Enzymes, Kinetics and Inhibition Flashcards
enzyme
is a biological catalyst
Biological
Most enzymes= globular proteins (mostly spherical and water soluble)
Can have Abzymes
other options:
Ribozymes
DNAzymes
Catalyst
Accelerates rate of reaction
Doesn’t get involved
> Wear out/ don’t last forever
Acts on some other molecule/substance
what are enzyme reactions
enzyme reactions are ‘specialised’ chemical reactions
chemical reactions
Reactants are converted into products.
May involve a catalyst.
Rate of reaction can be measured.
Rate increases as temperature increases essentially without limit.
Enzyme Reactions
Substrates are converted into products.
Always involves a catalyst (the enzyme).
Rate of reaction can be measured.
Rate increases as temperature increases up to a limit.
Active site
A particular region where the other molecule binds.
Has a 3D conformation.
Enzyme Kinetics
area of study involving measuring the rates of reaction of enzymes.
the catalytic rate constant
is the rate constant for the conversion of ES into EP
ES complex
can dissociate back into E and S without formation of P
Km
is the [S] which will give a velocity equal to half the Vmax
The Michaelis-Menten Equation
Allows us to calculate the expected velocity at a given [S] as we have established the Vmax and Km for an E/S reaction pair.
The Law of thermodynamics
> The rate of any chemical reaction is sensitive to temperature.
An increase in temperature leads to an increase in reaction rate.
A common rule of thumb is that a 10 degrees increase doubles the rate of a reaction.
what is pH ?
is a measure of acidity
what terminals do proteins contain?
N-terminal = NH3 group
C-terminal = COOH group
key effect of pH on enzyme activity is mediated by ….
changes in the charge state of amino acids involved in the catalytic reaction.
active from of enzymes
only when the R1 side chain is pronated and the R2 is not.
the pH optimum
the pH the enzyme works best at
substrates can become ionised meaning
the overall charge on a substrate may influence which enzymes can act on it.
examples of substrates that may be charged
Organic acids
Phosphate esters
Nucleotides
why do we call enzymes inhibited ?
when the enzyme cannot complete a catalytic cycle.
net effect =
= reduced conversion of S —> P
In kinetic terms:
The velocity of a reaction decreases
Reaction does proceed but not as quickly
Something gets in the way –> the inhibitor, I
Reversible inhibition
Inhibitor can bind to and dissociate from the enzyme.
Activity is lost when inhibitor is bound.
Wait for enzyme to become free to overcome.
Irreversible inhibition
Enzyme is covalently modified and activity lost.
Replace enzyme to overcome.
Reversible inhibition forms:
Competitive
Uncompetitive
Mixed
Competitive inhibition
Inhibitor binds at the active site.
Prevents substrate binding.
Uncompetitive inhibition
Inhibitor binds to the EScomplex.
Not at active site.
Mixed inhibition
The inhibitor can bind to the free enzyme or the EScomplex.
Aspirin
the classic suicide inhibitor
Irreversibly inactivates an cyclooxygenase II
Involved in prostaglandin synthesis.
!!!!!
At high [S] the excess P formed leads to inhibition.
what has roles to overcome activation energy
Proximity
Distortion
!!!!
velocity of a reaction increases when [S] increases
!!!!!!!!
The Km is the [S] which will give 1/2Vmax
Enzyme inhibitors
block enzyme action
