The 2 nd Law of Thermodynamics

1. The 2nd Law of Thermodynamics • With every energy transfer, entropy is increased • Entropy = disorder (or randomness) • In an energy transfer or transformation, some energy becomes unusable and is released as heat

2. Heat co2 + H2O Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are WASTE of metabolism. An example of 2nd Law of Thermodynamics

3. DECOMPOSITION also increases entropy

4. No chemical rxn is 100% efficient b/c not all energy is converted into work

6. Entropy & The Universe • The entropy/randomization of the whole universe is constantly increasing in an unstoppable fashion. • Organisms are rather highly ordered… so organisms are like islands of low entropy in an increasingly random universe that contains a lot of entropy

7. 2nd Law of Thermodynamics TOTAL ENERGY (enthalpy, H) = usable energy + unusable energy • Entropy = increase in disorder • The unusable energy • Usable energy= increase in order

8. Free-Energy known as “G” • Usable energy that can do work (in a living cell) • Known as Gibb’s Free Energy • Needed to maintain healthy cell growth, division, etc.

9. ∆G = ∆H – T∆S • ∆Gis the change in free energy during a biological process/chemcialrxn • related directly to the change in enthalpy (∆H) and the change in entropy (ΔS) • ∆H= change in the system’s total energy (usable + unusable energy) • ∆S = change in entropy • T = absolute temp (K)(°C + 273)

10. Why is ∆G helpful? • It tells us if a chemical rxn will occur spontaneously (without outside input of energy) • Negative ∆G: occurs spontaneously (loses free energy) • The free energy that is lost can be used by the cell to perform work, keeping the cell alive and functioning! So, spontaneous rxns allow the cell to perform work! • + or zero ∆G: rxn does not occur spontaneously (requires input of energy)

11. Reminder about Spontaneous reactions • (Spontaneous reactions are reactions that occur without the input of energy.) • Examples: • Water flows downhill • A car rusts • Non-examples: • Water moves uphill • Only happens with input of energy, ie. a pump

12. Free Energy and Metabolism • 2 types of Reactions in Metabolism • Exergonic (Exothermic) • Endergonic (Endothermic)

14. Reactants Amount of energy released (∆G <0) Energy Free energy Products Progress of the reaction (a) Exergonic reaction: energy released Exergonic and Endergonic Reactions in Metabolism • An exergonic reaction (- ∆G) • Proceeds with a net release of free energy and IS spontaneous

15. Exergonic reactions • The magnitude of ΔG represents the maximum amount of work that the reaction can perform. • When you break down a polymer into a monomer (exergonic/catabolic rxn), energy is released. The ΔG number symbolizes the amount of this energy that is released. This released/”free” energy can be used to perform work.

16. Products Amount of energy released (∆G>0) Energy Reactants Free energy Progress of the reaction Figure 8.6 (b) Endergonic reaction: energy required • Endergonic reactions (+ ∆G) • absorbs free energy from its surroundings and is NOT spontaneous • Stores free energy in molecules, so ΔG is positive Madnitude of GRepresents amt of energy needed to drive rxn

17. Catabolic reactions Anabolic reactions

18. If a reaction is exergonic (downhill) in one direction, the reverse reaction must be endergonic (uphill). • If ΔG for a reaction is -20 kcal/mol, then ΔG for the reverse reaction = +20 kcal/mole

19. Real Life Examples… • Exergonic (Exothermic) • Cellular Respiration • Energy is released when glucose is broken down • Endergonic (Endothermic) • Photosynthesis • Energy is NEEDED (consumed) to put together glucose from CO2, H20 and sunlight

20. Energy coupling/ coupled reactions • Two reactions that occur nearly simultaneously. The first rxn (exothermic, spontaneous), gives off energy and the second rxn(endothermic, non-spontaneous) uses that energy. Spontaneous rxn: A + B  C + D + energy -ΔG Non-spontaneous rxn: E + energy  F +ΔG

21. Coupled Reactions

22. ATP • An energy-containing molecule that is produced by the exergonic reaction and used in the endergonic reaction during energy coupling. • Major source of energy in cells when they do work

23. ATP powers cellular work by coupling exergonic rxns to endergonic rxns • A cell does three main kinds of work • Mechanical = ex: movement (ie. moving chromosomes during cell division) • Transport = ex: passive & active cell membrane transport • Chemical = ex:the pushing of endergonic rxns(ie. synthesizing polymers from monomers)

24. The Structure and Hydrolysis of ATP • ATP (adenosine triphosphate) • Is the cell’s energy shuttle (molecule) • Provides energy for cellular functions • It is renewable (A nitrogenous base) high energy bonds

25. P P P Adenosine triphosphate (ATP) H2O Free Energy given off + P i P P + Adenosine diphosphate (ADP) Inorganic phosphate • Energy is released from ATP when the terminal phosphate bond is broken • Happens via a hydrolysis reaction • Exergonic rxn(ΔG= -7.3 kcal/mol) Sometimes referred to as “high energy” phosphate bonds

26. Endergonic reaction (synthesis of glutamine): ∆G is positive, reaction is not spontaneous NH2 NH3 + ∆G = +3.4 kcal/mol Glu Glu Glutamine Glutamic acid Ammonia Exergonic reaction (hydrolysis of ATP): ∆ G is negative, reaction is spontaneous ∆G = - 7.3 kcal/mol + P ADP H2O ATP + Coupled reactions: Overall ∆G is negative; together, reactions are spontaneous ∆G = –3.9 kcal/mol • ATP hydrolysis can be coupled to other reactions

27. O– O– O– O– O– O– P P P P P P –O –O –O O– O– O– –O –O O– O– –O O– O O O O O O How does ATP store energy? I thinkhe’s a bitunstable…don’t you? • Each negative PO4 more difficult to add • a lot of stored energy in each bond • most energy stored in 3rd Pi • 3rd Pi is hardest group to keep bonded to molecule • Bonding of negative Pi groups is unstable • spring-loaded • Pi groups “pop” off easily & release energy ATP Instability of its P bonds makes ATP an excellent energy donor

28. How ATP Performs Work • ATP drives endergonic reactions… • by phosphorylation, transferring a phosphate (PO43-) to other molecules/reactants (reactant becomes “phosphorylated”) • When this happens, ATP becomes ADP • Reactant is more reactive (less stable) with PO43- on it  acts as an intermediate in many rxns • Reactant + Pi is not the overall final product, but rather the product of the exergonic reaction which then is used in the endergonic reaction

29. The regeneration of ATP

30. Enzyme Inhibition of Metabolic Pathways • Competitive inhibitors • mimic the substrate and compete for the active site. • Non-competitive inhibitors • bind to enzyme away from active site  cause a change in the enzyme’s (and the active site’s) shape

32. Regulation of Enzyme Activity • A cell’s metabolic pathways must be tightly regulated • Regulating enzymes help CONTROL metabolism • Allosteric Regulation • when a protein’s function at one site is affected by binding of a regulatory molecule at another site

33. Allosteric Regulation & Enzymes • Regulatory molecules aremolecules that regulate/control/influence metabolism • bind to enzyme’s allosteric site  enzyme’s shape changes • Allosterically regulated enzymesare enzymes whose metabolic activities are regulated/controlled/influenced by enzymes • have a quaternary protein structure • Constructed from two or more polypeptide chains

34. Each subunit of the enzyme has an active site and an allosteric site. • Allosteric activatorsstabilizes active site • Allosteric inhibitorsdeactivates active site.

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