Biochemistry Lecture 9 PDF
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Mansoura University
Dr. El-Sawy
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This document contains lecture notes on Biochemistry, specifically focusing on enzymes. It details different types of enzymes, their classifications, and the mechanisms of enzyme action. The notes include diagrams and explanations, potentially suitable for an undergraduate level course.
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Biochemistry Enzymes LECTURE (9) DR. El-Sawy 1 Biochemistry Enzymes Org...
Biochemistry Enzymes LECTURE (9) DR. El-Sawy 1 Biochemistry Enzymes Organic thermo-labile catalysts. Def : A catalyst is a substance that accelerates chemical reaction without change (not consumed, not affect the end product). All enzymes protein in nature except Chemical nature : Ribozymes RNA in nature. Simple Protein enzymes: Formed of protein only. Complex (conjugated) Protein enzymes: Formed of : 1. Protein part: apo-enzyme. 2. Non- protein: cofactor (coenzyme or prosthetic group) The whole enzyme is called holoenzyme. Classification Coenzyme Prosthetic group Chemical nature Organic Inorganic Effect of heat Thermo-labile Thermo-stable Loosely bound Firmly bound to Binding to the enzyme to the enzyme the enzyme Vitamin B Metal ions as: Examples derivatives e.g: calcium (Ca) & NAD, FAD zinc (Zn). DR. El-Sawy 2 Biochemistry Enzymes Enzymes Vocabulary Substrate The reactant which binds to enzyme Product The end result of reaction Active Restricted region of enzyme molecule which binds to (catalytic substrate. site) Formed from a.a. sequences in polypeptide chain. Mechanism of enzyme action: 1. Substrate (S) binds to enzyme (E) activated intermediate enzyme substrate complex (ES) 2. The activated complex (ES) cleaved to products (P) & original enzyme (E). S + E → ES → E +P Enzymatic reaction steps: 1. Substrate approaches active site. 2. Enzyme-substrate complex forms. 3. Substrate transformed into products. 4. Products are released. 5. Enzyme is recycled. DR. El-Sawy 3 Biochemistry Enzymes Theories of enzyme substrate binding Lock and key theory Induced fit theory Proposed by fisher in 1894. Proposed by Koshland in 1958. Catalytic site of enzyme has a shape that is Catalytic site of enzyme is not complementary to complementary (fit) to shape of substrate. substrate. Substrate fits in this catalytic site as lock and key. It is a rigid model (fixed). It a flexible model. Binding of substrate to enzyme changes in shape of catalytic site making it more fit for substrate. DR. El-Sawy 4
