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Enzymes

Enzymes. Thermodynamically spontaneous  kinetically feasible. Example: hydrolysis of ATP. ATP + H 2 O ADP + P i. G °´= -7.3 kcal/mole. Requirements for chemical reactions. Collide with each other Conc. dependent Collide with enough energy Kinetic energy i.e., temperature

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Enzymes

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  1. Enzymes

  2. Thermodynamically spontaneouskinetically feasible

  3. Example: hydrolysis of ATP ATP + H2O ADP + Pi G°´= -7.3 kcal/mole

  4. Requirements for chemical reactions • Collide with each other • Conc. dependent • Collide with enough energy • Kinetic energy i.e., temperature • Collide with right orientation • When these are met, reaction occurs via a transition state • High energy • Unstable

  5. Transition State Formation The energy required to get to the transition state is the Activation Energy

  6. G°´= -7.3 kcal/mole Rate of reaction depends on number of molecules that have energy greater than or equal to EA

  7. Requirements for chemical reactions • Collide with each other • Collide with enough energy • Collide with right orientation How can we speed reactions up?

  8. Ways to speed up a reaction • Increase concentration of reactants • Increase temperature • Decrease activation energy barrier

  9. Equilibrium (and G) do not change

  10. Catalysts • Increase reaction rates by lowering activation energy barriers • Form transient complexes with substrate molecules and transition state • Stabilize the transition state via favorable interactions • Changes rate, not equilibrium • Does NOT provide energy

  11. Enzymes: Biological Catalysts • Extremely high catalytic rates • Diffusion limited • Very specific • Function in aqueous solution • Mild temp. • Neutral pH • Can be regulated

  12. Terms • Cofactor • Ions • Complex organic/organometallic groups • AKA coenzymes • Prosthetic group • Covalently bound cofactor • Apoenzyme/protein • Holoenzyme/protein • Active Site • Binding Site • Substrate

  13. Enzymes: Biological Catalysts • Extremely high catalytic rates • Very specific • Function under mild temp./pH • But limited in temp./pH • Can be regulated HOW? Because they are proteins

  14. Enzymes are flexible • Essential for • Substrate specificity • Regulation

  15. Active Sites A tertiary level structure

  16. How does the substrate bind to the active site? • Lock and key model • Induced fit model

  17. Example: carboxypeptidase

  18. Substrate Activation(catalytic mechanisms) • Strain on substrate • Weakens bonds • Makes more accessible for reaction • Acid/base catalysis • Covalent (nucleophilic) catalysis

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