Enzyme Kinetics Flashcards
Catalyst:
substance that increases the rate of a chemical reaction without being consumed in the reaction
provides an alternative pathway for the reaction in which the rate-determining step has a lower Gibbs activation energy than that of the non-catalysed reaction
Catalysis
- Does not appear in the overall equation for the reaction although it may appear in the rate equation
- Some substances slow down chemical reactions and these are often called negative catalysts or inhibitors
- Does not affect the amount of product formed—only the rate of its formation
- Small amount is usually needed
- Not changed chemically in the reaction and can be recovered at the end
- Sometimes may be changed physically
At a given temperature, the rate constant is greater for the catalysed reaction, so the reaction is ______
faster
Non-catalysed reaction proceeds through a _____ _______ state, whereas the mechanism for the catalysed reaction involves the formation of an intermediate
single transition
Enzyme-Catalysed reactions
Enzymes catalyse a wide range of reactions in biochemical systems
(human body dilute solution at 37 °C). Without the presence of enzymes, the reactions would take place much too slowly to sustain life.
Define enzymes;
protein molecules, catalyse a specific reaction, unchanged by
the reactions they catalyse
Whats the name of the model - enzyme and substrate bind?
Lock and Key Model
name of site on enzyme where substrate binds to?
Active site
Lock and key model - step by step
1) Substrate binds to enzyme (in active site) reversibly
2) Non-covalent interactions (enzyme-substrate complex) > reaction takes place
3) enzyme-product complex
4) product leaves to make free enzyme and free substrate
What INDUCED fit mean vs lock and key model
the active site of an enzyme will undergo a conformational change when binding a substrate, to improve the fit.
Chemical and shape compatibility of a substrate with an enzyme active site (substrate fits to active site precisely)
in the active sites what are two things that are present?
> hydrophobic region
charges +/-
Enzymatic reaction Profile -
Enzyme works as catalyst providing an _______ pathway for the reaction in which the rate-determining step has a lower ______ activation energy than that of the non-catalysed reaction
alternative
Gibbs
LOWER the activation energy…
more sufficient the reaction is = the FASTER the rate of reaction
Two distinct steps in enzyme catalysed reaction:
1) first step - reversible
2) second step - irreversible
Michaelis Menten model was developed to understand the kinetics of enzymic reactions.
E + S <> (k1/k-1)
ES > E + R (k2)
A number of assumptions are applied to the Michaelis Menten model:
The enzyme binds a single substrate (the model assumes cofactors are already bound)
There are two distinct steps. The substrate binds reversibly but product formation is irreversible
A steady state approximation applies (quantitative analysis of the kinetics of enzyme-catalysed reactions)
Whats the name of the state at the strart of an enzymatic reaction?
The steady state
Rate of formation of ES = Rate of consumption of ES (conversion to E + P)
( 𝒅[𝑬𝑺])/𝒅𝒕=(Rate of formation of ES - Rate of consumption of ES)=0
=k1 [E] [S] -k2 [ES] - k-1 [ES]
( 𝒅[𝑬𝑺])/𝒅𝒕=k1 [E] [S] –(k2 - k-1 )[ES]=0
Assumption is made that: [E]0 = [ES] + [E] where [E]0=
total conc of enzyme
Concentration of the substrate is usually much larger than that of the enzyme, so that [S] is effectively ______
constant
In the initial phase of the reaction: [E]^ and [ES]^
[ES] and [E] remain steady over most of the reaction time.
Only at the end of the reaction, when [S] is exhausted, does [ES] decline
The Michaelis Menten Equation
𝑽 (𝒓𝒂𝒕𝒆 𝒐𝒇 𝒓𝒆𝒂𝒄𝒕𝒊𝒐𝒏)= ( 𝑽𝒎𝒂𝒙 [𝑺])/(𝑲𝑴+[𝑺])
What kind of linear when the velocity of an enzyme catalysed reaction increases
a non-linear fashion
