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Chapter 6

KIN217 Chapter Notes - Chapter 6: Cittern, Atp Hydrolysis, Paga

Course Code
Monica Vesely

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Chapter 6: Basic Concepts of Enzyme Action
Enzymes Are Powerful and Highly Specific Catalysts
-Enzymes accelerate reactions by factors of as much as a million or more
Proteolytic Enzymes Illustrate the Range of Enzyme Specificity
-Proteolytic enzymes differ in their degree of substrate specificity
-The specificity of an enzyme is due to the precise interaction of the substrate with the enzyme
-This precision is a result of the intricate three-dimensional structure of the enzyme protein
There Are Six Major Classes of Enzymes
oTransfer electrons between molecules
oCatalyze oxidation-reduction reactions
oTransfer functional groups between molecules
oCleaves molecules by the addition of water
oAdds atoms or functional groups within a molecule
oJoin two molecules at the expense of ATP hydrolysis
Many Enzymes Require Cofactors for Activity
-The precise role varies with the cofactor and the enzyme
-An enzyme without its cofactor is referred to as an apoenzyme
-The complete catalytically active enzyme is called a holoenzyme
-Cofactors can either be:
oSmall organic molecules, derived from vitamins, called coenzymes
-Tightly bound coenzymes are called prosthetic (helper) groups
-Loosely associated coenzymes are more like cosubstrates because, like substrates and products,
they bind to the enzyme and are released from it
-Coenzymes are different than normal substrates not only because they are derived from vitamins
but also because they are used by a variety of enzymes
-Different enzymes that use the same coenzyme usually carry out similar chemical transformations
Free Energy Is a Useful Thermodynamic Function for Understanding Enzymes
-Whether the reaction can take place at all depends on free-energy differences
-Free Energy (ΔG) is a thermodynamic property that is a measure of useful energy or energy that is
capable of doing work
-To understand how enzymes work, we need to consider:
oThe free energy difference, ΔG, between the products and the reactions
oThe free energy required to initiate the conversion of reactants into products
The Free-Energy Change Provides Additional Information About the Spontaneity but Not the Rate of a
-A reaction can take place spontaneously only if ΔG is negative (exergonic)
-A reaction cannot take place spontaneously id ΔG is positive (endergonic)
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