Enzymes Biological Catalysts Proteins that change the rate of cellular reactions without being consumed in the reaction

What happens in a chemical reaction? Bonds are broken Bonds are broken New bonds are formed New bonds are formed

Energy Investment in a Reaction Reactants must absorb energy from their surroundings for their bonds to break Reactants must absorb energy from their surroundings for their bonds to break Products release energy when their new bonds are formed Products release energy when their new bonds are formed The initial investment of energy for starting a reaction is ACTIVATION ENERGY, E A The initial investment of energy for starting a reaction is ACTIVATION ENERGY, E A

The reaction is Exergonic if the new bonds release more energy than was invested in the breaking of bonds Exergonic if the new bonds release more energy than was invested in the breaking of bonds Endergonic if the new bonds release less energy than was invested in the breaking of bonds Endergonic if the new bonds release less energy than was invested in the breaking of bonds

Why do molecules such as proteins, DNA, and other molecules that are in the cell which are free in energy and have the potential to decompose simultaneously not breakdown continually?

ANSWER: The activation energy for these reactions is too high at cellular temperatures.

BIG IDEA!!!!!! Enzymes speed chemical reactions by lowering the activation energy barrier Enzymes speed chemical reactions by lowering the activation energy barrier

Enzymes cannot Change ΔG Change ΔG Make an endergonic reaction exergonic Make an endergonic reaction exergonic They can only HASTEN REACTIONS THAT WOULD OCCUR ANYWAY! They can only HASTEN REACTIONS THAT WOULD OCCUR ANYWAY!

Enzymes are substrate specific Substrate—the reactant an enzyme acts on. Substrate—the reactant an enzyme acts on. The substrate “fits” the reactant(s) and hastens the move to product The substrate “fits” the reactant(s) and hastens the move to product Enzymes distinguish related compounds, even isomers Enzymes distinguish related compounds, even isomers An enzyme’s specificity is a function of its shape An enzyme’s specificity is a function of its shape

Only a region of enzyme binds to the substrate This region is called the ACTIVE SITE This region is called the ACTIVE SITE It is a groove on the surface of the protein It is a groove on the surface of the protein The shape of the enzyme at the active site matches the shape of the substrate The shape of the enzyme at the active site matches the shape of the substrate This area is not rigid, the enzyme changes its shape slightly to increase the fit. This is called INDUCED FIT This area is not rigid, the enzyme changes its shape slightly to increase the fit. This is called INDUCED FIT

Active Site

How do enzymes lower activation energy? Providing a template for the substrates to come together in the proper orientation Providing a template for the substrates to come together in the proper orientation Stressing the substrate molecules, stretching & bending critical chemical bonds Stressing the substrate molecules, stretching & bending critical chemical bonds Providing an environment that is conducive to a particular type of reaction Providing an environment that is conducive to a particular type of reaction

What factors affect enzyme activity? The concentration of the substrate The concentration of the substrate The concentration of the enzyme The concentration of the enzyme Temperature Temperature pH pH

What factors affect enzyme activity? Cofactors—nonprotein helpers usually bound to the active site. Examples include metal ions and coenzymes (vitamins) Cofactors—nonprotein helpers usually bound to the active site. Examples include metal ions and coenzymes (vitamins) Competitive inhibitors—Chemicals that resemble the normal substrate molecule & compete for admission to the active site. Competitive inhibitors—Chemicals that resemble the normal substrate molecule & compete for admission to the active site. Noncompetitive inhibitors—Bind to enzyme away from active site & change protein configuration Noncompetitive inhibitors—Bind to enzyme away from active site & change protein configuration

The Control of Metabolism Cellular metabolism is regulated by controlling when and where the cell’s various enzymes are active Cellular metabolism is regulated by controlling when and where the cell’s various enzymes are active Regulatory molecules bind to ALLOSTERIC SITES—a specific receptor site on the enzyme away from the active site Regulatory molecules bind to ALLOSTERIC SITES—a specific receptor site on the enzyme away from the active site

Allosteric Regulation Allosterically regulated enzymes are constructed from one more subunits Allosterically regulated enzymes are constructed from one more subunits Each subunit has its own active site with allosteric sites Each subunit has its own active site with allosteric sites

Feedback Inhibition The switching off of a metabolic pathway by its end product—which acts as an inhibitor The switching off of a metabolic pathway by its end product—which acts as an inhibitor