Enzymes II
This session will cover:
How serine proteases such as chymotrypsin, trypsin and elastase
exhibit their substrate specificity substrate specificity.
How specific active site residues can accelerate a chemical reaction
How diffusion places an upper limit on the rate of enzyme reactions.
How protein motility and ATP are coupled in some life-essential
enzymes.
Key points:
Are enzymes perfect? How do we measure that?
How enzymes change the pathway of a reaction to make it faster, using the example of
serine proteases
The idea of enzymes acting as nanomachines – take energy from ATP (usually) and
change shape of enzyme to do mechanical work
Enzymes are proteins that speed up (catalyse) specific chemical reactions, they have
various functions include:
Digestion: Carbohydrates, fats, proteins
Blood clotting: fibrin clot catalysed by thrombin
Defence-immune system activation of complement
Movement: Muscle actomyo sin is an ATPase
Nerve conduction: Membrane ion pumps for Na+ and Ca2+
Key enzyme properties include:
-Increase reaction rate
-Show specificity
-Unchanged at end of reaction
-Do not alter reaction equilibrium
-Facilitate reaction by decreasing the free energy of activation of the reaction
Explaining further on from that last property of enzymes decreasing the free energy of
reaction. We know that in a chemical reaction where there is conversion of reactant to
product, it involves a change in the free energy of the reaction.
Whenever there is a drop in free energy from reactant to product, the reaction is
favourable, but to get to the product you have to put free energy in first which is like a
barrier. This amount of energy is the ‘free energy of activation’.
The highest point of the free energy of activation is the transition state.
Enzymes speed up reactions by reducing the free energy of activation, the enzyme
uses the binding energy of its substrate to lower the activation energy. This can be
seen below.
, We also categorise enzymes according to their kinetic parameters, there are two very
important parameters which are the:
Vmax = maximum rate of enzyme reaction
Km = A measure of how tightly the substrate is able to bind to the enzyme active site
We can represent this in a Michaelis-Menten curve, where we plot different substrate
concentrations against the reaction velocity. It develops the shape of an asymptote ->
This session will cover:
How serine proteases such as chymotrypsin, trypsin and elastase
exhibit their substrate specificity substrate specificity.
How specific active site residues can accelerate a chemical reaction
How diffusion places an upper limit on the rate of enzyme reactions.
How protein motility and ATP are coupled in some life-essential
enzymes.
Key points:
Are enzymes perfect? How do we measure that?
How enzymes change the pathway of a reaction to make it faster, using the example of
serine proteases
The idea of enzymes acting as nanomachines – take energy from ATP (usually) and
change shape of enzyme to do mechanical work
Enzymes are proteins that speed up (catalyse) specific chemical reactions, they have
various functions include:
Digestion: Carbohydrates, fats, proteins
Blood clotting: fibrin clot catalysed by thrombin
Defence-immune system activation of complement
Movement: Muscle actomyo sin is an ATPase
Nerve conduction: Membrane ion pumps for Na+ and Ca2+
Key enzyme properties include:
-Increase reaction rate
-Show specificity
-Unchanged at end of reaction
-Do not alter reaction equilibrium
-Facilitate reaction by decreasing the free energy of activation of the reaction
Explaining further on from that last property of enzymes decreasing the free energy of
reaction. We know that in a chemical reaction where there is conversion of reactant to
product, it involves a change in the free energy of the reaction.
Whenever there is a drop in free energy from reactant to product, the reaction is
favourable, but to get to the product you have to put free energy in first which is like a
barrier. This amount of energy is the ‘free energy of activation’.
The highest point of the free energy of activation is the transition state.
Enzymes speed up reactions by reducing the free energy of activation, the enzyme
uses the binding energy of its substrate to lower the activation energy. This can be
seen below.
, We also categorise enzymes according to their kinetic parameters, there are two very
important parameters which are the:
Vmax = maximum rate of enzyme reaction
Km = A measure of how tightly the substrate is able to bind to the enzyme active site
We can represent this in a Michaelis-Menten curve, where we plot different substrate
concentrations against the reaction velocity. It develops the shape of an asymptote ->
