Medicinal Chemistry Chapter 03 Key

Type: multiple choice Title: Chapter 03 - Question 01 01) Which of the following statements is not true regarding the active site of an enzyme? Feedback: An active site is normally a hollow or cleft on the surface of an enzyme, rather than the surface itself. Correct a.# An active site is normally on the surface of an enzyme. incorrect b.# An active site is normally hydrophobic in nature. incorrect c.# incorrect d.# Substrates fit into active sites and bind to functional groups within the active site. An active site contains amino acids which are important to the binding process and the catalytic mechanism. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 02 02) Some enzymes have a binding site which is not recognised by the normal substrate, and affects the activity of the enzyme if it is occupied by a ligand. What term is used for such a binding site? Feedback: The allosteric binding site affects the activity of an enzyme, depending on whether it is occupied by a ligand or not. It is distinct from the active site where the enzyme catalysed reaction takes place. The terms secondary binding site and inhibitory binding site do not exist. incorrect a.# Active site. Correct b.# Allosteric binding site. incorrect c.# Secondary binding site. incorrect d.# Inhibitory binding site. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 03 03) What term is used to describe the binding site of an enzyme where a reaction is catalysed? Feedback: The active site is where the reaction catalysed by the enzyme takes place. The allosteric binding site affects the activity of an enzyme, depending on whether it is occupied by a ligand or not. It is distinct from the active site. The terms secondary binding site and inhibitory binding site do not exist. Correct a.# Active site. incorrect b.# Allosteric binding site. incorrect c.# Secondary binding site. incorrect d.# Inhibitory binding site. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 04 04) Which of the following terms refers to the process by which a substrate binds to an active site and alters the shape of that active site? Feedback: An induced fit is a consequence of the binding interactions taking place between a substrate and the active site. The term moulded fit does not exist. The lock and key theory is an older theory where it was proposed that the active site was already the correct shape for its substrate. incorrect a.# Moulded fit. incorrect b.# Intermolecular bonding. Correct c.# Induced fit. incorrect d.# Lock and key theory. END OF QUESTION Type: matching Title: Chapter 03 - Question 05 05) Identify which of the amino acids; glutamate, phenylalanine, threonine, and serine, would use the following interactions in an active site; hydrogen bonding, ionic bonding, van der Waals interactions, H-bonding, and van der Waals interactions. Feedback: Serine has a hydroxyl group which can take part in hydrogen bonding. Glutamate is the ionised form of glutamic acid and can take part in ionic interactions. Phenylalanine has an aromatic ring in its side chain that can interact by van der Waals interactions. Tyrosine has an aromatic ring that can interact by van der Waals interactions, and a phenol that can interact by hydrogen bonding. a.# Hydrogen bonding = Serine b.# Ionic bonding = Glutamate c.# Van der Waals interactions = Phenylalanine Hydrogen bonding and van der Waals bonding END OF QUESTION = Tyrosine d.# Type: multiple choice Title: Chapter 03 - Question 06 06) Which of the following descriptions best describes a cofactor? Feedback: A cofactor is a non-protein substance required by an enzyme to function properly. This term covers both organic molecules and metal ions. A co-enzyme is a non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. A prosthetic group is a non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. A substrate is a compound which is bound to the active site and undergoes a reaction. Correct a.# A non-protein substance that is required by an enzyme if it is to catalyse a reaction. incorrect b.# A non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. incorrect c.# A non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. incorrect d.# A compound which is bound to the active site and undergoes a reaction. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 07 07) Which of the following descriptions best describes a coenzyme? Feedback: A cofactor is a non-protein substance required by an enzyme to function properly. This term covers both organic molecules and metal ions. A co-enzyme is a non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. A prosthetic group is a non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. A substrate is a compound which is bound to the active site and undergoes a reaction. incorrect a.# A non-protein substance that is required by an enzyme if it is to catalyse a reaction. Correct b.# A non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. incorrect c.# A non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. incorrect d.# A compound which is bound to the active site and undergoes a reaction. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 08 08) Which of the following descriptions best describes a prosthetic group? Feedback: A cofactor is a non-protein substance required by an enzyme to function properly. This term covers both organic molecules and metal ions. A co-enzyme is a non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. A prosthetic group is a non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. A substrate is a compound which is bound to the active site and undergoes a reaction. incorrect a.# A non-protein substance that is required by an enzyme if it is to catalyse a reaction. incorrect b.# A non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. Correct c.# A non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. incorrect d.# A compound which is bound to the active site and undergoes a reaction. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 09 09) Which of the following descriptions best describes a substrate? Feedback: A cofactor is a non-protein substance required by an enzyme to function properly. This term covers both organic molecules and metal ions. A co-enzyme is a non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. A prosthetic group is a non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. A substrate is a compound which is bound to the active site and undergoes a reaction. incorrect a.# A non-protein substance that is required by an enzyme if it is to catalyse a reaction. incorrect b.# A non-protein organic molecule that is required by some enzymes in order to catalyse a reaction on a substrate. incorrect c.# Correct d.# A non-protein organic molecule that is bound covalently to the active site of an enzyme, and which is required if the enzyme is to catalyse a reaction on a substrate. A compound which is bound to the active site and undergoes a reaction. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 10 10) Consider the following enzyme-catalysed reaction carried out on glycogen. What is the product? Feedback: Glycogen is the substrate for this reaction. Adrenaline is a hormone that can trigger a cascade of cellular events that will eventually activate phosphorylase a. AMP acts as an enzyme modulator to directly activate the enzyme. Glucose is the structure formed if the phosphate group is hydrolysed from glucose-1-phosphate. Correct a.# Glucose-1-phosphate. incorrect b.# Adrenaline. incorrect c.# Glucose. incorrect d.# AMP. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 11 11) Consider the following enzyme catalysed reaction. What is the substrate? Feedback: Glycogen is the substrate for this reaction. Phosphorylase a is the enzyme. AMP acts as an enzyme modulator to directly activate the enzyme. Glucose-1-phosphate is the product. incorrect a.# Glucose-1-phosphate. incorrect b.# Phosphorylase a. Correct c.# Glycogen. incorrect d.# AMP. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 12 12) Consider the following enzyme-catalysed reaction. What is the enzyme? Feedback: Glycogen is the substrate for this reaction. Phosphorylase a is the enzyme. AMP acts as an enzyme modulator to directly activate the enzyme. Glucose-1-phosphate is the product. incorrect a.# Glucose-1-phosphate. Correct b.# Phosphorylase a. incorrect c.# Glycogen. incorrect d.# AMP. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 13 13) Consider the following enzyme-catalysed reaction. What is the enzyme modulator that activates the enzyme? Feedback: Glycogen is the substrate for this reaction. Phosphorylase a is the enzyme. AMP acts as an enzyme modulator to directly activate the enzyme. Glucose-1-phosphate is the product. incorrect a.# Glucose-1-phosphate. incorrect b.# Phosphorylase a. incorrect c.# Glycogen. Correct d.# AMP. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 14 14) Consider the following enzyme-catalysed reaction. What sort of enzyme is involved? Feedback: The reaction shown is a phosphorylation and so the enzyme involved is a phosphorylase. Esterases catalyse the hydrolysis of esters. Ligases catalyse the joining of two substrates. Transferases catalyse group transfer reactions. incorrect a.# Esterase. Correct b.# Phosphorylase . incorrect c.# Ligase. incorrect d.# Transferas. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 15 15) Consider the following enzyme-catalysed reaction. What chemical messenger triggers a cascade of cellular event that eventually activates the enzyme involved in this reaction? Feedback: Adrenaline is a hormone that can trigger the signalling cascade. The other agents mentioned are neurotransmitters which do not have an affect on this reaction. incorrect a.# Acetylcholine. incorrect b.# Noradrenaline. incorrect c.# Serotonin. Correct d.# Adrenaline. END OF QUESTION Type: matching Title: Chapter 03 - Question 16 16) Identify A-D in the following reaction. Feedback: Nitrous oxide activates cyclase enzymes to generate the secondary messenger cyclic GMP from GTP. a.# A = Guanosine triphosphate b.# B = Nitric oxide c.# C = Cyclase d.# D = Cyclic GMP END OF QUESTION Type: matching Title: Chapter 03 - Question 17 17) Identify A-D in the following diagram. Feedback: Arginine contains a guanidine functional group that provides the nitrous oxide that is eventually formed in this reaction. The enzyme NO synthase converts arginine to citrulline in two steps with release of nitrous oxide. a.# A = Arginine b.# B = NO synthase c.# C = Citrulline d.# D = Nitric oxide END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 18 18) Which of the following statements is not true regarding the active site of an enzyme? Feedback: An active site is normally hydrophobic in nature, not hydrophilic. Nevertheless, there are usually hydrophilic amino acids present which are important in binding the substrate in the active site. incorrect a.# An active site is normally a hollow or cleft on the surface of an enzyme. Correct b.# An active site is normally hydrophilic in nature. incorrect c.# incorrect d.# Substrates fit into active sites and bind to functional groups within the active site. An active site contains amino acids which are important to the binding process and the catalytic mechanism. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 19 19) Which of the following amino acids commonly acts as a nucleophilic group in enzyme-catalysed reaction mechanisms? Feedback: Serine has a hydroxyl functional group that is frequently involved as a nucleophile in enzyme catalysed reactions. Cysteine is another amino acid that is commonly present as a nucleophile in enzyme active sites. Phenylalanine and valine are more likely to be involved in binding interactions. Histidine is commonly present as an acid-base catalyst. Correct a.# Serine. incorrect b.# Phenylalanine. incorrect c.# Histidine. incorrect d.# Valine. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 20 20) Which of the following amino acids acts as a nucleophilic group in enzyme-catalysed reaction mechanisms? Feedback: Cysteine has a thiol functional group that is frequently involved as a nucleophile in enzyme catalysed reactions. Serine is another amino acid that is commonly present as a nucleophile in enzyme active sites. Threonine, tyrosine and glutamine are more likely to be involved in binding interactions. incorrect a.# Threonine. incorrect b.# Tyrosine. Correct c.# Cysteine. incorrect d.# Glutamine. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 21 21) Which of the following amino acids acts as an acid-base catalyst in enzyme-catalysed reaction mechanisms? Feedback: Histidine is a weak base that can equilibrate between a protonated, ionised form and a non-protonated free base. It is, therefore, well placed to act as an acid-base catalyst. Phenylalanine, serine, and tryptophan can all be involved in substrate binding, while serine may act as a nucleophile. incorrect a.# Serine. incorrect b.# Phenylalanine. Correct c.# Histidine. incorrect d.# Tryptophan. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 22 22) From which amino acid is nitrous oxide generated? Feedback: Arginine contains a guanidine functional group that provides the nitrous oxide. The enzyme NO synthase converts arginine to citrulline with release of nitrous oxide. Correct a.# Arginine. incorrect b.# Aspartic acid. incorrect c.# Asparagine. incorrect d.# Lysine. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 23 23) What term is used for enzymes such as COX-1 and COX-2 which vary in structure and location but which catalyse the same reaction? Feedback: Isozymes is the correct term. Isosteres are chemical moieties that have similar size, shape, and valency. Isotopes are elements having the same number of protons, but a different number of neutrons. Isomers are molecules with the same molecular formula but differ in the way the atoms and bonds are linked together or are orientated with respect to each other. incorrect a.# Isosteres. Correct b.# Isozymes. incorrect c.# Isotopes. incorrect d.# Isomers. END OF QUESTION Type: multiple choice Title: Chapter 03 - Question 24 24) Which of the following statements is true with respect to the Michaelis constant? Feedback: The Michaelis constant is determined by measuring how the enzymecatalysed rate of reaction is affected by substrate concentration. Inhibitors are not involved and so options b) and c) are wrong. The Michaelis constant is the concentration of substrate at which the rate of reaction is half of its maximum value. Correct a.# It is equal to the concentration of substrate at which the reaction rate is half of its maximum value. incorrect b.# It is equal to the concentration of inhibitor at which the reaction rate is half of its maximum value. incorrect c.# It is equal to the concentration of substrate at which the reaction rate is at its maximum value. incorrect d.# END OF QUESTION It is equal to the concentration of inhibitor at which the reaction rate is zero.