BMS1030 - Enzymes Flashcards
Give some examples of enzymes in industry.
Rennet -> a mix of enxymes used in cheesemaking
Invertase -> breaks down hard suagrs into soft sugars (making soft-centred chocolate)
What is a ribozyme?
An enzyme made from RNA.
What are cofactors?
Extra molecules or ions that are needed for the activity of some enzymes.
Very commonly metal ions like Zn2+, Fe2+ or Mg2+.
Often found in enzymes that catalyse redox reactions.
What is a coenzyme?
A more complex, organic cofactor. Derived from vitamins. Often act as carriers for functional groups.
e.g. NAD (carries H-)
Coenzyme A (carries Acyl groups)
What can prosthetic groups and cosubstrates soometimes be called?
Coenzymes
Although coenzymes bind much more loosely than prothetic groups.
What is an apoenzyme?
The inactive enzyme, before cofactors bind.
What is a holoenzyme?
The active enzyme, after cofactor has bound. Now able to bind to substrate.
What is the equation for Gibbs Free Energy? What is it?
G = H - TS
H (heat), T (Temp in K), S (Entropy)
How does alcohol dehydrogenase use cofactors in its catalytic function?
Ethanol + NAD+ —> Acetaldehyde + NADH
What is the ground and transition state?
Ground State = The energy of level of ‘resting’ substrate or product.
Transition State = the activated form of the moelcule at the top of the ‘energy hill’
In enzymatic reactions, intermedites are introduced. How does this affect the transition state and rate?
The activation energies required to produce these intermeidates are lower so the transition states is at a lower energy level, so rate of reaction increases.
How do enzymes lower the activation energy of a reaction?
Putting strain on the bonds in a substrate so less energy is needed to break them.
What does a catalyst do and how?
Increases the rate of reaction without being consumed by the reaction.
By lowering the activation energy.
Most enzymatic reactions are at _________.
Equilibrium
What is the rate-limiting step?
The step with the highest activation energy - the reaction can only go as fast as the RLS.
Note: if all steps have similar activation energy then all steps are rate-limiting.
What is the importance of binding energy (ΔGB) in enzymatic reactions?
binding energy = the energy of all weak interactions (e.g. H-bonds, ionic interactions, hydrophobic effect) added up.
Used to lower the activation energy of the reaction.
How does binding energy (ΔGB) explain enzyme specificity?
The ‘wrong’ substrate won’t form
the right interactions, so won’t release sufficient binding energy.
When are weak interactions in the formation of ESCs optimised?
In the transition state as the substrate is changing into the product.
What is induced fit?
When the enzyme undergoes conformational change when ESCs –> EPCs
Enzymes bind preferentally to the __________ state of a substrate.
Transition
In what other ways do enzymes help reactions?
ENTROPY REDUCTION - restricting movement of substrates making it more likely that they will colide and react.
REMOVAL OF SOLVATION SHELL - substrate binding to enzyme usually loses its ‘shell’ of water molecules that may block reaction sites.
DISTORTION OF SUBSTRATES - binding energy can be used to ‘twist’ substrates into the right orientation.
ALIGNMENT OF FUNCTIONAL GROUPS to aid the reaction
What is V0? What happens to it as you increase [S]?
Initial velocity - the rate of the reaction at the beginning (before all initial substrate is used up).
As [S] increases, V0 increrases but by a small amount. Eventually increasing [S] has no further impact on the reaction rate - reaction is at Vmax.
What is Vmax?
Maximum velocity (of a reaction)
When the enzyme is saturated
What is on the y and x axis of a Michaelis-Menten plot?
x axis = Initial velocity ((μM/min)
y axis = Substrate concentration (nM)
