inhibitor on a Michaelis-Menten plot?
A non-competitive inhibitor decreases Vmax but does not change KM.
What does Vmax tell you?
Vmax is the maximum reaction rate when the enzyme is saturated with substrate.
What does KM tell you?
KM is the substrate concentration at which the reaction velocity is half of Vmax, indicating enzyme affinity for the substrate.
