Chapter 6 Biochemistry Lecture
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Biochemistry: A Short Course Second Edition
Tymoczko Berg Stryer
2013 W. H. Freeman and Company
CHAPTER 6 Basic Concepts of Enzyme Action
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Outline
6.1 Enzymes Are Powerful and Highly Specic Catalysts
6.2 Many Enzymes Require Cofactors for AcDvity
6.3 Free Energy Is a Useful Thermodynamic FuncDon for Understanding Enzymes
6.4 Enzymes Facilitate the FormaDon of the TransiDon State
CHAPTER 6 Basic Concepts of Enzyme Action
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Enzymes
have
specific
substrates:
trypsin
K or R^
thrombin
LVPR^GS
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1. Oxidoreductase catalyze oxida4on-reduc4on reac4ons.
2. Transferases move func4onal groups between molecules.
3. Hydrolyases cleave bonds with the addi4on of water.
4. Lyases remove atoms to form double bonds or add atoms to double bonds.
5. Isomerases move func4onal groups within a molecule.
6. Ligases join two molecules at the expense of ATP.
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For the reac4on:
The free energy change is given by:
Where Go is the standard free energy, R is the gas constant, T is 298 kelvins, and the brackets denote concentra4on in moles.
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Enzymes accelerate the reaction rate, but will not alter the reaction equilibrium 10
Enzymes accelerate reactions by decreasing
G, the free energy of activation.
Enzymes cannot alter this Grxn
ac4va4on energy
Can enzymes make a non-spontaneous rxn occur?
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Enzymes bring substrates together to form an enzyme-substrate complex on a par4cular region of the enzyme called the ac4ve site.
The interac4on of the enzyme and substrates at the ac4ve site promotes the forma4on of the transi4on state.
Active sites may include distant residues
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1. The ac4ve site is a three-dimensional cleV or crevice created by amino acids from dierent parts of the primary structure.
2. The ac4ve site cons4tutes a small por4on of the enzyme volume. 3. Ac4ve sites create unique microenvironments. 4. The interac4on of the enzyme and substrate at the ac4ve site involves
mul4ple weak interac4ons. 5. Enzyme specicity depends on the molecular architecture at the ac4ve
site.
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Lock-and-key model
Induced-fit model
Two models of enzymesubstrate binding:
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proline racemase
inhibitor
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