Enzyme Chemistry Flashcards
Define enzyme
a protein molecule that accelerates a specific chemical reaction
What do enzymes do?
Enzymes are catalysts
Proteins that facilitate reaction mechanisms
Catalyse specific reactions
Increase rate of reaction
Define active site
the region of an enzyme that binds the substrate during a chemical reaction.
Define substrate
the reactant(s) in enzyme-catalysed reaction.
What are the key features of the active site?
Small relative to the total volume of the enzyme.
Usually occur in clefts and crevices of the protein.
Amino acids and cofactors are held in precise arrangement with respect to the substrate.
Amino acids in the active site define specificity.
Why use enzymes as catalysts?
Higher reaction rate.
Milder reaction conditions - neutral pH, atmospheric pressure and close ambient temperature.
Greater specificity (in terms of substrate and products not by-products)
There is capacity for control - they respond to concentration of substances.
How do enzymes bind substrates?
Lock and key model
Induced fit
Transition state stabilisation
Explain the lock and key model
The structure of the active site is complementary to the substrate (like a lock to it’s key).
The shape of the active site is determined by the tertiary and quaternary structure of the protein.
Explain the induced fit mechanism
Certain enzymes can catalyse similar reactions.
The induced fit model suggests that the active site of the enzyme undergoes a conformational change when the substrate binds to be a perfect fit for the substrate.
eg. Hexokinase converts glc to glc-6-p
What is substrate specificity determined by?
The active site is complementary to the structure of the substrate (geometric).
The amino acids in the active site interact specifically with the substrate (electronic). If amino acids (AAs) on the substrate are negative then the active site will contain positively charged AAs. If the AAs on the substrate are hydrophobic then the active site will contain hydrophobic AAs.
What is stereospecificity in terms of enzyme catalysis?
Enzymes will only bind ONE stereoisomer, eg. only the R form and not the S.
Stereospecificity is due to the active site of the enzyme.
Define chiral
Two mirror images that are non-superimposable
What are the six classes of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
What are cofactors?
Small molecules that some enzymes require during catalysis. They can be metal ions or organic molecules (coenzymes).
What is a co-substrates?
Are associated transiently with the enzyme - goes into the active site to facilitate the reaction and then leave the active site to be regenerated. Eg ATP.
What is a cofactor know as?
These are known as prosthetic groups and are tightly bound to the enzyme
What is a holoenzyme?
A catalytically active enzyme-cofactor complex
What is an apoenzyme
An inactive protein due to the absence of a cofactor
Can metal ions behave as co-substrates or prosthetic groups?
No only co enzymes (organic molecules) can do this.
What is a first order reaction?
One molecule changes to another A -> B v = velocity
v = k[A]
What is a second order reaction?
Two molecules react A + B -> P + Q
2A -> P
v = k[A][B]
v = k[A]^2
What is the equation that gives the [A]? (first order)
[A] = [A]oe^-kt
What do oxidoreductases catalyse? Give an example.
- redox reactions
- transfer hydrogen/oxygen/electrons between substrates
- example is alcohol dehydrogenase
What do transferases catalyse? Give an example.
- transfer of functional groups between substrates
- example is hexokinase
