1. Which of the following is not true of transition-state analogues? a) They mim
ID: 714913 • Letter: 1
Question
1. Which of the following is not true of transition-state analogues? a) They mimic the transition state of an enzyme-catalysed reaction. b) They react irreversibly with the enzyme c) They are bound more strongly than the substrate or the product. d) They require the presence of a stable functional group to mimic the functionality present in the transition state. 2. Which of the following agents act as irreversible inhibitors? a) sulphonamides b) penicilllins c) statins d) protease inhibitors 3. Which of the following functional group is likely to be the strongest hydrogen bond donor? a) alcohol b) amine e) phenol d) ammonium ion 4. Which of the following terms is the measure of how strongly a drug binds to a receptor? a) affinity b) efficacy c) potency d) stability 5. Which of the following is not a crucial requirement for a drug to act as an agonist? a) Functional groups b) Metabolic stability c) Pharmacophore d) SizeExplanation / Answer
1) Transition state analogues :
Transition state analogues are the chemical compounds that are similar to the structure of the transition state of an enzyme catalysed reaction. When substrate bind to the enzyme, it undergoes geometrical changes to form unstable transition state. Transition state analogues have high affinity to bind much more stronger than the substrate, inorder to deactive and inhibit the enzyme from binding with substrate. It reacts irreversibly in which a modified substrate can bind to the enzyme and inhibits the formation of products. Transition state analogues mimics the high energy intermediate but does not undergo chemical reaction in enzyme catalysed reaction. These are designed using kinetic effect and computational simulation on complex compounds.
So, the answer which is not true is option d).
2) Irreversible Inhibitors : Irreversible inhibitors binds the enzyme through covalent or non-covalent bond chemically and slowly dissociates from the enzyme.
In the given inhibitors, sulphonamides competitively binds to dihydropteroate synthase (DHPS) enzyme which sythesizes the folic acid. Sullphonamides is a competitive inhibitor.
Pencillin binds at the active site of transpeptidase enzyme which cross links the peptidoglycan strands. It irreversibly inhibits the enzyme transpeptidase by reacting with a serine reside in transpeptidase enzyme. So, pencillin is irreversible inhibitor.
Statins are reversible inhibitor which binds to the HMG Co-A reductase.
Protease are the reversible inhibitors which blocks the activity of proteases.
So, option b) is correct answer.
3) Hydrogen bond donor is defined as the atom to which the hydrogen atom participating in the hydrogen bonding is covalently bonded such as electronegative atoms like N,O and F. Among alcohols and amines, alcohols are strong hydrogen bond donor than amines because of high electronegativity of oxygen atom. In phenols, lone pair of electrons on oxygen atoms are drawn into the benzene ring increases the electron density of the ring system. Alcohols having alkyl group attached to the oxygen atom causing oxygen to be more electron dense. In water, phenol acts as strong acid and alcohol acts as weaker acid than phenols. So, hydrogen bonding is stronger in phenols. So, option c) phenol is correct.
4) option 1) is correct.
1) Affinity is the term to measure how strong a drug can bind to a receptor.
2) Efficacy is the relationship between the receptor occupancy and the ability to initiate a response at cellular, tissue level in system.
3) Potency is a measure of the drug concentration to produce an effect of given intensity.
4) Stability is the ability of the drug to maintain the properties during the time storage and usage by the patient.
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