Chemistry Of Life : Reactions & Enzymes

1. Chemistry Of Life:Reactions & Enzymes Chapter 6

2. Chemical Reactions Chemical reactions have reactants and products. CO2(g) + H2O(l)  H2CO3(aq) Endothermic reactions must absorb heat to proceed Exothermic reactionsrelease heat

3. Energy and Entropy Energy The capacity to do work or supply heat Kinetic (movement); thermal Measured in temperature Potential (stored); chemical Entropy The amount of disorder in a group of molecules In general, physical and chemical processes proceed in the direction that results in lower potential energy and increased entropy.

4. The Laws of Thermodynamics • First Law of Thermodynamics • Energy is conserved—it cannot be created or destroyed, but it can be transferred or transformed. • Second Law of Thermodynamics • Entropy always increases • Chemical reactions result in products with less ordered (usable) energy

6. Gibbs Free-Energy Change (ΔG) Determines whether a reaction is spontaneous or requires energy.

7. Temperature and Concentration Affect Reactions The rate of a reaction depends upon the number of collisions between substances. The number of collisions is dependent on the temperature and concentration of the reactants: Higher temperature  more collisions  faster reaction Higher concentration  more collisions  faster reaction

8. Catalysis Reactions take place when: Reactants collide in precise orientation Reactants have enough kinetic energy to overcome repulsion between the electrons that come in contact during bond formation Enzymes perform two functions: Bring substrates together in precise orientation so that the electrons involved in the reaction can interact Decrease the amount of kinetic energy reactants must have for the reaction to proceed

10. Catalysts and Free Energy A substance that lowers the activation energy of a reaction and increases the rate of the reaction. Catalysts do not change ΔG and are not consumed in the reaction.

11. Enzymes Enzymes are protein catalysts and typically catalyze only one reaction. Most biological chemical reactions occur at meaningful rates only in the presence of an enzyme. Enzymes: Bring reactants together in precise orientations Stabilize transition states Proteincatalysts are important because they speed up the chemical reactions that are required for life.

12. How Do Enzymes Work? Enzymes bring substrates together in specific positions that facilitate reactions, and are very specific in which reactions they catalyze. Substrates bind to the enzyme’s activesite. Many enzymes undergo a conformational change when the substrates are bound to the active site; this change is called an induced fit. Interactions between the enzyme and the substrate stabilize the transition state and lower the activation energy required for the reaction to proceed.

14. The Steps of Enzyme Catalysis Enzyme catalysis has three steps: Initiation Substrates are precisely oriented as they bind to the active site. Transition state facilitation Interactions between the substrate and active site R-groups lower the activation energy. Termination Reaction products are released from the enzyme.

15. Do Enzymes Act Alone? Some enzymes require cofactors to function normally. These are either metal ions or small organic molecules called coenzymes.

16. Enzyme Regulation Competitive inhibition When a molecule similar in size and shape to the substrate competes with the substrate for access to the active site. Allosteric regulation When a molecule causes a change in enzyme shape by binding to the enzyme at a location other than the active site. Can activate or deactivate the enzyme

17. Enzyme Saturation The rate of a reaction is limited by the amounts of substrate present and available enzyme.

18. Optimal Conditions Enzymes function best at some particular temperature and pH. Temperature affects the movement of the substrates and enzyme. pH affects the enzyme’s shape and reactivity.