Enzymes Flashcards
What do proteases do?
Degrade proteins
What do phosphatases do?
Remove phosphates
What do ribonucleases do?
Cleave RNA molecules
How doe enzymes work?
They lower the activation energy required for the molecular reaction to take place.
What are co-factors?
Non-protein molecules which assist in the biochemical transformation
What are the two classes of co-factors?
- Coenzymes
- Prosthetic groups
What are the differences between the two classes of co-factors?
- Coenzymes are loosely bound
- Prosthetic groups are tightly bound
What do prosthetic groups do?
They act as activators and/or inhibitors of activity.
What do coenzymes do?
- They catalyse reactions.
- Transfer electrons
- Form/break a covalent bond
- Transfer a group
What are examples of coenzymes?
- NAD+ / NADH
- Coenzyme A
- Vitamins
What are examples of prosthetic groups?
They are small inorganic ions.
- Mg
- Mn
- Fe
- Zn
- Cu
When are enzymes most stable?
In a transition state
How does temperature affect enzymes?
- Temperature causes the rate of interactions to go up; therefore the rate of catalysis goes up
- However, higher temperatures cause denaturation of the enzyme - The shape changes; therefore loses its activity
How does the substrate concentration affect enzyme activity?
- Increasing the concentration of substrate increases the rate of reaction fairly linear, the enzyme is processing the substrate quicker than the substrate can find the enzyme
- The rate of reaction stops increasing at a certain point as the enzyme is full when the substrate meets it because there’s so much substrate there, the collisions is now faster than the enzyme can process the substrate
- At this point adding more substrate will not change anything as the enzyme is already full.
In terms of Michaelis-Menten kinetics, what does V mean?
Mols of product per second (the rate of the catalytic reaction)
In terms of Michaelis-Menten kinetics, what does Vmax mean
The maximum observed rate
What happens at high substrate concentrations [S] in terms of V and S?
V is nearly independent of S
In terms of Michaelis-Menten kinetics, what does S mean?
Substrate concentration
In terms of Michaelis-Menten kinetics, what does ES mean?
Enzyme substrate
In terms of Michaelis-Menten kinetics, what does EP mean?
Enzyme product
What is the Michaelis-Menten equation for an enzyme product?
E + S –> ES –> Ep
E + S –> ES is reversible
In terms of Michaelis-Menten kinetics, how do you determine the rate of formation of EP?
[ES]
V = K3[ES]
In terms of Michaelis-Menten kinetics, how do you determine the rate of formation of ES?
[E][S]
V = K1[E][S]
In terms of Michaelis-Menten kinetics, how do you determine the rate of breakdown of EP?
V = (K2+K3)[ES]
What is the Michaelis equation when under steady conditions [ES] is constant whilst substrate and product may vary?
[E][S]=[ES]
- Rate of breakdown = Rate of formation
- K1 [E][S] = (K2+K3)[ES]
How do you calculate Km?
(K2+K3)/K1
Units is mol dm3
What is the Michaelis-Menten equation involving Km?
[ES] = ([E] [S]) / Km
In terms of Michaelis-Menten kinetics, what does ET stand for?
Total enzyme
What is the Michaelis-Menten equation involving ET?
[ES] = [ET] x [S] / ([S] + Km)
What is the main Michaelis-Menten equation?
V = Vmax x [S] / ([S] + Km)
If [S] «_space;Km then…
Rate is proportional to [S]
V = Vmax ([S] / Km)
If S = Km then…
Rate is half Vmax
V = Vmax ([S] / ([S] +[S])) =Vmax / 2
If [S]»_space; Km then…
Rate is Vmax
V = Vmax [S] /[S] = Vmax
In terms of Michaelis Menten what is K2?
K2 is going from ES back to E + S
In terms of Michaelis Menten what is K3?
k3 is going from Es –> EP
How do enzymes lower activation energy?
- An enzyme molecule must interact specifically with the substrate molecule or a small number of closely related substrates
- The molecule (or substrate) fits within a particular cavity on the enzyme (active site) and is attracted to particular points of charge within the cavity
Binding substrate
E + S <-> ES
Substrate converted to bound product
ES <-> EP
Release of product
E + P
What is activation energy?
Barrier to spontaneous reaction
What stabilises the transition state complex?
Diverse interactions
At a low concentration of substrate…
- The catalytic site of the enzyme is empty, waiting for the substrate to bind.
- The rate at which product can be formed in limited by the concentration of substrate available.
Competitive inhibition
Inhibition competes reversibly with substrate for active site
Uncompetitve inhibition
Inhibitor binds only to the Es complex leading to EIS intermediates. This is very rare
Non-competive inhibition
Allosteric
Inhibitor binds non-covalently to sites other tan the active site.
Partially inhibited enzymes can still turn over substrate
Irreversible inhibition
Irreversible inhibitors form covalent or very tight bonds with functional groups in active site.
