Question 1

High concentrations of substrate overcome reversible inhibition by a transition-state analog because

Accepted Answer

The transition-state analog is a competitive inhibitor, meaning it competes with the substrate for binding at the active site. High concentrations of substrate can outcompete the inhibitor for binding, overcoming the inhibition.

Question 2

During the course of a transaminase reaction the enzyme exists in two states; one containing bound pyridoxal phosphate and the other containing bound pyridoxamine phosphate. Kinetically a transaminase reaction

Accepted Answer

A transaminase reaction is an example of an enzyme displaying ping-pong kinetics, where the enzyme and substrate undergo a series of reactions and form products in a stepwise fashion. In this case, the enzyme exists in two states, one containing pyridoxal phosphate and the other containing pyridoxamine phosphate. This leads to the ping-pong mechanism, where the amino group of the amino acid substrate is transferred to the keto group of the coenzyme, forming pyridoxamine phosphate, which then transfers the amino group to the ketone acceptor, forming the amino acid product and pyridoxal phosphate.

Question 3

A dehydrogenase would be placed in which enzyme category?

Accepted Answer

A dehydrogenase is an enzyme that catalyzes the removal of hydrogen atoms from a substrate. This is a type of oxidation-reduction reaction, which places the dehydrogenase under the category of oxidoreductases.

Question 4

Km is:

Accepted Answer

Km is related to the affinity of the enzyme for its substrate, meaning it reflects the concentration of substrate at which the enzyme is working at half of its maximal velocity (Vmax). It is not a measure of an inhibitor's concentration, the rate of product formation, the activation energy of the reaction, or a specific velocity.

Question 5

Where on the diagram above would the plot of a K class allosteric inhibitor coincide with the plot of a competitive inhibitor?

Accepted Answer

The answer of Where on the diagram above would the...

Question 6

Magnesium functions intracellularly as

Accepted Answer

Magnesium plays a vital role as an activator for over 300 enzymes involved in various cellular processes such as DNA and protein synthesis, energy metabolism, and muscle and nerve function.

Question 7

Allosteric control most often occurs through changes in Allosteric control most often occurs through changes in

Accepted Answer

Allosteric control typically involves changes in Km, which reflects the enzyme's affinity for its substrate, rather than changes in Vmax or substrate concentrations.

Question 8

For an enzyme reaction that requires a coenzyme

Accepted Answer

Coenzymes are organic molecules that work with enzymes to facilitate the enzyme's catalytic activities. They often participate in the reaction and react with the substrate, such as the role of NAD+ in the oxidation of glucose.

Question 9

Each of the following statements about the Michaelis-Menten equation is correct EXCEPT which one?

Accepted Answer

For a group-specific enzyme, the substrate with the largest Km is actually the one with the weakest binding to the active site. This is because a larger Km value indicates a lower affinity of the enzyme for that particular substrate.

Question 10

In general, when the enzyme concentration is doubled the rate of an enzyme catalyzed reaction is

Accepted Answer

Enzyme concentration is directly proportional to the rate of an enzyme-catalyzed reaction. Therefore, doubling the enzyme concentration doubles the rate of the reaction.

Question 11

What is the reaction rate in a simple enzymatic system, if the substrate concentration is much less than Km?

Accepted Answer

When the substrate concentration is much less than Km, the reaction rate is virtually proportional to the substrate concentration. This is because, under these conditions, the enzyme-substrate complex formation is limited by the availability of substrate, making the reaction rate depend directly on how much substrate is present.

Question 12

Creatine kinase (CK) activity is used as an early indicator and the LDH activity is used as an delayed indicator of myocardial infarction. This difference in time of appearance in serum is influenced by

Accepted Answer

Molecular mass, half-life of the enzyme in blood, and association of the enzyme with cellular components can all influence the time of appearance of an enzyme in serum. Therefore, the correct choice is D, "all of the above".

Question 13

The International Unit (I.U.) for enzyme activity is that amount of enzyme which at 30⁰ C will convert substrate to product at a rate of

Accepted Answer

The definition of the International Unit implies that it refers to the enzyme activity at a specific temperature (30°C) and the rate of conversion of the substrate to the product is given in micromoles per minute. Therefore, the correct choice would be option A) 1 micromole/min.

Question 14

A competitive inhibitor

Accepted Answer

A competitive inhibitor competes with the substrate for binding to the active site of the enzyme. This increases the apparent Km of the enzyme for its substrate, as more substrate is needed to achieve a given reaction rate in the presence of the inhibitor. The maximum velocity (Vmax) of the reaction remains the same, as the inhibitor does not affect the enzyme's catalytic activity.

Question 15

In the presence of an irreversible inhibitor

Accepted Answer

In the presence of an irreversible inhibitor, the inhibitor binds covalently to the enzyme, resulting in a permanent loss of activity. This means that the number of functional enzyme molecules decreases, which leads to a decrease in Vmax. The binding of the inhibitor also alters the active site of the enzyme, which can increase the apparent Km value for its substrate. Therefore, there is a decrease in Vmax and possibly an increase in Km, which corresponds to choice D.

Question 16

The intercept on the vertical axis (Y-axis) on a Lineweaver-Burk plot is equal to

Accepted Answer

The intercept on the vertical axis (Y-axis) of a Lineweaver-Burk plot represents 1/Vmax. This plot is a double reciprocal graph of the Michaelis-Menten equation, used to determine enzyme kinetics.

Question 17

Which of the following is LEAST likely to affect the Vmax of an enzyme?

Accepted Answer

Vmax, the maximum rate of an enzyme-catalyzed reaction when the enzyme is saturated with substrate, is not affected by competitive inhibitors. Competitive inhibitors increase the Km (the substrate concentration at which the reaction rate is half of Vmax) because they compete with the substrate for binding to the active site, but they do not affect the Vmax since the inhibition can be overcome by increasing substrate concentration.

Question 18

For any enzymatic reaction, when the ratio of enzyme substrate complex to free enzyme [ES]/[E] increases.

Accepted Answer

An increase in the ratio of [ES]/[E] signifies that more enzyme-substrate complexes are being formed, indicating that the reaction is proceeding at a faster rate. Therefore, the velocity of the reaction will increase.

Question 19

Hydrolysis of high energy phosphate bonds associated with enzymatic linking of two molecules is catalyzed by what group of enzymes?

Accepted Answer

Ligases catalyze the joining of two molecules with the concomitant hydrolysis of a high-energy phosphate bond, often using energy derived from ATP.

Question 20

A Schiff base is formed by the interaction between

Accepted Answer

A Schiff base is formed by the interaction between an amine and an aldehyde. This reaction involves a nucleophilic addition of the amine to the carbonyl group of the aldehyde, followed by dehydration to form the Schiff base.

Quiz 10: Enzymes: Classification, Kinetics, and Control