Biochemistry: A Short Course - Chapter 5: Basic Concepts of Enzyme Action - Prof. Yogaraja, Study notes of Biochemistry

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• (^) Biochemistry: A Short Course
  • (^) First Edition
• (^) Biochemistry: A Short Course
• (^) First Edition Tymoczko • Berg • Stryer © 2010 W. H. Freeman and Company

CHAPTER 5

Basic Concepts of Enzyme Action

Enzymes

Enzymes are powerful and highly specific catalysts Accelerate reaction Most reactions in biological systems do not take place in the absence of enzymes

Carbonic anhydrase – fastest enzymes known It adding water to carbondioxide – simple reaction Transfer of corbon dioxide from the tissues to the blood They are highly specific Catalyzes a single reaction or a set of closely related reaction

carboxyl side of lysine and arginine residues Thrombin- catalyzes the hydrolysis of Arg-Gly bonds

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.

Co factor- two groups

1. Small organic molecules – called coenzymes

2. metals

Free energy is useful thermodynamic function for understanding enzymes Thermodynamic properties of a reaction depends on

1. The free energy difference between the products and- reactants-This determine whether the reaction will take place
2. The free energy required to initiate the conversation of reactants in to products - Determine the rate of reaction G = negative reaction take place spontaneously G = positive – reaction cannot take place- input of free energy is required- these reactions are called endergonic G = zero- equilibrium G = provides no information about the rate of reaction

Read page 69

Enzymes decreases the activation energy

The difference in free energy between the transition

state and the substrate is called the free energy of

activation or simply the activation energy

The formation of an enzyme substrate complex is the

first step in enzymatic catalysis. Enzymes bring together

substrates in enzyme substrate complexes. The

substrates are bound to a specific region of enzyme

called the active site.

Active site is composed of residues that come from

different parts of the polypeptide chain

1.The active site takes up a small part of the total volume of an enzyme.

2. Unique microenvironment
3. Substrate are bound to enzymes by multiple weak attractions
4. The specificity of binding depends on the precisely defined arrangement of atoms in an active site- lock and key and induced fit

The active site of the unbound enzyme is complementary in shape to the substrate – lock and key