1. Chapter 6 Energy and Metabolism

2. Energy: The capacity to do work – any change in the state of motion or matter Measured as heat energy Unit is the kilocalorie (K) Heat energy flows from an object of higher temperature to an object of lower temperature Cells cannot use heat energy for work because they are too small for a significant temperature gradient

3. Types of energy: Potential energy - the capacity to do work based on position or state –Chemical energy is potential energy stored in chemical bonds –Food is a type of chemical (potential) energy Kinetic energy – the energy of motion –Mechanical energy is kinetic energy of motion –Muscular movement is mechanical (kinetic) energy

4. Types of energy systems: Closed – the system does not exchange energy with its surroundings Open – the system does exchange energy with its surroundings Are biological systems closed or open? Why?

5. Thermodynamics The study of energy and its transformations First law of thermodynamics –Energy cannot be created or destroyed –Energy can be transferred or changed in form –Organisms cannot create energy but can capture it Second law of thermodynamics –No energy transfer is 100% efficient –Some energy is lost as heat and cannot be used to do work –Organisms fight entropy only with constant input of energy from their surroundings

6. Metabolism Needed for organism’s life processes The sum of all chemical activities within an organism Two processes: 1.Anabolism – requires energy input Complex molecules are synthesized from simpler substances 2.Catabolism – releases energy Larger molecules are broken down to smaller ones In living systems catabolism usually supplies the energy needed for anabolism

7. Types of reactions: Exergonic – spontaneous or downhill –Releases energy that can perform work –Products have less energy than the reactants Endergonic – nonspontaneous –Energy must be supplied from the environment –Products will have more energy than the reactants

9. ATP: Adenosine triphosphate Holds energy for very short periods Releases energy when third phosphate group is removed: ATP  ADP + P Links exergonic and endergonic reactions – used for catabolism and anabolism

10. ATP and ADP Nucleotides: –Adenine –Ribose –Phosphate groups ATP = three phosphates ADP = two phosphates Moving from ATP to ADP releases energy in an exergonic reaction

11. Redox Reactions OIL RIG: –Oxidation is lost; reduction is gain Energy moves with the electrons: –The substance that becomes oxidized gives up energy (and an electron) –The substance that becomes reduced gains energy (and an electron) Always paired in biological systems – free electrons cannot exist in nature Redox reactions in cells generally involve the transfer of a whole hydrogen atom rather than just an electron

12. Acceptor molecules... NAD+ gains H atom (is reduced) to form NADH NADH stores large amounts of energy This energy is transferred in a series of reactions to other molecules that will eventually form ATP NADP+ is chemically similar Reduced to form NADPH, but this is not involved in ATP formation

13. NAD+(oxidized) to NADH (reduced)

14. Enzymes Are biological catalysts Cells need enzymes to regulate the rate of chemical reactions These work by lowering the activation energy of a chemical reaction (energy required to break existing bonds) Although most enzymes are proteins, some types of RNA molecules have catalytic activity as well

15. Enzymes… Enzyme + substrate  enzyme-substrate complex ES complex  enzyme + product(s) The enzyme is not permanently altered by the reaction and can be reused The substrate joins to the enzyme at the active site As the substrate joins the enzyme – it causes a shape change – induced fit Enzymes are specific – the shape of the substrate must fit

17. Enzymes… Work best at specific temperature and pH conditions Catalyze virtually every chemical reaction that takes place in an organism Some enzymes consist only of protein Some enzymes have two components –Protein called apoenzyme –Cofactor

18. Control of reactions: Inhibition Feedback inhibition: Formation of an end product inhibits an earlier reaction in the metabolic pathway

19. Inhibition… Competitive inhibition –Inhibitor competes for the substrate for the active site Noncompetitive inhibition –Inhibitor binds with enzyme at a site other than active site Irreversible inhibition –Inhibitor combines with an enzyme and permanently inactivates it

20. Competitive and noncompetitive inhibition