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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
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
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