Enzymes

1. Meng Li Sun-heeChoi Tanya Yemelianov Enzymes

2. Enzymes • Are biological molecules that increase the rate of chemical reactions in the cell. An enzyme acts as catalyst for specific chemical reactions, converting a specific set of reactants (called substrates) into specific products. Without enzymes, life as we know it would not exist.

3. Chemical Nature of Enzymes All known enzymes are proteins. They are high molecular weight compounds made up principally of chains of amino acids linked together by peptide bonds.

4. Enzymes – How do they work? • Enzymes work by binding to one or more specific molecules called reactants or substrates at the place called a binding site. This forms an enzyme-substrate complex. The interactions between the enzyme and substrates weakens some of the chemical bonds in the substrate making two substrates link, forming a new molecule. The product is then released from the active site and enzyme goes back to it’s original shape. Other enzymes bind to one substrate and form two substrates.

5. Enzymes – How do they work? Formation of two products from one substrate: http://en.wikipedia.org/wiki/Enzymes

6. Naming an Enzyme: • Except for some of the originally studied enzymes such as pepsin, rennin, and trypsin, most enzyme names end in "ase". Example: lactase, alcohol dehydrogenase, DNA polymerase. • The International Union of Biochemistry (I.U.B.) has proposed standards of enzyme classification which recommend that enzyme names indicate both the substrate acted upon and the type of reaction catalyzed.

7. Naming and Classification:

8. Naming and Classification:

9. EC-Enzyme Commission number • EC number is a numerical classification scheme for enzymes based on the reaction they catalyze. • EC number specifies a reaction and NOT a specific enzyme

10. Practical use of Enzymes: Enzymes are used in biological washing powders • The enzymes in biological washing powders will decompose stains easily Because stains are made of different types of molecules, a range of enzymes are needed to break them down. Proteasesbreak down proteins, so are good for blood, egg, gravy, and other protein stains. Amylases break down starches, andlipasesbreak down lipids.

11. Catalytic Efficency • A catalyst is a substance that speeds up the rate of a chemical reaction but is not itself changed by the reaction. • Enzymes are true catalysts that speed chemical reactions.

12. Energy levels • To speed chemical reactions by lowering activation energies.

13. Denaturing • Extreme temperature and PH can change enzyme shape, rendering it useless.

14. Factors Affecting Enzyme Activity • Enzyme Concentration • Substrate Concentration • Temperature • The Effect of PH

15. Rate of reaction of an enzyme reaction changes at different temperatures Optimum temperature Enzyme is denaturing Molecules gain kinetic energy Rate Of Reaction 0 10 20 30 40 50 60 70 Temperature/oC

16. The activity and shape of enzymes is also affected by pH • Enzymes prefer to work at an optimum pH. Outside of its pH range the enzyme is denatured. Optimum pH pepsin amylase Rate Of Reaction 1 2 3 4 5 6 7 8 9 10 11 12 pH

17. Specificity • One of the properties of enzymes that makes them so important as diagnostic and research tools is the specificity they exhibit relative to the reactions they catalyze. • A few enzymes exhibit absolute specificity; that is, they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group.

18. Absolute specificity • Enzyme that catalyze the reaction of one and only one substance. • Uricase, which act only on uric acid • Carbonic anhydrase, which acts only on carbonic acid • Lactase , which acts on lactose • Sucrase, which acts on sucrose • Maltase, which acts on maltose

19. Relative specificity • Enzyme that acts on substrates that are similar in structure and contain the same type of bonds. • Lipase that hydrolyzes lipids • Proteases split up proteins • Phosphates hydrolyze phosphate esters.

20. Enzyme part lists • Apoenzyme: The polypeptide or protein part of the enzyme is called the apoenzyme and may be inactive in its original synthesized structure. • The inactive form of the apoenzyme is known as a proenzyme or zymogen. • Cofactors: A cofactor is a non-protein substance which may be organic, and called a coenzyme. The coenzyme is often derived from a vitamins. • When the cofactor is an organic substance, it is a coenzyme. The cofactor may also be an inorganic ion (usually a metal cation, such as Mg2+, Zn2+, or Fe2+).

22. Enzyme Cofactors  The conversion of lactate to pyruvate is enzymatically catalyzed by lactate dehydrogenase. (LDH) • In this reaction lactate loses two electrons (becomes oxidized) and is converted to pyruvate. • NAD+ gains two electrons (is reduced) and is converted to NADH.

23. Lock and key model vs induced fit model

25. References • Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Central Role of Enzymes as Biological Catalysts. http://www.ncbi.nlm.nih.gov/books/NBK9921/ • http://www.worthington-biochem.com/introbiochem/Enzymes.pdf • http://www.biology-questions-and-answers.com/enzyme-activity.html • http://www.nuffieldfoundation.org/practical-biology/factors-affecting-enzyme-activity • http://www.biotechlearn.org.nz/themes/biotech_at_home/enzymes_in_washing_powders

26. References • Bennett, T. P., and Frieden, E.: Modern Topics in Biochemistry, pg. 43-45, Macmillan, London (1969) • Organic and Biochemistry for Today Spencer L. Seager / Michael R. Slabaugh, pg608-616, Mr. Kevin A. Boudreaux , Angelo StateUniversity www.angelo.edu/faculty/kboudrea • Apoenzyme and holoenzyme http://en.wikibooks.org/wiki/Structural_Biochemistry/Enzyme/Apoenzyme_and_Holoenzyme • http://academic.brooklyn.cuny.edu/biology/bio4fv/page/coup_ox.htm • http://www.elmhurst.edu/~chm/vchembook/570enzymes.html • Enzyme specificity http://osp.mans.edu.eg/medbiochem_mi/Cources/Biochemistry/1st_year_medicine/Enzymes/files/Lecture_02.pdf