1. An Introduction to Metabolism

2. Metabolism/Bioenergetics  Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell 1. Catabolic pathways: degradative process such as cellular respiration; releases energy  Exergonic 2. Anabolic pathways: building process such as protein synthesis; photosynthesis; consumes energy  Endergonic

3. Thermodynamics  Energy (E): capacity to do work;  Kinetic energy: energy of motion  Potential energy: stored energy  Thermodynamics: study of E transformations  1st Law: conservation of energy; E transferred/transformed, not created/destroyed  2nd Law: transformations increase entropy (disorder, randomness)  Combo: quantity of E is constant, quality is not

4. Free energy (G)  Free energy: portion of system’s E that can perform work (at a constant T)  Exergonic reaction: net release of free E to surroundings (ΔG<0) - spontaneous  Endergonic reaction: absorbs free E from surroundings (ΔG>0) – NOT spontaneous

5. Gibb’s Free Energy Formula  ΔG = ΔH - T ΔS  ΔG = Gibb’s Free Energy, the amount of free energy available to a system  Unit = kJ (kiloJoules)  ΔH = heat of reaction (or Enthalpy), the amount of heat energy in a system  Unit = kJ (kiloJoules)  T = temperature  Unit (Kelvin  ̊C + 273)  ΔS = entropy, the amount of order/disorder in a system  Unit = J/K (Joules per Kelvin)

6. What it means  ΔG – positive vs. negative  + ΔG = reaction is endergonic (energy must be supplied to make the reaction occur)  - ΔG = reaction is exergonic (generally, this reaction is spontaneous and releases energy)  ΔH – positive vs. negative  + ΔH = reaction is endothermic (heat energy is absorbed from the surrounding area)  - ΔH = reaction is exothermic (heat energy is released into the surrounding area)

7. What it means  ΔS – positive vs. negative  + ΔS = the entropy of the system in increasing (you have more free moving molecules, things are breaking apart, catabolism)  - ΔS = the entropy of the system is decreasing (you have more structured arrangement of molecules, tends to be fewer, more complex, molecules, anabolism)  EXAMPLE: HC 2 H 3 O 2 has less entropy than 2 H + (more number of molecules as opposed to just more atoms in molecule)

8. EXAMPLE  A biological reaction has an exothermic reaction (ΔH) that produces -55.8kJ of energy. If the reaction is decreasing entropy (ΔS) by -0.35kJ/K at a temperature of 25°C, what would be the free energy (ΔG)? Is this reaction exergonic (releasing energy) or endergonic (absorbing energy)?

9. SOLUTION  ΔG = ?  ΔH = -55.8kJ  ΔS = -0.35kJ/K  T = 25°C  = 298K  ΔG = ΔH – TΔS  ΔG = -55.8kJ – (298K)(-0.35kJ/K)  ΔG = -55.8kJ + 104.3kJ  ΔG = +48.5kJ  NOTE: The reaction is endergonic

10. QUESTIONS  How do you think the following affects Free Energy? Does it make it more likely to happen or less likely? 1. Increasing the temperature of a system? 2. Decreasing the entropy? 3. Decreasing the enthalpy (heat of reaction)?

11. ENERGETICS AND REACTIONS  All reactions need energy to start (Energy of activation)  Many times this energy cost is insurmountable  Strategies to deal with energy cost  Couple reaction with another exergonic reaction  Enzymes to reduce energy of activation

12. Energy Coupling & ATP  E coupling: use of exergonic process to drive an endergonic one (ATP)  Adenosine triphosphate  ATP tail: high negative charge  ATP hydrolysis: release of free E  Phosphorylation (phosphorylated intermediate): enzymes  KINASES

13. Enzymes: LOCK AND KEY MODEL  Catalytic proteins: change the rate of reactions w/o being consumed  Free E of activation (activation E): the E required to break bonds  Substrate: enzyme reactant  Active site: pocket or groove on enzyme that binds to substrate  Induced fit model

14. Effects on Enzyme Activity  Temperature  pH  Cofactors:  inorganic, nonprotein helpers; ex.: zinc, iron, copper  Coenzymes:  organic helpers; ex.: vitamins

15. Rate of enzyme activity  There are many actions that can speed up the rate of enzyme activity (already discussed)  Optimal pH, increased temp, increased amount of enzyme, increased amount of substrate  Regardless of optimal concentrations, thing always limits the enzyme rates  Amount of enzyme  Once you have “maxed” out the use of enzymes, the rate of reaction is constant

16. Enzyme Inhibitors  Irreversible (covalent); reversible (weak bonds)  Competitive : competes for active site (reversible); mimics the substrate  Noncompetitive : bind to another part of enzyme (allosteric site) altering its conformation (shape); poisons, antibiotics