lecture 07

Question 1

purpose of an enzyme

Answer 1

increase rate of reaction without changing the equilibrium by lowering the activation energy of a reaction at transition state

Question 2

are catalysts specific

Answer 2

yes

Question 3

how do catalysts accelerate reactions

Answer 3

they stabilise the transition state to make it energetically favourable

Question 4

give methods of enzyme catalysis

Answer 4

enzyme must provide a reaction surface and suitable environment ( hydrophobic).
It can either: bring reactants and substrates together, position reactants correctly for the reaction , weaken bonds in the reactants or participate in the reaction mechanism

Question 5

describe an active site

Answer 5

small hydrophobic hollow which contains amino acids wich bind reactants to catalyse a reaction

Question 6

Acid catalyst example

Answer 6

ionised histidine, unionised glutamic acid

Question 7

basic catalyst example

Answer 7

non - ionised histidine , ionised glutamic acid

Question 8

explain how the catalytic triad works

Answer 8

aspartate shares H with the NH in histidine leaving a lone pair of electrons at the other N. This allows His to take hold of the H in serine, leaving serine with an o- charge , making it a strong nucleophile.

Question 9

why is lysine not usually used as a nucleophile

Answer 9

protonated at physiological pH - but if its in a hydrophobic pocket of an enzyme it wont be protonated, allowing it to be used.

Question 10

which bond does ACE cleave

Answer 10

2nd amide bond in from the carboxyl terminus - between a Phe and a His

Question 11

what grouping is required in ace catalysis

Answer 11

histidine, glutamate and zinc grouping - this holds the position of the peptide

Question 12

un competitive inhibition

Answer 12

can only bind in presence of substrate. Binds to a substrate enxyme complex to keep it in place avoiding release of products?

Question 13

non-competitive inhibiton

Answer 13

can bind in presence or absence of substrate binds to different site

Question 14

explain the function of the glutamate basic site and zinc in the active site of ACE

Answer 14

it accepts a proton from water, meaning the deprotonated water can cause nucleophilic attack of the peptide carbonyl. The zinc stabilises the accumulated charge on the =O. Then the tetrahedral intermediate collapses and the amine deprotonates the glutamate.

Question 15

what initiates elimination in the breakdown of Ag1 to Ag2

Answer 15

oxyanion, this cleaves the peptide bond ( 2nd in from c terminus)

Question 16

what kind of inhibitor is captopril

Answer 16

competitive

Question 17

what does methotrexate do , and how is it different to fluoruracil

Answer 17

they both inhibit dihydropholate reductase. In methotrexate this is reversible, but irreversible for fluoruracil.

Question 18

what does it mean if EC50 and IC50 are equal

Answer 18

the drug completely inhibits biological activity

Question 19

what is EC 50

Answer 19

conc of drug which gives 50% of the maximum response

Question 20

what are activators

Answer 20

ligands which switch on enymes by binding at allosteric sites. some stabilise a specific enzyme conformation. This either increases turnover or lowers the activation energy

Question 21

whats an inverse agonist

Answer 21

they decrease endogenous activity

Question 22

whats an agonist do to a reaction

Answer 22

activate receptors

Question 23

positive allosteric modulator

Answer 23

increases orthosteric activity

Question 24

neutral allosteric modulator

Answer 24

no effect but blocks other allosteric ligands

Question 25

whats Kd

Answer 25

dissociation constant - eg ratio of a ligands on and off binding

Question 26

whats Ki

Answer 26

inhibition constant - binding of inhibitor on and off the enxyme

Question 27

whats Km

Answer 27

michaelis constant - conc of substrate that gives half of the max enxymatic reaction rate

Question 28

what is EC50 a measure of in general

Answer 28

potency of a drug