Enzymes!

Enzymes and metabolism Metabolism requires chemical reactions  Exothermic (where reactants have more stored energy than products) release energy  Endothermic (where reactants have less stored energy than products) absorb energy

Both kinds of reactions require activation energy (to start going) The more readily the reactants react, the smaller the activation energy (Ea)

The easiest way to get a reaction to happen is to add heat In the human body this is not possible The solution is to use biological catalysts or enzymes Enzymes are protein molecules which speed up the rates of biochemical reactions, without being altered by the reaction. They lower the activation energy of a reaction

Each enzyme catalyzes one specific reaction (breaking things apart, putting things together or passing electrons along) This is because each enzyme has an “active site” (the part of the enzyme that holds the substrate in place and allows the reaction to occur Substrates bind to an enzyme's active site in a “lock and Key” manner

Each enzyme has a very specific shape New model called the “INDUCED FIT” model Similar to “lock and key” model, but suggests that there is a slight change in the shape of the complex Video (wooooooo)

Metabolic processes have many steps Each step requires a specific enzyme If any enzyme is missing the whole pathway is shut down

Co enzymes and Cofactors Help binding of enzymes to substrates  Cofactors: inorganic  Coenzymes: organic, synthesized for vitamins

Coenzymes

Factors that affect Enzyme reaction rates Temperature:  Higher temp, faster reaction rate (more energy means more collisions) Reaction rates peak at 37 ° C (body temp) Above this temp enzymes begin to denature, which changes the acitve site Greater the change in the active site, less effective the enzyme No enzyme = very slow reaction

That is why high fevers are dangerous!!

PH:  Certain enzymes function best with certain pH's (pg 595 fig 23.11)  Therefore, enzymes in stomach only function in stomach

Mode action of pH:  Folds in secondary proteins caused by H bonds between acid and amino groups  H and OH ions will affect these bonds  Changes the shape of the enzyme  Therefore active site is changed, affecting enzymes ability to assist reactions

Concentration:  More substrate molecules means more collisions therefore higher rate of reaction  Only works for enzyme catalyzed reactions up to a point....then reaction rate levels off due to limited enzyme quantities (see fig pg 597)  However, if you add more enzyme at this point you increase the reaction rate again