Enzymes Part 1

1. Enzymes Part 1 M.F.Ullah, Ph.D Showket H.Bhat, PhD COURSE TITLE: BIOCHEMISTRY 1 COURSE CODE: BCHT 201 PLACEMENT/YEAR/LEVEL: 2nd Year/Level 4, 1st Semester

2. What Are Enzymes? • Enzymes are Proteins • Act as Catalyst to accelerates a reaction • Not permanently changed/destroyed in the process

3. Enzyme-Substrate Complex Enzyme The reactant on which the enzyme acts on is the substrate Joins Substrate

4. C. Classification of Enzymes 1) named and classified according to the substrate acted upon and the reaction catalyzed. 2) trivial names-- end in -ase -- urease, hexokinase. 3) named based on a formal systemic catalog (IUB) with six major classifications. (All enzymes should fall into one of these categories and all enzymes therefore have a formal name.)

5. Class 1. Oxidoreductases- catalyze redox processes Example: RCH2-OH  RCH=O Class 2. Transferases- transfer chemical groups from one molecule to another or to another part of the same molecule. O O Example: CH3-C-SCoA + XR CH3-C-XR + HSCoA acetylCoA acetyl group transferred

6. Class 3. Hydrolases- cleave a bond using water to produce two molecules from one. O H2O O example: --CNH-R  --C-OH + H2N-R cleavage of a peptide bond Class 4. Lyases- remove a group from or add a group to double bonds. H-X H X ---C=C---  ---C--C---

7. Class 5. Isomerases- interconvert isomeric structures by molecular rearrangements. CH3CH3 HC-OH HO-CH COOH COOH Class 6. Ligases -- join two separate molecules by the formation of a new chemical bond usually with energy supplied by the cleavage of an ATP. example: O ATP ADP+Pi O -OOC-C-CH3 + CO2-OOC-C-CH2-COO- pyruvateoxaloacetate enzyme = pyruvatecarboxylase

8. The substrate • The substrate of an enzyme are the reactants that are activated by the enzyme • Enzymes are specific to the substrates

9. Enzyme Active Site • A restricted regionof an enzyme molecule which binds to the substrate. Active Site Substrate

10. The Lock and Key model for enzyme-substrate interaction • 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

11. Active Site substrate Enzyme induced fit Induced Fit model for enzyme-substrate interaction • A change in the shape of an enzyme’s active site • Induced by the substrate.

12. The Induced Fit • Some enzymes can change theirshape (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 chemicalenvironmentsuitable for the reaction

13. Hexokinase (a) without (b) with glucose substrate The Induced Fit Hypothesis • This explains the enzymes thatcanreactwith a range of substrates of similar types

14. What Affects Enzyme Activity? • Three factors: 1. Environmental Conditions 2. Cofactors and Coenzymes 3. Enzyme Inhibitors

15. 1. Environmental Conditions 1. Extreme Temperature are the most dangerous - high temps may denature (unfold) the enzyme. • Optimum Temperature required • - For most enzymes the optimum temperature is about 30°C • - Most enzymes however are fully denatured at 70°C 2. Optimum pH (most like 6 - 8 pH near neutral) - Extreme pH levels will produce denaturation 3. Ionic concentration (salt ions)

16. 2. Cofactors and Coenzymes • 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

17. Vitamins are precursors of cofactors