[FMS] CBS - enzymes

Question 1

are enzymes stabilised by weak or strong bonds?

Answer 1

weak bonds

Question 2

which one of these is NOT weak bond involved in enzymes

H-bonds,
electrostatic salt bridges
Van der Waals
ionic bonds
hydrophobic interactions.

Answer 2

ionic bonds

strong bonds = HHEV

Question 3

who made the lock and key theory and what is it?

Answer 3

Emil Fisher 1884 - enzymes are complementary to their substrate explaining high specificity but misleading

Question 4

who made the induced fit theory and what is it?

Answer 4

Induced Fit: Daniel Koshland 1958 - enzymes undergo conformational change upon substrate binding induced by weak interactions with substrate

Question 4

what is enzyme specificity determined by?

Answer 4

Determined by cleft or groove of defined shape - the ‘active site’ into which only the substrate of correct shape and charge can fit

Question 5

What is a transition state? if you stabilise the transition state what happens to the enzyme?

Answer 5

An unstable, high-energy intermediate in a chemical reaction:
stabilising the transition state is one way that enzymes can speed
up a reaction

Question 6

the enzyme must be complimentary to what?

Answer 6

the transition state

Question 7

how many enzyme classes are there? what are they called?

Answer 7

6:

oxidoreductases
transferases
hydrolases
lyases
isomerases
ligases

Question 8

what does an oxidoreductase do? give an example?

Answer 8

Question 9

what does a transferase do? give an example.

Answer 9

Question 10

what does a hydrolase do? give an example.

Answer 10

Question 11

what does a lyase do? give an example.

Answer 11

Question 12

what does a isomerase do? give an example.

Answer 12

Question 13

what does a ligase do? give an example.

Answer 13

Question 14

how are enzymes classified?

Answer 14

by a 4 digit number

Question 15

effect of temp on enzymes

Answer 15

Weak bonds stabilising structures are easily broken by heating protein giving rise to disorganised/tangled structure in which enzyme has no catalytic activity (denatured/inactive).

Question 16

DIRECT effect of ph on enzyme-controlled reactions?

Answer 16

[H+] or [OH-] appear in rate equation

Question 17

2 SUBSTRATE effects of ph on enzyme-controlled reactions?

Answer 17

• changes in ionisation state of substrate = additional acid/base catalysis
• changes leading to altered binding to enzyme =change in Km

Question 18

2 effects of ph ON ENZYME controlled reactions?

Answer 18

• unfolding of the enzyme leading to complete inactivation
• changes in ionisation state of active site residues leading to change in Km (substrate binding) or Vmax (involved in reaction).

Question 19

what is enzyme kinetics

Answer 19

The study of the rate of an enzyme catalysed reaction

Question 20

what is the Michaelis Menten equation

Answer 20

Question 21

whats the shape of Michaelis menten equation on a graph

Answer 21

hyperbolic curve

Question 22

V0

Answer 22

initial reaction velocity, measured as soon
as enzyme and substrate are mixed.

Question 23

what is Vmax and where is it found

Answer 23

maximal velocity of an enzyme
catalysed reaction i.e. when all the enzyme
active sites are fully saturated with substrate

found on top of graph.

Question 24

what is Km, where is it found on graph

Answer 24

Michaelis constant Km= (k-1 + k2)/k1 Therefore Km is the substrate concentration at **half maximum velocity of the reaction** found on x axis at bottom of graph

Question 25

what is [S]

Answer 25

= substrate concentration

Question 26

when V0 = 0.5Vmax ...

Answer 26

Km = [s]

Question 27

what is Kcat

Answer 27

number of **substrate molecules** converted to **product** in a unit of time on a single enzyme molecule when the enzyme is saturated with substrate.

Question 28

3 assumptions of Michaelis Menten

Answer 28

***3 assumptions:*** 1. [S] > [E] so amount of substrate bound by enzyme at any one time is small 2. Initial velocities used, concentration of product small so back reaction (k2) is small = ignored 3. [ES] does not change with time (steady-state) - formation ES = breakdown ES:

Question 29

how to compare catalytic efficiency

Answer 29

Kcat/Km

Question 30

lineweaver burk plot equation

Answer 30

Question 31

on the Lineweaver Burk plot, where is 1/Vmax

Answer 31

y axis

Question 32

on the Lineweaver Burk plot, where is -1/Km

Answer 32

x axis

Question 33

in enzyme inhibition, what does a competitive inhibitor do to Km and Vmax

Answer 33

increase Km same Vmax

Question 34

in enzyme inhibition, what does a non-competitive inhibitor do to Km and Vmax

Answer 34

same Km decrease Vmax

Question 35

what 2 things do competitive inhibitors do? give an example

Answer 35

block the enzyme active site interfere with catalytic mechanism

Question 36

2 types of irreversible enzyme inhibitors

Answer 36

*AChE (Acetylcholinesterase) inhibitors * organophosphates - Insecticides - Nerve agents NOVICHOK

Question 37

shape of graph for allosteric modulation

Answer 37

sigmoidal

Question 38

in allosteric enzyme kinetics, what does a high Km value correspond to?

Answer 38

t-state

Question 39

in allosteric enzyme kinetics, what does a low Km value correspond to?

Answer 39

R-state

Question 40

when would you have a positive or negative allosteric modulator>

Answer 40

Question 41

describe the covalent modification of enzymes

Answer 41

reversible addition/removal of phosphate from SER/THR/TYR/HIS residues by kinase/phosphatase enzymes - active or inactive:

Question 42

How do allosteric enzymes regulate enzyme activity

Answer 42

end product of the metabolic pathway is an allosteric inhibitor to the beginning of the pathway, controlling the production of the end product

Question 43

do keats quiz on enzymes

Answer 43

https://keats.kcl.ac.uk/mod/quiz/view.php?id=7540181

Question 44

What is the relationship between the kinetic properties of an enzyme (Vmax and Km) and the affinity of the enzyme for its substrate?

Answer 44

An enzyme with a **low Km has a high affinity** for its substrate **irrespective of the Vmax** of the enzyme