L10- Enzymes as Catalysts Flashcards
What enzyme catalyzes the hydrolysis of peptides on the C-terminal side of phenylalanine, tyrosine and tryptophan?
Chymotrypsin.
What amino acids make up the catalytic triad in a serine protease?
Aspartate, histidine and serine.
Do enzymes change their structure after catalysis?
No. At the end of the reaction cycle they are the same as when they started.
When the Gibbs free energy (G) of a reaction is negative, that reaction is ______.
Spontaneous.
When the Gibbs free energy (G) of a reaction is positive, that reaction is ______.
Non-spontaneous.
When the Gibbs free energy (G) of a reaction is zero, that reaction is ______.
At equilibrium.
True or False. All exothermic reactions are spontaneous.
False. Delta G can be negative (indicating a spontaneous reaction) even when delta H is positive. This occurs when delta S (the change in entropy) is positive.
True or False. Reactions in the body are in equilibrium.
False.
How do enzymes affect the energy of reactions?
Enzymes lower the activation energy. They accelerate the rate of reactions, but do not change the potential energy of the substrates or products.
How does the activation energy affect the speed of a reaction?
In general, the larger the activation energy the slower the reaction.
Define catabolism.
Burning fuel to make ATP.
Define anabolism.
Burning energy (usually ATP) for biosynthetic processes, active transport and/or mechanical work.
How can one determine reaction velocity?
By measuring the amount of product formed per unit time.
What kinetic parameters can be extracted from a Michaelis-Menten kinetics graph?
Vmax, the maximum velocity of the catalyzed reaction, and Km, the substrate concentration required to achieve half the maximum velocity.
When is Km equal to the substrate concentration in a Michaelis-Menten Kinetics graph?
When the substrate concentration is at half of Vmax.
Delta G for ATP hydrolysis (ATP + H2O -> ADP + Pi) is -7.3 kcal/mole. How much energy is required to perform the reverse reaction?
+7.3 kcal/mole.
What is a cofactor?
Cofactors are typically small molecules that help promote catalysis. Many vitamins act as cofactors.
Which enzyme is deficient in individuals with methylmalonic acidemia?
Methylmalonyl mutase.
What is the cofactor for methylmalonyl mutase?
Vitamin B12.
What are the substrates and products of methylmalonyl mutase?
The enzyme converts methylmalonyl CoA to succinyl CoA.
True or False. Generally, the atoms in an enzyme that bind to a substrate are different than the atoms that participate in the catalysis of a reaction.
True.
What are the four steps, in order, of a reaction catalyzed by serine proteases?
- Binding of substrate, 2. attack by serine, 3. stabilization of transition state, and 4. release of products.
What is an oxyanion hole and what is its function?
It is a structural pocket in an enzyme that stabilizes an oxyanion (i.e. stabilizes the transition state).
The initial enzyme velocity proportional to what?
The amount of substrate.
The y-intercept in Lineweaver-Burk plots corresponds to what kinetic parameter?
NAME?
The x-intercept in Lineweaver-Burk plots corresponds to what kinetic parameter?
NAME?
The slope in Lineweaver-Burk plots corresponds to what kinetic parameter?
Km/Vmax.
