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Example Questions
Example Question #51 : Enzyme Kinetics And Inhibition
The term that describes an enzyme's active site as one that undergoes a conformational change upon the binding of a substrate is known as __________.
the induced fit model
cooperative binding
the active site model
the lock and key hypothesis
affinity dependent binding
the induced fit model
The question describes the "induced fit model", in which the binding of a substrate induces an actual change in the shape of the enzyme in order for the substrate to fit properly. This models differs from "the lock and key hypothesis" and "the active site model" (which are actually the same thing, and describes an enzyme and its substrate as fitting perfectly together). Cooperative binding is a concept that refers to binding becoming easier for subsequent molecules in comparison to previous molecules (the sixth molecule binds more readily than the fifth, which binds more readily than the fourth, etc.). Finally, affinity dependent binding is not a real term used in biochemistry (all binding is related to affinity anyway).
Example Question #52 : Enzyme Kinetics And Inhibition
All of the following are false regarding catalysts except __________.
that they lower the Ea (activation energy) of a reaction
that they change the of a reaction.
All of the other choices are false statements regarding catalysts.
that they can make non-spontaneous reactions occur.
that they are consumed and not regenerated in a reaction.
that they lower the Ea (activation energy) of a reaction
A catalyst works to speed up a reaction by lowering the Ea (activation energy), which is related to chemical kinetics. A catalyst has nothing to do with thermodynamics, and can neither change the of a reaction, nor make a non-spontaneous one occur.
Additionally, by definition a catalyst is not consumed in a reaction, and it is regenerated after the reaction occurs. This allows for the possibility of a catalyst having an enormous impact on the rate of a reaction, as it is can once again exert its effects after being regenerated.
Example Question #13 : Fundamentals Of Enzyme Kinetics
A 21-year-old man was brought to the emergency room by his fraternity brothers. He is known to be a chronic and uncontrolled alcoholic and has been drinking whiskey for the past 7 days when his friend found him in the hotel semicomatose. Bloodwork confirmed acidosis and a low blood glucose level. Which of the following reactions is increased, contributing to both his hypoglycemia and acidosis?
The most important concept about chronic alcoholism is based off the fact that the increased ratio of from alcohol metabolism interferes with gluconeogenesis; 2) the conversion of pyruvate to lactate is favored, decreasing gluconeogenesis and increasing blood lactate. Pyruvate dehydrogenase, the enzyme that catalyzes the conversion of pyruvate to lactate. The conversion of pyruvate to acetyl-CoA, catalyzed by alanine aminotransferase, does not require and is not directly affected by this ratio. An increase in pyruvate to oxaloacetate (catalyzed by pyruvate carboxylase), is a reaction used in gluconeogenesis. If increased, it would favor this process or stimulate the citric acid cycle.
Example Question #53 : Enzyme Kinetics And Inhibition
Insulin is released when the body is in a well-fed state. Insulin stimulates which of the following?
Fatty acid degradation only
Fatty acid degradation and uptake of glucose
Glycogen synthesis only
Uptake of glucose and Glycogen synthesis
Uptake of glucose and Glycogen synthesis
When the body is in a well fed state, insulin stimulates glycolysis (glucose uptake) and the first step to convert glucose to glucose-6-phosphatase. When you have an increase of insulin, it stimulates protein phosphatase (PP1), which stimulates synthase while inhibiting phosphorylase. This leads to a decreased conversion of glycogen to glucose. Gluconeogeneisis occurs in the starvation state as well as fatty acid degradation.
Example Question #54 : Enzyme Kinetics And Inhibition
A reaction that is directly proportional to the reactant concentration is considered to be which of the following?
Zeroth order reaction
Second order reaction
Third order reaction
Bimolecular reaction
First order reaction
First order reaction
A first order reaction is one in which the amount of product is dependent on only one reactant. For instance:
The above reaction is first order because the amount of product produced depends solely on the concentration of A. Therefore, a first order reaction is one in which the reaction is directly proportional to the reactant concentration.
Note: bimolecular reaction and second order reaction are synonymous.
Example Question #55 : Enzyme Kinetics And Inhibition
Which of the following is true of a molecule that binds to the allosteric site of an enzyme?
The molecule will always cause a change in the shape of the enzyme to enhance its catalytic activity on the substrate
The molecule will cause a conformational change which will affect the regulatory effects of the enzyme
The molecule must have a similar molecular structure to that of the enzyme's substrate
The molecule will always cause a change in the shape of the enzyme to inhibit its catalytic activity on the substrate
The molecule will always bind to the enzyme, but will cause no change in the catalytic activity of the enzyme
The molecule will cause a conformational change which will affect the regulatory effects of the enzyme
A molecule that binds to an allosteric site on an enzyme does not necessarily have a similar structure to the actual substrate. That would only be the case for a molecule that binds to the enzyme's active site. Moreover, the molecule binding to the allosteric site will almost always cause a conformational change in the enzyme's structure, but it can either enhance or inhibit the catalytic activity by doing so.
Example Question #56 : Enzyme Kinetics And Inhibition
Which of the following is true of zero-order reactions?
Substrate concentration is below Km
Velocity is inversely proportional to substrate
All of these
Velocity is direction proportional to the substrate
Velocity is independent of substrate
Velocity is independent of substrate
Zero order reactions are reactions in which the enzyme is saturated with substrate (in first order, the substrate concentration is below Km). The velocity in a zero-order reaction is independent of substrate concentration, therefore the two variables are not related. In a first order reaction, velocity is proportional to substrate concentration.
Example Question #57 : Enzyme Kinetics And Inhibition
Which of the following is not a property of enzymes?
No permanent changes in enzymes occur during the reactions they catalyze
All of these statements are true concerning enzymes
Enzymes do not change the concentrations of substrates and products at equilibrium
Enzymes are highly specific for substrates
Acceleration of reactions results from enzyme's ability to decrease activation energy
All of these statements are true concerning enzymes
All of the above statements are true concerning enzymes. They work to lower the activation energy of reactions and do not change the concentrations of substrates or products. They are highly specific and do not get changed by the reaction they are catalyzing.
Example Question #1 : Michaelis Menten Equation
For a given enzyme catalyzed reaction, the Michaelis constant is 0.6mM and the substrate concentration is 1.0mM. What is the fractional saturation of the enzyme under these conditions?
The fractional saturation of an enzyme is defined as the amount of enzyme that is bound to substrate divided by the total amount of enzyme. To calculate the fractional saturation, we'll need to use the Michaelis-Menton equation:
In addition, we'll need to define the rate and maximum rate in terms of enzyme concentrations:
From the above equations, we can calculate the fractional saturation of the enzyme:
Example Question #1 : Michaelis Menten Equation
Which of the following is true about the Michaelis constant for any given enzyme?
It is independent of the type of substrate
It is equal to
It increases as the enzyme’s specificity for the substrate decreases
It increases as the enzyme’s affinity for the substrate decreases
None of the other answers are true
It increases as the enzyme’s affinity for the substrate decreases
The Michaelis constant, , is not equal to , but is rather the substrate concentration when the reaction rate is . is an inverse measure of a substrate’s affinity for the enzyme. So as the affinity decreases, increases. Enzyme specificity is measured by a different constant, , the specificity constant. Although and specificity are in an inversely proportional relationship, does not necessarily increase as specificity decreases; rather, , also known as the catalytic constant, could decrease proportionally for a given enzyme. The Michaelis constant, being a measure of affinity, is going to differ for different types of substrates, depending on their shape and other features that influence their ability to bind to an enzyme.
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