HOW DO ENZYMES ACHIEVE SPECIFISITY ?

1. HOW DO ENZYMES ACHIEVE SPECIFISITY? By Stella Angeli Background taken from: http://www.bioage.com/images/enzymes.jpg

2. ENZYMES • DEFINITION Efficient catalysts which speed up biochemical reactions by providing an alternative reaction pathway of lower activation energy. • IMPORTANT CHARACTERISTICS • Remain unchanged at the end of a chemical reaction • They do not change the products after the reaction • Highly selective, catalysing specific reactions • Speed up the same chemical reaction going in opposite directions • Nearly all known enzymes are proteins http://student.biology.arizona.edu/honors2003/group15/Pictures/Enzymes1.jpg

3. Mechanism of Enzyme Action • The whole process begins with the binding of the substrate to the active site of the enzyme. The active site is the specific region of the enzyme which combines with the substrate. • changes in the distribution of electrons in the chemical bonds of the substrate • reactions that lead to the formation of products • The products are released and the enzyme is ready to catalyze another reaction. http://en.wikipedia.org/wiki/Enzyme

4. Factors affecting catalytic activity of enzymes • pH • Temperature http://www.rsc.org/education/teachers/learnnet/cfb/enzymes.htm http://www.rsc.org/education/teachers/learnnet/cfb/enzymes.htm • Concentration of enzyme and substrate Both pictures taken from:http://www.rsc.org/education/teachers/learnnet/cfb/enzymes.htm

5. Lock and Key analogy • Lock and Key theory was first postulated in 1894 by Emil Fischer and explains the specific action of an enzyme. • LOCK = enzyme • KEY = substrate • The substrate molecule must have a matching shape that will fit into the active site. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme). http://www.elmhurst.edu/~chm/vchembook/571lockkey.html

6. Enzymes specificity • Specificity of an enzyme depends on its own shape,charge and hydrophobic/hydrophiliccharacteristics of the enzyme. • The active site has a unique geometric shape that is complementary to the geometric shape of a substrate molecule. This means that enzymes specifically react with only one or a very few similar molecules. • A few enzymes have absolute specificity they will catalyze only one particular reaction. Other enzymes will be specific for a particular type of chemical bond or functional group. • There are four distinct types of specificity: • Absolute specificity - the enzyme will catalyze only one reaction. • Group specificity - the enzyme will act only on molecules that have specific functional groups, such as amino, phosphate and methyl groups. • Linkage specificity - the enzyme will act on a specific type of chemical bond without using the other parts of the molecular structure. • Stereochemical specificity - the enzyme will act on a particular steric or optical isomer. Background taken from: http://peds.oxfordjournals.org/content/vol19/issue11/images/medium/coverfig.gif

7. Enzyme Inhibitors-influence specificity • Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner, by influencing its specificity. There is a variety of types of inhibitors including: • Physical or chemical changes which ultimately denatures the protein portion of the enzyme. (e.g. Heavy metals, antibiotics etc.) IRREVERSIBLE REVERSIBLE Non-competitive Competitive

8. Competitive inhibitors • A competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate. • The inhibitor competes for the same active site as the substrate molecule. • It may interact with the enzyme at the active site, but no reaction takes place. • It is "stuck" on the enzyme and prevents any substrate molecules from reacting with the enzyme. http://porpax.bio.miami.edu/~cmallery/255/255enz/competitive_inhibition.jpg

9. Non-competitive inhibitors • A non-competitive inhibitor is a substance that interacts with the enzyme, but usually not at the active site.   • The non-competitive inhibitor reacts either remote from or very close to the active site.   Change to the shape of the enzyme and thus to the active site, so that the substrate can no longer interact with the enzyme to give a reaction. http://www.uic.edu/classes/bios/bios100/mike/spring2003/noncompinhibit.jpg

10. Summary • Enzymes are efficient catalysts which speed up biochemical reactions. • Specificity of an enzyme depends on its own shape, charge and hydrophobic/hydrophilic characteristics of the enzyme. • Geometric shape of the active side is complementary to the geometric shape of a substrate. • Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner and influence its specificity. -IRREVERSIBLE -REVERSIBLE COMPETITIVE NON-COMPETITIVE

11. References • Stryer L., Biochemistry book, 4th edition, 1995 • http://www.rsc.org/education/teachers/learnnet/cfb/enzymes.htm • http://www.elmhurst.edu/~chm/vchembook/571lockkey.html • http://www.worthington-biochem.com/introBiochem/specificity.html • http://www.purchon.com/biology/enzymes.htm • http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEnzym.html • http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEnzym.html • http://en.wikipedia.org/wiki/Enzyme