Question 1

What is an allosteric enzyme?

Accepted Answer

An allosteric enzyme is an enzyme whose activity is regulated by the binding of a small effector molecule. This binding changes the shape of the enzyme, resulting in either an increase or decrease in its catalytic activity. Allosteric enzymes are important in regulating metabolic pathways within a cell.

Question 2

Which of the following describes how an enzyme can affect the transition state in an enzyme-catalyzed reaction?

Accepted Answer

Enzymes can affect the transition state by modifying the local pH, placing stress on bonds in the substrate, and bringing reactants together in the correct orientation, all of which lower the activation energy required for the reaction to proceed.

Question 3

Which of the following is a medical use of enzymes?

Accepted Answer

All of the choices are correct. Enzymes have various medical uses such as enzyme assays to diagnose damage or disease, injection of enzymes to counteract blood clots, enzyme replacement therapy for missing or malfunctioning enzymes, and being used as analytical reagents in the clinic laboratory.

Question 4

Elastase is a protease enzyme that cleaves peptide bonds on the carbonyl side of the amino acids glycine and alanine.What products result from treatment of a peptide with the primary structure shown below with elastase? Pro-Gly-Phe-Ala

Accepted Answer

Elastase cleaves peptide bonds on the carbonyl side of glycine and alanine, so it would cleave the peptide Pro-Gly-Phe-Ala between Gly-Phe and Phe-Ala, resulting in two peptides: Pro-Gly and Phe-Ala.

Question 5

Sucrase is an example of an enzyme that displays absolute specificity.What does the term "absolute specificity" indicate about an enzyme?

Accepted Answer

Absolute specificity means that an enzyme catalyzes the reaction of only a single substrate. In the case of sucrase, it specifically catalyzes the hydrolysis of sucrose into glucose and fructose, and does not react with any other substrates.

Question 6

About half of the 223 amino acids in the enzyme trypsin are hydrophobic. Where in the tertiary structure of this globular protein are these amino acids most likely to be found?

Accepted Answer

Hydrophobic amino acids tend to be found in the interior of globular proteins, away from water molecules. Therefore, they are most likely to be found in the interior of the folded protein.

Question 7

What term describes the pH at which an individual enzyme functions best?

Accepted Answer

The pH at which an enzyme functions best is referred to as the pH optimum.

Question 8

Which of the following best describes the type of binding between an irreversible inhibitor and an enzyme?

Accepted Answer

An irreversible inhibitor forms a very tight bond with the enzyme, permanently inactivating it. This is often due to covalent bonding between the inhibitor and a specific amino acid residue on the enzyme's active site. Weak, non-covalent, hydrogen bonding, or hydrophobic interactions are characteristic of reversible inhibition.

Question 9

The diagram below shows the energy pathway of an uncatalyzed reaction.How does the energy diagram change when an enzyme is used in the same reaction?

Accepted Answer

The answer of The diagram below shows the energy pathway...

Question 10

Lactase is an enzyme that catalyzes the following reaction.Which statement describing this reaction is FALSE?

Accepted Answer

The answer of Lactase is an enzyme that catalyzes the...

Question 11

Trypsin is a protease enzyme that cleaves peptide bonds on the carbonyl side of basic amino acids.Which labeled bond(s) in the peptide below would be cleaved by trypsin?

Accepted Answer

The answer of Trypsin is a protease enzyme that cleaves...

Question 12

Acetylcholine is a neurotransmitter that transmits a signal from a nerve cell to a muscle cell, causing the muscle to contract.How is the neurotransmitter inactivated so that the muscle can relax?

Accepted Answer

Acetylcholinesterase breaks down acetylcholine into acetic acid and choline, which are then reabsorbed by the neuron and used to create new molecules of acetylcholine. This process allows for the muscle to relax after contraction, as the neurotransmitter is no longer present to signal the muscle to contract.

Question 13

Proteases, or proteolytic enzymes, are responsible for which of the following functions?

Accepted Answer

Proteases, or proteolytic enzymes, are responsible for the hydrolysis of peptide bonds between amino acids in proteins.

Question 14

In feedback inhibition of an enzyme-catalyzed biosynthetic pathway, what frequently serves as the negative allosteric effector?

Accepted Answer

The final product of the pathway typically serves as the negative allosteric effector in feedback inhibition of an enzyme-catalyzed biosynthetic pathway. This helps to regulate the production of the final product and prevent excess accumulation.

Question 15

Which of the following correctly describes pepsinogen?

Accepted Answer

Pepsinogen is the inactive form of pepsin, which is activated by the acidic environment of the stomach. Once activated, pepsin catalyzes the hydrolysis of proteins into smaller peptides. Co-factors are substances that are required for enzyme activity, but pepsinogen does not act as a co-factor for pepsin. Pepsinogen is not an inhibitor of pepsin, but rather a precursor to the active enzyme. While pepsin and pepsinogen are related enzymes, pepsinogen is not an isoenzyme of pepsin. Finally, pepsin is not the name of the reaction catalyzed by pepsinogen, as pepsinogen is not an active enzyme.

Question 16

The pancreatic enzymes trypsin, chymotrypsin, and elastase all hydrolyze peptide bonds on the carbonyl side of several different amino acids in a protein.What term best describes their enzyme specificity?

Accepted Answer

These enzymes are described as having linkage specificity because they specifically target peptide bonds, which are a type of chemical bond.

Question 17

Proteolytic digestive enzymes are often produced in an inactive form.What is the name that refers to the inactive form of an enzyme?

Accepted Answer

The inactive form of an enzyme is called a proenzyme, also known as a zymogen. Proenzymes are activated through cleavage of specific peptide bonds within the protein.

Question 18

What three structurally similar pancreatic serine proteases function to cleave certain peptide bonds in proteins?

Accepted Answer

Trypsin, chymotrypsin, and elastase are three structurally similar pancreatic serine proteases that function to cleave certain peptide bonds in proteins. Pepsinogen is the precursor of pepsin, which is not structurally similar to the other pancreatic serine proteases, and acetylcholinesterase is not a pancreatic serine protease. Tryptophan is an amino acid, not a pancreatic serine protease, and choline and proline are not structurally similar pancreatic serine proteases that function in protein cleavage.

Question 19

The rate of an enzyme-catalyzed reaction initially increases with an increase in the substrate concentration, but eventually reaches a maximum value, even though the concentration of substrate continues to increase.Which of the following best explains why?

Accepted Answer

As substrate concentration increases, all the active sites of the enzyme become occupied with substrate molecules and no additional binding can occur. This is known as the saturation point of the enzyme-catalyzed reaction, beyond which the rate remains constant, as there are no more active sites available to bind with the excess substrate.

Question 20

The protease enzyme chymotrypsin cleaves peptide bonds on the carbonyl side of aromatic amino acids.Which labeled bond in the peptide below would be cleaved by chymotrypsin?

Accepted Answer

The answer of The protease enzyme chymotrypsin cleaves peptide bonds...

Quiz 19: Enzymes