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 23.12 pg 597)

However, if you add more enzyme at this point you increase the reaction rate again