[FMS] CBS - enzymes Flashcards
are enzymes stabilised by weak or strong bonds?
weak bonds
which one of these is NOT weak bond involved in enzymes
H-bonds,
electrostatic salt bridges
Van der Waals
ionic bonds
hydrophobic interactions.
ionic bonds
strong bonds = HHEV
who made the lock and key theory and what is it?
Emil Fisher 1884 - enzymes are complementary to their substrate explaining high specificity but misleading
who made the induced fit theory and what is it?
Induced Fit: Daniel Koshland 1958 - enzymes undergo conformational change upon substrate binding induced by weak interactions with substrate
what is enzyme specificity determined by?
Determined by cleft or groove of defined shape - the ‘active site’ into which only the substrate of correct shape and charge can fit
What is a transition state? if you stabilise the transition state what happens to the enzyme?
An unstable, high-energy intermediate in a chemical reaction:
stabilising the transition state is one way that enzymes can speed
up a reaction
the enzyme must be complimentary to what?
the transition state
how many enzyme classes are there? what are they called?
6:
oxidoreductases
transferases
hydrolases
lyases
isomerases
ligases
what does an oxidoreductase do? give an example?
what does a transferase do? give an example.
what does a hydrolase do? give an example.
what does a lyase do? give an example.
what does a isomerase do? give an example.
what does a ligase do? give an example.
how are enzymes classified?
by a 4 digit number
effect of temp on enzymes
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).
DIRECT effect of ph on enzyme-controlled reactions?
[H+] or [OH-] appear in rate equation
2 SUBSTRATE effects of ph on enzyme-controlled reactions?
- changes in ionisation state of substrate = additional acid/base catalysis
- changes leading to altered binding to enzyme =change in Km
2 effects of ph ON ENZYME controlled reactions?
- 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).
what is enzyme kinetics
The study of the rate of an enzyme catalysed reaction
what is the Michaelis Menten equation
whats the shape of Michaelis menten equation on a graph
hyperbolic curve
V0
initial reaction velocity, measured as soon
as enzyme and substrate are mixed.
what is Vmax and where is it found
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.
what is Km, where is it found on graph
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
what is [S]
= substrate concentration
when V0 = 0.5Vmax …
Km = [s]
what is Kcat
number of substrate molecules converted to product in a unit of time on a single enzyme molecule when the enzyme is saturated with substrate.
3 assumptions of Michaelis Menten
3 assumptions:
- [S] > [E] so amount of substrate bound by enzyme at any one time is small
- Initial velocities used, concentration of product small so back reaction (k2) is small = ignored
- [ES] does not change with time (steady-state) - formation ES = breakdown ES:
how to compare catalytic efficiency
Kcat/Km
lineweaver burk plot equation
on the Lineweaver Burk plot, where is 1/Vmax
y axis
on the Lineweaver Burk plot, where is -1/Km
x axis
in enzyme inhibition, what does a competitive inhibitor do to Km and Vmax
increase Km
same Vmax
in enzyme inhibition, what does a non-competitive inhibitor do to Km and Vmax
same Km
decrease Vmax
what 2 things do competitive inhibitors do? give an example
block the enzyme active site
interfere with catalytic mechanism
2 types of irreversible enzyme inhibitors
*AChE (Acetylcholinesterase)
inhibitors
* organophosphates
- Insecticides
- Nerve agents NOVICHOK
shape of graph for allosteric modulation
sigmoidal
in allosteric enzyme kinetics, what does a high Km value correspond to?
t-state
in allosteric enzyme kinetics, what does a low Km value correspond to?
R-state
when would you have a positive or negative allosteric modulator>
describe the covalent modification of enzymes
reversible addition/removal of phosphate from SER/THR/TYR/HIS residues by kinase/phosphatase enzymes - active or inactive:
How do allosteric enzymes regulate enzyme activity
end product of the metabolic pathway is an allosteric inhibitor to the beginning of the pathway, controlling the production of the end product
do keats quiz on enzymes
https://keats.kcl.ac.uk/mod/quiz/view.php?id=7540181
What is the relationship between the kinetic properties of an enzyme (Vmax and Km) and the affinity of the enzyme for its
substrate?
An enzyme with a low Km has a high affinity for its substrate irrespective of the Vmax of the enzyme
