Enzymes II
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How do enzymes catalyze reactions?
• Conversion of reactants to products, reacting molecules must overcome energy barrier. • Enzymes facilitate reactions by reducing the energy barrier. • E enhance reactions by binding with S to form complex with a lower ΔG*: E + S <==> ES –> E + P
What are the theories about how enzymes work?
o Collision theory o Transition state theory
What is a transition state theory?
the free energy in this state is much higher than the free energy in the substrate free energy, finally the new bond will form to make new products. For a reaction to happen, there should be enough energy to carry the substrate to the transition state (activation energy)
The free energy that the substrate need to get to the transition state is called the _______
ACTIVATION ENERGY
_____ is the minimum amount of energy required to overcome the energy barrier to get to the activated complex of the transition state.
DELTA G
_____ symbolizes the minimum amount of energy required to overcome the energy barrier to get to the activated complex of the transition state.
DELTA G
True/False The larger the activation energy is the more difficult for the reaction to occur
True
Enzymes as a type of catalysis accelerate chemical reaction by lowering the _______.
activation energy
The collision theory
If molecules move too slowly with little kinetic energy, or collide with improper orientation, they do not react and simply bounce off each other. However, if the molecules are moving fast enough with a proper collision orientation, such that the kinetic energy upon collision is greater than the minimum energy barrier, then a reaction occurs
How do enzymes lower the activation of energy?
Enzyme can transiently bind with the substrate to produce a transition state “E-S” having a lower activation of energy than the transition state of the uncatalyzed reaction
How can we measure the enzyme activity?
Reaction rate of enzymatic reaction
How can we measure the reaction rate?
The rate of disappearance of substrate or The rate of the formation of product (normally this is used bc it is quite reliable)
Give examples for the initial rate experiments
continuous method discontinuous method
Continuous Method for initial rate
∇ with the catalysis taking place, measure or calculate the Rx rate within the linear period
Discontinuous method for initial rate
∇ Endpoint method ∇ Stop the reaction ∇ After the catalysis takes place for some time, some chemicals such as acids, alkali, inhibitors are added to stop the reaction ∇ The reaction rate can be calculated Rx = D(P)/D(t)
Advantages of using continuous method
• Easy to find the linear range • Enzyme is active • Can finish in a short time
Advantages of using discontinuous method
Cheap equipment Easy to perform
Disadvantages of using continuous method
Equipment is expensive Needs good experiments skills
Disadvantages of using discontinuous method
• Maybe beyond the linear range • Enzyme is denatured or inhibited • Time consuming
In the lab I we used the _______ method to determine the activity of peroxidase
continuous
What are the factors that can affect enzyme catalysis?
o Temperature o PH. o Enzyme concentration o Substrate concentration o Activator o Ions or ionic strength o Solvents
How does an increase in substrate affect the rate of the reaction?
∇ In general, increase of substrate concentration the catalysis will increase up to a certain point until the enzyme is saturated.
What is Km (Michealis-Menton constant)?
it is the affinity of E to S Lower Km means higher affinity The Km or Michaelis constant is the substrate concentration at which v = Vmax/2 and its usual unit is M.
True/False Lower Km means higher affinity
true