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catalytic macromolecules that change the rate of the reaction without being permanently changed in the process.

transition state

unstable condition of reactant molecules that have absorbed sufficient free energy to react

How do enzymes change the rate of reaction

they lower the activation energy which is the amount of energy that reactant molecuyles must absorb to start a reaction.

How spe3cific are enzymes

they are substrate specific and that specificity depends upon the enzymes three dimensional shape


the substance the enzyme acts on and makes more reactive. binds to the enzymes active site

active site `

restricted region of an enzyme molecule which binds to the substrate. usually a pocket on the proteins surface. changes shape in response to the substrate. it is an enzymes catalytic center

induce fit

change in the shape of an enzymes active site

steps in catalytic cycle

1. substrate binds to active site forming an enzyme substrate complex. Substrate is held in active site by weak interactions 2) induce fit of active site around the subtrate catalyzes the conversion of the substrate to the product 3) product departs active site and the enzyme emerges in its origninal form

how do enzymes lower activation energy

In reactions with two or more reactants, the active site provides a template for the substrates to come together in the proper orientation for a reaction to occur between them.
As the active site clutches the substrates with induced fit, the enzyme may stress the substrate molecules, stretching and bending critical chemical bonds that must be broken during the reaction.

Effects of temp

optimal temp allows the greatest number of molecular collision to occur without denaturing the enzyme. enzyme reaction rate increases with increasing temp. beyond optimal tempreaction rate slows because of denaturing.

optimal temp for human enzymes

35-40 C

optimal pH for human enzymes



nonprotein helpers that bind tightly to the active site that help in catalytic activity. two types : inorganic (metal atoms) and organic (vitamins)

competitive inhibition

reduce the productivity of enzymes by blocking substrates from entering active sites

noncompetitve inhibotors

do not directly compete with the substrate for the active site, but bind to another part of the enzyme causing it to change shape.

allosteric regulation

Regulatory molecules bind to the allosteric site resulting in changing the enzyme's
shape and therefore function.
-allosteric sites are usually located where subunits are joined
-weak attachments

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