Enzymes
Concept: Every reaction that takes
place in a cell is catalyzed by an enzyme. With few exceptions, enzymes
are proteins.
- catalysts: a molecule that speeds up or slows down a reaction but is not concumed by the reaction. It acts by lowering the activation energy (amount of energy it takes to get out of bed in the morning) of a reaction (going to class). [assuming their is an overall spontaneous desire to go to class.]
- Enzyme reaction can be divided into two phases:
- E (enzyme) + S (substrate) = [ES] complex = E + P (product)
- Binding (recognition): This is the phase in which discrimination occurs. Enzymes can be highly selective in the binding of reactants (substrates).
- They can discriminate very small structural differences.
- They bind through non-covalent interactions.
- Strength of binding can be determined by the number of interactions between substrate and enzyme.
- Binding dicrimination is never all-or-none.
- Catalysis (conversion of the bound reactant to product): This phase generally involves a small number of amino acid side chains in the activesite of the enzyme (protein)
- Both phases take place at a limited site on the protein referred to as the active site
- The velocity of an enzyme catalyzed reaction is dependent on the substrate concentration. (figure 6-21b). At high concentrations of substrate, the velocity approaches a maximum (Vmax). Most cellular concentrations of substrates are at concentrations well below Vmax.
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