Enzymes Power Point Part 1 %28WebCT%29

8/7/2019 Enzymes Power Point Part 1 %28WebCT%29

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1. Introduction2. Cofactor3. Specificity of Enzyme

4. Naming / Nomenclature5. Classification of Enzyme6. Enzyme Kinetic & Michaelis-

Menten equation7. Factor affect enzyme activity


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Majority biochemical reaction cant take place spontaneously

Enzyme - Introduction


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Metabolism is usually divided into two

categories: Catabolism breaks down organic matter, for

example to get energy in cellular respiration. Anabolism uses energy to construct

components of cells such as proteins and

nucleic acids.


Biochemical reaction
http://en.wikipedia.org/wiki/Catabolismhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Anabolismhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Nucleic_acidhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Anabolismhttp://en.wikipedia.org/wiki/Cellular_respirationhttp://en.wikipedia.org/wiki/Catabolism


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Chemical reaction Using catalyst rate (acceleration) of chemical

reaction Catalyst - remain unchanges


Majority biochemical reaction cant take place spontaneously


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What is enzyme? In biochemical reaction Catalyst enzymesExample: Oxidation of fatty acid

Break down of protein



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Oxidation of fatty acid

The oxidation of a fatty acid to carbon dioxide andwater is not a gentle process in a test tube -

extremes of pH, high temperatures and corrosivechemicals are required.

Yet in the body, such a reaction takes placesmoothly and rapidly within a narrow range of pH

and temperature.



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Break down of protein

In the laboratory, the average protein mustbe boiled for about 24 hours in a 20% HCl

solution to achieve a complete breakdown.

In the body, the breakdown takes place infour hours or less under conditions of mild

physiological temperature and pH.



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Enzymes: Protein in nature High molecular weight

~ 10,000 to 2,000,000 Chain of amino acid Linked by peptide bond Denature at high temperature

Precipitated with salts / solvent

Enzyme Chemical Nature


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Enzyme

posses catalytic activity

rate of chemical reactionNo changes in the reactionRegenerate afterward

Enzyme Chemical Nature


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Cell metabolism required:

1. Extracting matter & energy from

the environment2. transporting various chemicals3. synthesizing new biomolecules

4. moving within its environment5. replicating, new generation


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Without enzymes very slowly or no reaction enzymes speed up reactions

maintain their life each reaction within cell catalyzed by a specific enzyme


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Enzymes - Protein in nature

3o structure

Folding rule Polar out / Non-polar InBonding

1. Hydrophobic interaction2. H-bond3. Ion pair (salt bridges)

4. Disulfide bonds


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What is substrate?

In enzymatic reaction

Substrate beginning of the process

Within substrate make / break chemical bonds


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Enzyme active site

Polypeptide chain folded unique 3-D shape pocket or cleft on the enzyme

surface active site


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substrate binds to the active site ofthe enzyme

form an Enzyme-Substrate complex

(ES complex) further reactions & form product then regenerated enzyme


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enzyme molecule lock Substrate key, active site keyhole of the lock.

This description is called the lock-and - key theory of enzymestructure.


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Some enzymes-Required NO chemical groups foractivity

Some enzymes- Require additional chemicalcomponent

- addition component Cofactor


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Three types of cofactors

Nature: organic or inorganic

Cofactor:**Non Protein chemical component**


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1.Coenzymecofactor enzyme loosely bound

Non-protein organic substanceAs carriers for transferring chemicalgroups or atoms from one enzyme toanotherMany coenzymes are derived fromvitamins


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1.Coenzyme

Example:

Nicotinamine adenine dinucledtide (NAD)acts as a coenzyme to dehydrogenase(the enzyme)by acting as a hydrogenacceptor


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2.Prosthetic groupcofactor enzymetightly bound

covalent bond

Non-protein organic molecules


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2.Prosthetic group

Example:

Haem is a prosthetic group.It is a ring-shaped organic molecule withiron at its centre.Haem is the prosthetic group of theelectron carrier cytochrome and of the enzyme catalase.


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Three types of cofactorsNature: organic or organic

3.Metal ions / inorganic ionsvarious metal ione.g. Mg+2, Mn+2, Zn+2, Cu+2

enzyme metalloenzymes


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3.Metal ions / inorganic ions

Example:Salivary amylaserequires thepresence of chloride (Cl-) ions beforeit will efficiently change starch intomaltose


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Apoenzyme an enzyme requires cofactor but does not have bound

Inactive enzyme

Holoenzyme

an apoenzyme + cofactor catalytically active


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Active site (key hole)

Specific 3 dimensional shape

Only one type of substrate

Specificity


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Few enzymesabsolute specificityCatalyze only one particular reaction

Other enzymesSpecificity for particular chemical

bond / functional group


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4 main classes of specificity :

1.Absolute specificity

2.Group specificity

3.Linkage specificity

4.Stereospecificity


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Enzyme only catalyse on onereaction

Example1. succinate dehydrogenase, that is specific for

succinate (In citric acid cycle / Krebs cycle)

1. Absolute specificity


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enzyme act on substrate which substrate with specific functional groups

ExamplePhosphatases

phosphate functional group


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enzyme only act on substrate which substrate having particular type of chemical bond /

linkage

Example

Esterases - hydrolysis of esters


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enzyme only act on substrate which substrate having steric / optical isomer

Example: Enzyme can discriminate between D-

stereoisomers and L-stereoisomers Catalyse the reaction on one of them


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Example: (a) & (b) are stereoisomer


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How polypeptide chain folds &make the active site


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1. -ve charged amino acid enzymeve charged substrate +ve charged Electrostatic interaction

e.g. aspartic acid & glutamic acid


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2. +ve charged amino acid Enzyme +ve charged Substrate -ve charged Electrostatic interaction E.g. histidine, lysine and arginine


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4. Hydrophilic amino acid Enzymehydrophilic Substratehydrophilic Hydrogen bonding


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Simple naming system

1. According to substrate that the

enzyme acted on Added suffix -ase

For example, Enzyme acted on substrate - arginine

called arginase


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Simple naming system

2. According to the type of reaction

catalyzed Added suffix -ase

For example, Enzyme glucose oxidase catalyzes

oxidation of glucose


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Systematize naming enzyme

International Enzyme Commission

IEC

based on type of catalytic reaction

6 major categories


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1. Oxidoreductases catalyze oxidation-

reduction reactionsExample:

Oxidoreductases - require a cofactor

NAD+, which accepts the hydrogens released during oxidation.


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1. Oxidoreductases catalyze oxidation-

reduction reactionsExample:

Oxidases - oxygen is used as an acceptor

glucose oxidase, glucose gluconic acid


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2. Transferases catalyze - transfer

functional groups of substrateExample:methyltransferase, transfers a methyl group


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2. Transferases catalyze - transfer

functional groups of substrateExample:transaminase, transferring an amino functional group from one

molecule to another. This allows for the interconversion of certainamino acids, and also allows amino acids to enter into glucosemetabolism.


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3.Hydrolases catalyzeaddition of a water moleculeprocess called hydrationcleaves the bond

Example:

Lipases, phosphatases,acetylcholinesterase and proteases


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4. Lyases catalyze removal of various groups from substrates

forming double bonds cleavage of C-C, C-O and C-N bonds not by means of hydrolysis


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5. Isomerases catalyze intramolecular rearrangements E.g. interconversion of D &L-isomeric


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6. Ligases catalyze the formation ofchemical bonds.

E.g. C-C, C-S, C-O and C-N bond

need input of chemical energy, ATPto form new bond


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Enzymes Power Point Part 1 %28WebCT%29