Medicinal Chemistry Chapter 04 Key

Type: multiple choice Title: Chapter 04 - Question 01 01) Which of the following statements is not true about receptors? Feedback: Some protein receptors are certainly present inside cells, but the majority are present in the cell membrane. The binding site of receptors is analogous to the active site of enzymes. However, no reaction is catalysed. The ligand for the binding site acts as a chemical messenger. It binds and causes an induced fit that result in 'knock on effects' which lead to a message being received in the cell. Receptors do not catalyse reactions and so a messenger departs unchanged. Correct a.# Most receptors are proteins situated inside the cell. incorrect b.# incorrect c.# incorrect d.# Receptors contain a hollow or cleft on their surface which is known as a binding site. Receptors bind chemical messengers such as neurotransmitters or hormones. Receptors do not catalyse reactions on chemical messengers. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 02 02) Which of the following statements is not true? Feedback: The receptors for neurotransmitters are located in the cell membranes of target cells and not within the cell itself. incorrect a.# Neurotransmitters are released by nerves. incorrect b.# incorrect c.# Correct d.# Neurotransmitters are required to carry a 'message' from a nerve to a target cell. Neurotransmitters only have small distances to cover to reach their target cells. Neurotransmitters bind to receptors within target cells. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 03 03) Which of the following is not a neurotransmitter? Feedback: Cyclic GMP is a secondary messenger that is formed 'downstream' of a receptor-activated process. incorrect a.# Glycine. Correct b.# Cyclic GMP. incorrect c.# -Aminobutyric acid. incorrect d.# Serotonin. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 04 04) Which of the following statements is not true regarding the binding site of a receptor? Feedback: The binding site is a hollow or cleft in the surface of the protein and is usually hydrophobic in character. incorrect a.# The binding site is normally a hollow or cleft in the surface of an receptor. Correct b.# The binding site is normally hydrophilic in nature. incorrect c.# incorrect d.# Chemical messengers fit into binding sites and bind to functional groups within the binding site. The binding site contains amino acids which are important to the binding process. END OF QUESTION Type: matching Title: Chapter 04 - Question 05 05) Which of the following amino acid residues is likely to form its strongest binding interaction by means of: Feedback: Valine has an alkyl side chain capable of forming van der Waals interactions. Glycine has no side chain or residue and so cannot form any interactions. Serine has an alcohol functional group capable of hydrogen bonding. Aspartate has an ionised carboxylate group which is capable of ionic bonding. It is also possible for this group to interact by hydrogen bonding as a hydrogen bond acceptor, but this will be weaker than an ionic bond. a.# Hydrogen bonding = Serine b.# Ionic bonding = Aspartate c.# Van der Waals interactions = Valine d.# None of these options = Glycine END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 06 06) Which of the following statements best describes an induced fit? Feedback: An induced fit refers to the way the binding site changes shape as a result of the binding interactions formed between it and the chemical messenger. An induced fit cannot take place before the chemical messenger binds. The chemical messenger must be in the correct conformation to bind effectively, but this is a process which is not controlled by the binding site. The likelihood of a molecule being in the active conformation will depend on how stable the active conformation is relative to other inactive conformations. incorrect a.# The process by which a binding site alters shape such that it is ready to accept a chemical messenger. incorrect b.# The process by which a chemical messenger adopts the correct binding conformation before entering a binding site. Correct c.# The process by which binding of a chemical messenger to a binding site alters the shape of the binding site. incorrect d.# The process by which a binding site alters the shape of the chemical messenger into the binding conformation before binding. END OF QUESTION Type: matching Title: Chapter 04 - Question 07 07) Which of the following amino acid residues is likely to form its strongest binding interaction by means of: Feedback: Alanine has an alkyl side chain capable of forming van der Waals interactions. Glycine has no side chain or residue. Threonine has an alcohol functional group capable of hydrogen bonding. Lysine has an amino group which could be protonated to form an ionised centre capable of ionic bonding. It is also possible for this group to interact by hydrogen bonding, either in the ionised or non-ionised forms, but this will be weaker than an ionic bond. a.# Hydrogen bonding = Threonine b.# Ionic bonding = Lysine c.# Van der Waals interactions = Alanine d.# None of the answers = Glycine END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 08 08) There is a fine balance required for the binding interactions of a neurotransmitter with its receptor. Which of the following statements best expands on this statement? Feedback: All the statements are accurate, but the following statement best describes the importance of having an equilibrium between the bound and unbound states of the chemical messenger: ‘The binding interactions must be sufficiently strong that the neurotransmitter binds long enough to have an effect, but not too strong in case the neurotransmitter remains permanently bound.’ If the interaction was too weak, the messenger would not be bound long enough to have an effect. If too strong, the receptor would be continually activated. incorrect a.# It is important that the binding interactions involve a mixture of van der Waals interactions, hydrogen bonds and ionic bonds since neurotransmitters have different functional groups. incorrect b.# The binding interactions must be of the correct nature to match the functional groups of the neurotransmitter and the functional groups in the binding site. Correct c.# The binding interactions must be sufficiently strong that the neurotransmitter binds long enough to have an effect, but not too strong in case the neurotransmitter remains permanently bound. incorrect d.# There must be the correct balance of hydrophilic and hydrophobic interactions to ensure that the chemical messenger can enter a hydrophobic binding site. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 09 09) When a membrane-bound receptor binds its chemical messenger, an induced fit takes place which leads to secondary effects, allowing a chemical message to be received within the cell. Which of the following mechanisms is not involved in this process? Feedback: Transport proteins are involved in transporting molecules across cell membranes, and are not receptors. If a receptor is present in the cell membrane, there is no need for a chemical messenger to enter the cell. If the receptor is within the cell, the chemical messengers are generally hydrophobic and can pass through the cell membrane on their own account. Correct a.# The transport of the chemical messenger into the cell. incorrect b.# The opening or closing of an ion channel. incorrect c.# The activation of a signal protein. incorrect d.# The activation of a membrane-bound enzyme. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 10 10) Which of the following statements is not true about a ligand-gated ion channel receptor? Feedback: Ligand-gated ion channels consist of five glycoproteins and not six. The other statements are correct. Receptors that are controlled by the membrane potential are known as voltage-gated ion channels. incorrect a.# incorrect b.# Correct c.# incorrect d.# Ligand-gated ion channel receptors are present in the cell membrane. Neurotransmitters can act as the chemical messengers for ligand-gated ion channels. Ligand-gated ion channels consist of six glycoproteins. Some ion channel receptors are controlled by differences in membrane potential rather than by ligands. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 11 11) Which of the following statements is not true about ligand-gated ion channels? Feedback: The response time of ligand-gated ion channels to neurotransmitters is fast rather than slow. The other statements are correct. incorrect a.# There are different ligand-gated ion channels for specific ions. Correct b.# The response time to a neurotransmitter is slow. incorrect c.# incorrect d.# The process by which an ion channel opens as a result of receptor-ligand binding is known as gating. The opening of cationic ion channels generally leads to depolarisation of the cell. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 12 12) Which of the following statements is true about the ion channel controlled by the nicotinic receptor? Feedback: Three of the options are wrong for the following reasons: Each protein subunit of the ion channel contains four hydrophobic regions which traverse the cell membrane Two of the protein subunits are identical (the -subunits) The binding site for the nicotinic receptor is shared between the -protein subunit and a neighbouring protein subunit. There are two binding sites per ion channel. Therefore the following option is correct: ‘Each protein subunit of the ion channel has a lengthy N-terminal extracellular chain.’ incorrect a.# Each protein subunit of the ion channel contains three hydrophobic regions which traverse the cell membrane. incorrect b.# Three of the protein subunits are identical (the -subunits). incorrect c.# Correct d.# END OF QUESTION Type: multiple choice The binding site for the nicotinic receptor is located solely on the -subunit which means that there are two binding sites per ion channel. Each protein subunit of the ion channel has a lengthy Nterminal extracellular chain. Title: Chapter 04 - Question 13 13) The nicotinic receptor controls an ion channel. Which of the following statements is true about the -subunit of this ion channel? Feedback: The N-terminal and C-terminal chains are both extracellular. There are two intracellular loops and only one extracellular loop. incorrect a.# The N-terminal and C-terminal chains are both intracellular. incorrect b.# There is one intracellular loop. Correct c.# incorrect d.# The binding site for the neurotransmitter resides solely on the N-terminal chain. There are two extracellular loops END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 14 The mechanism of gating involves the rotation of five kinked -helices which traverse the cell membrane. Which of the following statements is untrue? Feedback: It is the -helix of the second transmembrane section that is involved and not the first. The other statements are correct. incorrect a.# Each protein subunit making up the ion channel contributes one of the kinked -helices. Correct b.# It is the -helix of the first transmembrane section that is involved. incorrect c.# Rotation of the helices opens up a central channel to allow the flow of ions. incorrect d.# The neurotransmitter binds to the N-terminal chain to produce a rapid response. END OF QUESTION 14) Type: multiple choice Title: Chapter 04 - Question 15 15) Which of the following statements is true about a G-protein coupled receptor? Feedback: There are seven transmembrane hydrophobic regions. The number of intracellular and extracellular loops is the same. The N-terminal chain is extracellular and the C-terminal chain is intracellular. The binding region for the G-protein involves one of the intracellular loops and the C-terminal chain, as stated. incorrect a.# It contains five transmembrane hydrophobic sections. Incorrect b.# There are more extracellular loops than intracellular loops. Correct c.# Incorrect d.# The binding region for the G-protein involves one of the intracellular loops and the C-terminal chain. The N-terminal chain is intracellular and the C-terminal chain is extracellular. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 16 16) Which of the following is not a G-protein coupled receptor? Feedback: The nicotinic receptor is an ion channel. incorrect a.# The histamine receptor. Correct b.# The nicotinic receptor. incorrect c.# The dopaminergic receptor. incorrect d.# The adrenergic receptor. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 17 17) Which of the following statements is not true about G-protein coupled receptors? Feedback: Growth factors are ligands for kinase-linked receptors. incorrect a.# They contain seven transmembrane sections. incorrect b.# They mediate the action of some hormones. incorrect c.# They activate signal proteins called G-proteins. Correct d.# Growth factors can act as ligands for some G-protein coupled receptors. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 18 18) Which of the following pairs of receptors illustrates convergent evolution? Feedback: Both the H1 and H2 receptors bind histamine, but they have evolved from different branches of the evolutionary tree. The other pairings are examples of divergent evolution since they have evolved from the same branch. incorrect a.# The D1B and D1A dopaminergic receptor subtypes. Correct b.# The H1 and H2 receptor subtypes. incorrect c.# The 2a and 2b adrenoceptor subtypes. incorrect d.# The M2 and M4 muscarinic receptor subtypes. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 19 19) Which of the following statements is true about a tyrosine kinase linked receptor? Feedback: The receptor is situated in the cell membrane. The N-terminal chain is extracellular and this is where the ligand binding site is. The receptor has one hydrophobic transmembrane region as stated. incorrect a.# It is situated in the cytoplasm. incorrect b.# The N-terminal chain is intracellular. incorrect c.# The ligand binding site is in the C-terminal chain. Correct d.# It has one hydrophobic transmembrane region. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 20 20) Which of the following is a messenger for a tyrosine kinase linked receptor? Feedback: Adrenaline, dopamine, and histidine are neurotransmitters that activate G- protein coupled receptors. The epidermal growth factor activates a tyrosine kinase linked receptor. incorrect a.# Adrenaline. incorrect b.# Dopamine. Correct c.# Epidermal growth factor. incorrect d.# Histidine. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 21 21) Which of the following statements is untrue regarding the epidermal growth factor receptor? Feedback: Activation of the kinase results in the phosphorylation of tyrosine residues and not serine residues. It is a tyrosine kinase and not a serine-threonine kinase. incorrect a.# Binding of epidermal growth factor results in dimerisation of the receptor. incorrect b.# Dimerisation activates the kinase active site. Correct c.# incorrect d.# Activation of the kinase results in phosphorylation of serine residues. One half of the receptor dimer catalyses reactions on residues present on the other half. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 22 22) Which of the following statements is true regarding intracellular receptors? Feedback: Intracellular receptors are single proteins. They contain a ligand binding site near the C-terminal end. They contain a binding region for DNA near the middle of the protein and they are activated by hydrophobic molecules which are extracellular messengers and cross the cell membrane to reach their target. incorrect a.# They consist of three protein subunits. incorrect b.# They contain a ligand binding site near the N-terminal end. Correct c.# incorrect d.# They contain a binding region for DNA near the middle of the protein. They are activated by hydrophobic molecules which are synthesised within the cell. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 23 23) Which of the following statements is true regarding the DNA binding region of intracellular receptors? Feedback: The DNA binding region of intracellular receptors contains nine cysteine residues, eight of which are involved in binding two zinc ions. The receptor does not contain nucleotides. The DNA binding region is known as the zinc finger domains. Correct a.# It contains nine cysteine residues. incorrect b.# Four cysteine residues are involved in binding two zinc ions. incorrect c.# It contains particular nucleotide sequences that can base pair to DNA. incorrect d.# The DNA binding region is known as having 'thiol fingers'. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 24 24) Which of the following statements is not true about a ligand-gated ion channel receptor? Feedback: Ligand-gated ion channels are controlled by ligands and not by the membrane potential. Voltage-gated ion channels are controlled by membrane potential. incorrect a.# Ligand-gated ion channel receptors are present in the cell membrane. incorrect b.# Neurotransmitters can act as the chemical messengers for ligand-gated ion channels. incorrect c.# Ligand-gated ion channels consist of five glycoproteins. Correct d.# Differences in membrane potential affect whether ligand-gated ion channel receptors open or close. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 25 25) Which of the following statements is not true about ligand-gated ion channels? Feedback: The opening of cationic ion channels generally leads to depolarisation of the cell. incorrect a.# There are different ligand-gated ion channels for specific ions. incorrect b.# The response time to a neurotransmitter is extremely fast. incorrect c.# Correct d.# The process by which an ion channel opens as a result of receptor-ligand binding is known as gating. The opening of cationic ion channels generally leads to polarisation of the cell. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 26 26) Which of the following statements is true about the ion channel controlled by the nicotinic receptor? Feedback: There are four hydrophobic regions for each protein subunit. The binding site is shared between the -protein subunit and a neighbouring protein subunit. However, there are two binding sites per ion channel. The N-terminal chain is extracellular and not intracellular. incorrect a.# Each protein subunit of the ion channel contains three hydrophobic regions which traverse the cell membrane. Correct b.# Two of the protein subunits are identical (the -subunit). incorrect c.# incorrect d.# END OF QUESTION Type: multiple choice The binding site for the nicotinic receptor is located solely on the -subunit which means that there are two binding sites per ion channel. Each protein subunit of the ion channel has a lengthy Nterminal intracellular chain. Title: Chapter 04 - Question 27 27) The nicotinic receptor controls an ion channel. Which of the following statements is true about the -subunit of this ion channel? Feedback: There are two intracellular loops. The binding site for the neurotransmitter resides solely on the N-terminal chain. There is only one extracellular loop. Correct a.# The N-terminal and C-terminal chains are both extracellular. incorrect b.# There is one intracellular loop. incorrect c.# incorrect d.# The binding site for the neurotransmitter resides solely on the C-terminal chain. There are two extracellular loops. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 28 The mechanism of gating involves the rotation of five kinked -helices which traverse the cell membrane. Which of the following statements is untrue? Feedback: The neurotransmitter produces a rapid response but it binds to the Nterminal chain. incorrect a.# Each protein subunit making up the ion channel contributes one of the kinked -helices. incorrect b.# It is the -helix of the second transmembrane section that is involved. incorrect c.# Rotation of the helices opens up a central channel to allow the flow of ions. Correct d.# The neurotransmitter binds directly to the TM2 section to produce a rapid response. END OF QUESTION 28) Type: multiple choice Title: Chapter 04 - Question 29 29) How many transmembrane sections are there in a G-protein coupled receptor? Feedback: G-Protein coupled receptors are also known as 7-TM receptors, where TM stands for transmembrane. incorrect a.# 1 incorrect b.# 3 incorrect c.# 5 Correct d.# 7 END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 30 30) Which of the following statements is true about a G-protein coupled receptor? Feedback: The N-terminal chain is extracellular and the C-terminal chain is intracellular. However, there are seven transmembrane hydrophobic regions. There are the same number of intracellular and extracellular loops. The binding region of the G-protein involves one of the intracellular loops and the Cterminal chain. incorrect a.# It contains five transmembrane hydrophobic sections. incorrect b.# There are more extracellular loops than intracellular loops. incorrect c.# Correct d.# The binding region for the G-protein involves two extracellular loops. The N-terminal chain is extracellular and the C-terminal chain is intracellular. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 31 31) Which of the following is not a G-protein coupled receptor? Feedback: The glycine receptor is an ion channel. incorrect a.# The muscarinic receptor. Correct b.# The glycine receptor. incorrect c.# The adrenergic receptor. incorrect d.# The glutamate receptor. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 32 32) Which of the following statements is not true about G-protein coupled receptors? Feedback: Fast-acting neurotransmitters generally activate ion channels since the secondary effect is faster than that of G-protein coupled receptors. Correct a.# They generally mediate the action of fast acting neurotransmitters. incorrect b.# They mediate the action of some hormones. incorrect c.# They activate signal proteins called G-proteins. incorrect d.# Calcium ions can act as a ligand for some G-protein coupled receptors. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 33 33) Which of the following pairs of receptors are likely to show the greatest structural similarity? Feedback: These receptors are closely related on the evolutionary tree of G-protein coupled receptors. The other pairings are more distantly related. incorrect a.# The dopamine receptor subtypes D3 and D5. incorrect b.# The muscarinic receptor M2 and the -adrenergic receptor 2. Correct c.# The histamine H2 receptor and the 1 adrenoceptor. incorrect d.# The histamine H1 receptor and the 2 adrenergic receptor. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 34 34) Which of the following statements is true about a tyrosine kinase linked receptor? Feedback: The ligand binding site is in the N-terminal chain is a true statement. The receptor is situated in the cell membrane. The N-terminal chain is extracellular and this is where the ligand binding site is. There is only one hydrophobic transmembrane region. incorrect a.# It is situated in the cytoplasm. incorrect b.# The N-terminal chain is intracellular. Correct c.# The ligand binding site is in the N-terminal chain. incorrect d.# It has two hydrophobic transmembrane regions. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 35 35) Which of the following reactions is catalysed by a tyrosine kinase? Feedback: Esterifications are catalysed by esterases. A tyrosine kinase phosphorylates the phenol functional group present on the side chain of the amino acid tyrosine. incorrect a.# The phosphorylation of an alcohol functional group. incorrect b.# The esterification of an alcohol functional group. Correct c.# The phosphorylation of a phenol functional group. incorrect d.# The esterification of a phenol functional group. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 36 36) Which of the following terms describes the epidermal growth factor? Feedback: The epidermal growth factor is a bivalent ligand which can bind to two binding sites on different proteins allowing dimerisation and activation of the protein receptor. incorrect a.# Divalent ligand. incorrect b.# Heterovalent ligand. incorrect c.# Covalent ligand. Correct d.# Bivalent ligand. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 37 37) Which of the following statements is untrue regarding the epidermal growth factor receptor? Feedback: ATP and not GTP is required for phosphorylation. The other statements are accurate. incorrect a.# Binding of epidermal growth factor results in dimerisation of the receptor. incorrect b.# Dimerisation activates the tyrosine kinase active site. incorrect c.# Correct d.# END OF QUESTION Activation of tyrosine kinase results in phosphorylation of tyrosine residues on the other half of the dimer. GTP is required for phosphorylation. Type: multiple choice Title: Chapter 04 - Question 38 38) In what way does the insulin receptor differ from the EGF receptor? Feedback: The insulin receptor is preformed before the ligand binds whereas the EGF receptor requires the presence of its ligand to dimerise. All the other statements are true for both kinds of receptor. Correct a.# The receptor is preformed prior to ligand binding. incorrect b.# A tyrosine kinase active site is activated. incorrect c.# incorrect d.# Phosphorylation of one half of the receptor complex is catalysed by enzyme active sites on the other half. ATP is required for phosphorylation. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 39 39) In what way does the growth hormone receptor differ from the EGF receptor? Feedback: The growth hormone receptor is formed as a result of ligand binding. Unlike the EGF-receptor, four protein subunits are assembled where the kinase enzymes are separate protein subunits from the protein subunits acting as receptors. incorrect a.# The receptor is formed as a result of ligand binding. Correct b.# incorrect c.# incorrect d.# The kinase enzyme is a separate protein from the receptor protein. Phosphorylation of one half of the complex is catalysed by active sites on the other half. ATP is required for phosphorylation. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 40 40) What major role do intracellular receptors play? Feedback: The major role for intracellular receptors is to trigger transcription through the formation of a nuclear transcription factor. Correct a.# They trigger transcription. incorrect b.# They trigger replication. incorrect c.# They trigger translation. incorrect d.# They trigger reproduction. END OF QUESTION Type: multiple choice Title: Chapter 04 - Question 41 41) Which of the following statements is generally true regarding the chemical messengers for intracellular receptors? Feedback: Since the chemical messengers for intracellular receptors are extracellular, they have to be hydrophobic in order to cross the cell membrane. incorrect a.# They are hydrophilic in order to bind to zinc atoms. incorrect b.# They are hydrophilic in order to dissolve in the cell's cytoplasm. incorrect c.# They are hydrophobic in order to enter the nucleus of the cell. Correct d.# They are hydrophobic in order to cross the cell membrane. END OF QUESTION