Enzymes Chapter 8 Section 8.2

Chemical Reactions Some reactions occur quite slowly There are a few options to speed it up Increase Temperature Problem: temperature would be so high that it would permanently coagulate (uncoil) the proteins in our bodies Ie) Fever – too high too long: disruptions to chemical reactions in body – can be fatal

Ways to Speed up Chemical Rxns Con’t Use a Catalyst A chemical that speeds up a chemical reaction without altering the products or being altered itself It speeds up the reaction by lowering the activation energy

Proteins As Catalysts Cells make specific proteins that act as catalysts. An ENZYME is a protein molecule that acts as a catalyst.

Perfect Fit… Each enzyme (a protein molecule that acts as a catalyst) has a specific 3-D shape that perfectly matches the reactant molecules it is supposed to combine with. Reactant molecule is called the SUBSTRATE. ACTIVE SITE – the area of an enzyme that combines with the substrate. http://www.youtube.com/watch?v=CZD5xsOKres&feature=related

Helping enzymes… Some enzymes require special molecules to help them bind to substrate molecules. There are two types of molecules that can do this: COFACTORS = inorganic ions that help an enzyme bind with a substrate COENZYMES = organic molecules, formed from vitamins, that help an enzyme bind with a substrate

Lock and Key Theory

Induced-Fit Model This model suggests that the actual shape of the active site is altered slightly when the substrate molecules are bonded, making the fit between the enzyme and substrate even tighter.

Things that Affect Enzymes at Work Temperature - Too low: bonds that determine the enzyme’s shape are not flexible enough to fit substrates properly - Too high: bonds too weak – molecular shape, structure, and other properties thus change (DENATURE)

Things That Affect Enzymes at Work pH Human enzymes work best ~ 6-8 Altering the pH will change the 3D shape of the protein

Things That Affect Enzymes at Work Substrate Molecule Concentration The greater the number of substrate molecules, the more likely a substrate is to bind, and the reaction rate increases. 13

Things That Affect Enzymes at Work Inhibitors Molecules that attach to the enzyme and lower its ability to bind with its substrate. 2 classes Competitive Non-competitive

Competitive Inhibitors Attach to ACTIVE SITE of enzyme. Compete with substrate to occupy active site when both competitive inhibitor and substrate are present. If there are many inhibitor molecules, it wins the active site and stops enzyme activity.

Non-Competitive Inhibitors Attach anywhere except the active site on the enzyme. This other site is known as the ALLOSTERIC SITE (regulatory site). Changes the 3D shape of enzyme, including the active site. If the active site shape is changed the substrate can no longer bind to the enzyme and enzyme activity is stopped. http://www.youtube.com/watch?v=PILzvT3spCQ

Regulation of Enzyme Activity Metabolic pathways are orderly sequences of chemical reactions, with enzymes regulating each step. Metabolic pathways can be turned on or off. They are turned off by feedback inhibition and turned on by precursor activity.

Feedback Inhibition The inhibition of an enzyme in a metabolic pathway by the final product of that pathways. The final product of the metabolic reaction binds to the regulatory site (allosteric site) and changes the shaped of the enzyme so that the substrate can no longer bind. This turns off the metabolic pathway. http://www.youtube.com/watch?v=rHDp4wJ1U0w&NR=1

Precursor Activity A build-up of the initial substrate can turn on a metabolic pathway. In precursor activity, an initial substrate molecule binds to the regulatory site (allosteric site) of the enzyme and changes the shape of the enzyme so that the substrate will bind with the enzyme. This turns on the metabolic pathway.