EnzymesPart 1

COURSE TITLE: BIOCHEMISTRY 1COURSE CODE: BCHT 201

PLACEMENT/YEAR/LEVEL: 2nd Year/Level 4, 1st Semester

M.F.Ullah, Ph.DShowket H.Bhat, PhD

Enzymes are ProteinsProteins

Act as CatalystCatalyst to accelerates a reaction

Not permanentlyNot permanently changed/destroyed in the process

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The reactant on which the enzymeenzyme acts on is the substratesubstrate

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EnzymeSubstrate Joins

C. Classification of EnzymesC. Classification of Enzymes

1) named and classified according to thesubstrate acted upon and the reactioncatalyzed.2) trivial names-- end in -ase -- urease,hexokinase.3) named based on a formal systemiccatalog (IUB) with six major classifications.(All enzymes should fall into one of thesecategories and all enzymes therefore havea formal name.)

Class 1. OxidoreductasesOxidoreductases- catalyze redoxprocesses

Example: RCH2-OH RCH=O Class 2. TransferasesTransferases- transfer chemical groupsfrom one molecule to another or to another partof the same molecule. O OExample: CH3-C-SCoA + XR CH3-C-XR + HSCoA acetyl CoA acetyl group transferred

Class 3. HydrolasesHydrolases- cleave a bond using waterto produce two molecules from one.

O H2O O example: --CNH-R --C-OH + H2N-R cleavage of a peptide bond

Class 4. LyasesLyases- remove a group from or add agroup to double bonds.

H-X H X ---C=C--- ---C--C---

Class 5. IsomerasesIsomerases- interconvert isomericstructures by molecular rearrangements. CH3 CH3

HC-OH HO-CH COOH COOH

Class 6. LigasesLigases -- join two separate moleculesby the formation of a new chemical bond usuallywith energy supplied by the cleavage of an ATP.example: O ATP ADP+Pi O-OOC-C-CH3 + CO2 -OOC-C-CH2-COO-

pyruvate oxaloacetate enzyme = pyruvate carboxylase

The substrate of an enzyme are the reactants that are activated by the enzyme

Enzymes are specific to the substrates

A restricted regionrestricted region of an enzymeenzyme molecule which bindsbinds to the substratesubstrate.

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EnzymeSubstrate

Active Site

Fit between the substrate and the active site of the enzyme is exact

Like a key fits into a lock very precisely The key is similar to the enzyme and the substrate

is similar to the lock. Temporary structure called the enzyme-substrate

complex formed Products have a different shape from the substrate Once formed, they are released from the active

site Leaving it free to become attached to another

substrate

A changechange in the shapeshape of an enzyme’s active siteenzyme’s active site

InducedInduced by the substrate.substrate.

Enzyme

Active Sitesubstrate

induced fit

Some enzymes can change their shape (conformation)

When a substrate combines with an enzyme, it induces a change in the enzyme’s shape

The active site is then moulded into a exact conformation

Making the chemical environment suitable for the reaction

This explains the enzymes that can react with a range of substrates of similar types

Hexokinase (a) without (b) with glucose substrate

Three factors:Three factors:1.1. Environmental ConditionsEnvironmental Conditions

2.2. Cofactors and CoenzymesCofactors and Coenzymes

3.3. Enzyme InhibitorsEnzyme Inhibitors

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1. 1. Extreme Temperature are the most Extreme Temperature are the most dangerousdangerous- high temps - high temps may denature (unfold) denature (unfold) the enzyme.enzyme.

- Optimum Temperature requiredOptimum Temperature required- - - For most enzymes the optimum

temperature is about 30°C- - Most enzymes however are fully

denatured at 70°C2.2. Optimum pH (most like 6 - 8 pH near Optimum pH (most like 6 - 8 pH near neutral)neutral)

- - Extreme pH levels will produce denaturation3.3. Ionic concentration (salt ions)Ionic concentration (salt ions)

An additional non-protein molecule that is needed by some enzymes to help the reaction

Tightly bound cofactors are called prosthetic groups

Cofactors that are bound and released easily are called coenzymes

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