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Unformatted text preview: 0B X X X V V V I I I I I I . . . B B B i i i o o o l l l o o o g g g i i i c c c a a a l l l c c c a a a t t t a a a l l l y y y s s s i i i s s s : : : e e e n n n z z z y y y m m e e e s s s 1B C C C a a a t t t a a a l l l y y y s s s i i i s s s Most reactions take place with the help of third compounds, helpers or catalysts. Catalysts help and only help reactions to proceed, they do not have any effect on reaction equilibrium. They do not get used up during the reaction. They increase only the speed, the rate, with which the reaction approaches equilibrium Weve seen examples of biological catalysts: ATPases, kinases, polymerases. Collectively, biological catalysts are called enzymes. The effect catalysts have on the reaction is to lower its activation energy. Activation energy is a hump in an energy profile between products and substrates that must be overcome before the reaction proceeds. Activation energy exists for both exergonic and endergonic reactions Fig. 8-14 Progress of the reaction Products Reactants G < O Transition state F r e e e n e r g y E A D C B A D D C C B B A A Fig. 8-15 Progress of the reaction Products Reactants G is unaffected by enzyme Course of reaction without enzyme F r e e e n e r g y E A without enzyme E A with enzyme is lower Course of reaction with enzyme 2B M M M e e e c c c h h h a a a n n n i i i s s s m m m o o o f f f C C C a a a t t t a a a l l l y y y s s s i i i s s s Reactions proceed faster because: the enzyme increases the concentration of substrates by holding two molecules in physical...
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