Chemical Reactions A chemical equation lists all the elements in the reactants and in the products they form – Must obey Conservation of Matter, Mass, & Energy Reactants  Products 6H 2 O + 6CO 2  C 6 H 12 O 6 + 6O 2 The 6 listed before water, carbon dioxide, and oxygen is a coefficient – Multiplies the entire compound The subscripts tell how many atoms there are of the element directly preceding it The  is the yield. It is the action word in a word problem (yields, forms, becomes, produces, …) If there is a D above the , the reaction requires an input of energy.

Enzymes & Regulation of Enzymes Catalysts speed up reactions by lowering the activation energy associated with reactions. In the following exergonic reaction, the overall energy change of the reaction is unchanged but the energy of activation(E A ) is greatly reduced. – products have less energy than reactants – enzymes are not used in the reactions but free to couple with new reactants – Energy is released as heat, light, sound, … If the reaction was reversed the energy would be absorbed!

Biological Enzymes Biological enzyme are specific for the substrate (reactant) that they couple with. substrates bind to the enzyme's active site(groove or fold) – the conformation (3D shape) of the enzyme and reactant must be an exact fit (lock & key) the reaction takes place while bound the product is released once the reaction is completed

Mechanisms of Enzyme Interactions Binding orients molecules so that their active sites are in the correct position for the reaction to take place – once bound the enzyme may stretch or bend bonds weakening them – may create a micro environment different than in the cytosol with acidic side chains the enzyme may actively participate forming brief covalent bonds with the substrate

Enzyme Regulation Most enzymes require activation (cofactors & coenzymes) and regulation (inhibitors) in order to operate properly in the body. Without regulation all the metabolic pathways would operates simultaneously leading to chaos. – Regulation strategies include: Changing conformation Temp, pH, presence of an inhibitor Occupation of active site by another molecule