Enzymes & Chemical Reactions

USES

But how do they work?

Background: Energy in Biochemical Rxns Endothermic reactions: energy is absorbed Product Energy Time Energy stored Reactant

Energy in Biochemical Rxns Exothermic reactions: energy is released What’s this? Product Energy Time Energy released Reactant

Activation Energy Energy required to make or break chemical bonds. Even exothermic reactions have activation energy. Energy Time Activation energy

Enzymes Are protein catalysts. Because they lower the amount of activation energy, they increase rate of reaction. Are not consumed in reactions. Cannot make reactions happen that wouldn’t happen normally. Most enzymes can only work on 1 reactant

How? Watch how the enzyme works: Allosteric Site

The Catalytic Cycle! The substrate (reactant) enters the active site The enzyme snuggles up to the substrate (called Induced Fit) The enzyme-substrate complex bends (using energy) and breaks the substrate The product is released and the enzyme prepares for the next substrate

Enzyme function Enzyme may put two molecules together (Anabolic cycle):

Types of Enzymes Kinase: Adds or removes phosphate groups, often from ATP Hydrase (or hydrolase): Adds or removes water. Isomerase: Changes the shape of molecules. Oxidoreductase: Performs redox reactions. Lyase: Breaks C-C bonds. Ligase: Makes C-C bonds.

Factors Affecting Enzymes pH and Temperature Enzymes function best within a small range Denaturation (unfolding of protein) occurs outside optimal range – protein no longer functions Inhibitors Certain molecules that can slow or stop enzyme function

Enzyme Inhibitors 2 Types: Competitive: Inhibitor molecule has a similar shape to the substrate, so they compete for the active site: Slows enzyme Non-competitive: Inhibitor fits into allosteric site & changes the shape of the active site: Stops enzyme May not be permanent

Enzymes don’t always act alone! Metabolic Pathway: A series of enzymes that work together to form an end product. The product of the 1st enzyme acts as the substrate for the 2nd enzyme… Example: Photosynthesis: More than 10 enzymes work together in series to create sugar!

All together now… Feedback Inhibition: A whole metabolic pathway can be inhibited by a single molecule! Usually the end product acts as a noncompetitive inhibitor to the first enzyme in the pathway Saves energy by limiting the amount of product