Download MBBS Biochemistry PPT 10 Enzymes Introduction And Mechanism Lecture Notes

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Action

Learning Objectives

Characteristics of Enzymes

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Classification of Enzymes

Nomenclature of Enzymes

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Active site and Transition state

Mechanism of enzyme actions
Clinical Importance

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Diagnosis and prognosis of diseases.

Disorders: genetic, nutritional, tissue damage

Pharmacologic agents and Gene Therapy

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Drugs /Antibiotics.

Enzymes

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Enzymes are specialized proteins that function in

the acceleration of chemical reactions

Exception?

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Ribozymes
Characteristics of enzyme catalysts

Increase rate of reaction by factor of 106

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Highly selective and specific

Not changed as a result of catalysis

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Does not change the equilibrium constant

Enzymes Alter Only the Reaction Rate

and Not the Reaction Equilibrium

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Cofactor containing enzymes
Examples of coenzymes and cofactors

Vitamin

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Coenzyme

Enzymes

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Enzymes

Cofactors

Thiamine

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TPP

Transketolase,

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Ferroxidase

Copper

pyruvate

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Dehydrogenase

Riboflavin

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FAD, FMN

Succinate

Carbonic anhydrase

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Zinc

dehydrogenase

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Niacin

NAD,NADP

Malate

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Cytochrome oxidase

Copper,

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dehydrogenase

Iron

Pyridoxine

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PLP

transaminases

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Hexokinase

Magnesium

Folic acid

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THF

One carbon

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Glutathione peroxidase

Selenium

metabolism

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Pantothenic acid

Coenzyme A Pyruvate

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Arginase

Manganese

dehydrogenase

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Xanthine Oxidase

Molybeden

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Classification of Enzymes
Nomenclature of Enzymes

International Union of Biochemistry and Molecular

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Biology (IUBMB)

Recommended name

Systematic name EC1.1.1.27 (Lactate

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Dehydrogenase)

Special names

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Phosphatase vs Phosphorylase

Synthetase vs Synthase

Dehydrogenase vs Oxidase vs Oxygenase

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Active site

Active

Site

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Binding

Catalytic

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site

site

Features of Active Site

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3D cleft formed by groups that come from different

parts of the amino acid sequence

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takes up a relatively small part of the total volume

of an enzyme

clefts or crevices

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Substrates are bound to enzymes by multiple weak

attractions
Transition state

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Enzymes lower activation energy by stabilizing

transition state

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The active site can provide catalytic groups that

enhance the probability that the transition state

is formed

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1. LOCK-AND-KEY MODEL FOR SUBSTRATE BINDING: Emil

Fisher

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2. "INDUCED FIT" MODEL FOR SUBSTRATE BINDING: Daniel E

koshland
Mechanism of catalysis

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1. Catalysis by Proximity
2. Catalysis by strain

Chymotrypsin

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3. Acid Base Catalysis
4.Covalent Catalysis
5. Metal ion catalysis

Metal ion catalysis

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Assist in binding of the substrate,

Stabilize developing anions in the reaction.

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Accept and donate electrons in oxidation-

reduction reactions.
Serine protease like chymotrypsin : acid base

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catalysis as well as covalent catalysis

RNAase : covalent catalysis

Metal ion: carbonic anhydrase

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Clinical scenario 1

Vitamin B6 responsive and unresponsive

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cystathionuria: two variant molecular forms
Clinical Scenario 2

A child was born with inherited mutation in an

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enzyme, so that it is unable to bind its coenzyme.

As a result,
(A) the enzyme doesnot bind to its subtrate
(B) the enzyme will not be able to form transition

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state complex
(C) the reaction will proceed with free coenzyme
(D) the enzyme will use some other coenzyme

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References

Victor W. Rodwell, David A. Bender, Kathleen M. Botham,

Peter J. Kennelly, P. Anthony Weil. Harper's Illustrated

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Biochemistry, 30th Edition

Denise R. Ferrier; Lippincott Illustrated Reviews

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Biochemistry, 7th Edition

Thank You!