Enzymes Flashcards
What is a cofactor?
Non-protein component of enzymes that are needed for activity
What is a coenzyme?
A complex organic molecule usually formed from vitamins
What is a prosthetic group?
Cofactor covalently bound (or very tightly associated) to an enzyme
What is an apoenzyme?
Protein component of an enzyme containing a prosthetic group
What is a holoenzyme?
The whole enzyme
How to enzymes catalyse reactions?
They increase the rate of spontaneous reactions, lower activation energy and accelerates movement towards equilibrium
What do spontaneous reactions contain?
An energy barrier
What happens as [S] increases?
The initial velocity increases up to Vmax
What is the shape of the initial rate in a [S] vs Vo graph when the [enzyme] is much lower than [substrate]?
Hyperbolic
What is Vo?
The initial reaction velocity that is the steady state of a reaction
What is Vmax?
The maximum reaction velocity, when all the active sites are saturated by substrate
What is Km?
Michaelis constant
What is the function of Km?
Measures an enzymes affinity for its substrate
What is the affinity when Km is low?
High
What is the affinity when Km is high
Low
What does the Michaelis-Menton (M-M) equation tell us?
Km= 1/2Vmax= (k-1 + k2)/k1
What does k1 determine?
The overall rate
What is k2?
It is slower than k1 and is reversible
What is the M-M equation useful for?
Measuring Vo and Vmax
What are the 3 types of enzyme inhibitors?
Competitive, non-competitive and uncompetitive
What is a competitive inhibitor?
An inhibitor that binds non-covalnetly to the active site. Their affect is overcome by high substrate concentrations and they mimic the substrate. They do not affect Vmax
Can Vmax still be achieved in competitive inhibition?
Yes as it is overcome by high substrate concentrations
What affect does competitive inhibition have on Km?
It increases Km, decreasing affinity for the substrate
What is a non-competitive inhibitor?
It is an inhibitor that binds non-covalnety to the allosteric site. They are not overcome by high substrate concentrations
What affect does non-competitive inhibition have on Km?
It is unchanged as substrates can still bind to the active site
What affect does non-competitive inhibition have on Vmax?
Vmax decreases as the inhibitor can’t be displaced
What is an uncompetitive inhibitor?
An inhibitor that binds to the complex formed by the enzyme and substrate
What affect does uncompetitive inhibition have on Km?
It decreases
What affect does uncompetitive inhibition have on Vmax?
It decreases
What is an enzyme assay?
A method of measuring enzyme activity for clinical diagnosis
What regulates enzyme activity?
Allosteric effectors
What are allosteric effectors?
They can be inhibitors or activators that enable changes in the ICE and ECE which changes the flow of metabolic pathways
What are allosterically-regulated enzymes?
Multimeric proteins in which a conformational change in one of the polypeptides affects the whole the protein
What is a multimeric protein?
Many polypeptides held together
What is the shape of the initial reaction rate against [S] graph fro allosterically-regulated enzymes?
Sigmoidal
What is an example of a reaction that would produce a sigmoidal curve?
When oxygen binds to haemoglobin
What is reversible covalent modification?
Modification in amino acid side chains which affects enzyme activity
