Figure 6.1 The complexity of metabolism

METABOLISM Metabolism – totality of chemical reactions in cells Catabolic pathways- breakdown molecules to produce energy Anabolic pathways- build molecules by consuming energy

Figure 6.10 The ATP cycle

Unit 2 – How do cells regulate chemical reactions? Controlling reactions requires controlling thermodynamics and kinetics Thermodynamics – can a reaction happen? How much energy will need to be added or will be released? Kinetics – how fast will a reaction happen? (Determined by height of Ea); spontaneous rxns can be very slow

Figure 6.12 Energy profile of an exergonic reaction Link Free Energy (G) – which is favored at equilibrium – reactants or products? How much work can be obtained from a rxn?

Spontaneous Processes Processes that are spontaneous in one direction are nonspontaneous in the reverse direction. Spontaneous ≠ Fast

Key Concepts of Thermodynamics Enthalpy, H - heat energy change in a reaction (at constant pressure); the result of making and breaking chemical bonds Entropy, S - measure of disorder or # of possible arrangements of particles (microstates) Gibb’s Free Energy, G – amount of energy available to do work; sign of ΔG determines whether a process will occur spontaneously

3 Laws of Thermodynamics 1st Law (Conservation of Energy) – energy is neither created nor destroyed, only transformed. 2nd Law – The Entropy of the Universe always increases. 3rd Law – Defn of Zero Entropy – perfect crystalline solid at 0 K.

First Law of Thermodynamics “You can’t win” Energy can be neither created nor destroyed; it can only be transformed from one form to another Example: Transformation of potential energy -> kinetic energy Chemical potential energy – energy stored in chemical bonds Biological Example – Cellular respiration releases stored in energy in glucose, converts it into work and heat

Entropy Entropy(S)- measure of randomness or disorder Mathematically entropy is determined by the # of arrangements or microstates possible

3rd Law of Thermodynamics – Definition of Zero Entropy Zero entropy = perfect crystalline solid at 0 K (absolute zero) – only 1 possible microstate Microstate = Atom = Perfect crystal at 0 K = 1 microstate

Third Law of Thermodynamics The entropy of a pure crystalline substance at absolute zero is 0.

↑Microstates, ↑ Entropy Atom = 0 K - 1 microstate 0.001 K – 3 microstates(entropy increasing) 0.002 K – 5 microstates (entropy increasing)

.001 K – 3 microstates (entropy ↑) Atom = Arrangement 1: Arrangement 2: Arrangement 3:

Entropy, letters and Shakespeare’s Julius Caesar High Entropy Low Entropy - Rich in Meaning and Symbolism There is a tide in the affairs of men, Which, taken at the flood, leads on to fortune; Omitted, all the voyage of their life Is bound in shallows and in miseries.

Entropy and Molecules of Life CONSIDER 3 AMINO ACIDS: Ala, Gly, Lys Ala Gly Lys vs. Ala – Gly - Lys (separated) (bonded) Bonded together = much more order, especially if a specific sequence is required KEY CONCEPT: Biological molecules have extremely low entropy (highly ordered) because the components have to be bonded in a very specific sequence and have a very specific 3-D shape – conformation.

Entropy and the Second Law of Thermodynamics – “You can’t even break even” The natural tendency in the universe is towards maximum disorder. For any spontaneous process, the entropy of the universe increases ∆Suniv = ∆Ssystem + ∆Ssurroundings 2nd Law: ∆Suniv is always +

Does the existence of Life Violate the 2nd Law of Thermodynamics? No. ∆Suniv = ∆Ssystem + ∆Ssurroundings ∆Suniv is always +. ∆Ssurroundings > ∆Ssystem Heat flowing out of living organism increases entropy of its surroundings. Metabolizing Food is the price we pay for overcoming entropy to produce order. Heat released ↑ entropy of surroundings.

Figure 6.4 Order as a characteristic of life

Does Entropy explain Death? All living organisms that have ever existed on earth have eventually died. There seems to be a limit as to the # of times cells can divide. One theory – accumulated mutations (disorder!?) in DNA eventually causes too much chaos to sustain life

Gibbs Free Energy If DG is negative, the forward reaction is spontaneous. If DG is 0, the system is at equilibrium. If G is positive, the reaction is spontaneous in the reverse direction.

Gibb’s Free Energy, G ∆G = Change in Free Energy for a reaction Sign of ∆G indicates whether a process is spontaneous under a given set of conditions Value of ∆G indicates the maximum amount energy of theoretically available to do work Actual amount of work done is always less because some energy will be lost as heat (2nd Law of Thermodynamics)

Free Energy Changes Very key equation: This equation shows how G changes with temperature. (We assume S° & H° are independent of T.)

Free Energy and Temperature There are two parts to the free energy equation: H— the enthalpy term TS — the entropy term (T in Kelvin) The temperature dependence of free energy comes from the entropy term.

Spontaneous Processes Processes that are spontaneous at one temperature may be nonspontaneous at other temperatures. Above 0C it is spontaneous for ice to melt. Below 0C the reverse process is spontaneous.

Sign of ∆G Predicts whether a process will occur spontaneously If ∆G = -, rxn is spontaneous (can occur without outside intervention) If ∆G = +, rxn is not spontaneous If ∆G = 0, system is at equilibrium- no work can be obtained from reactions Note: spontaneous does not necessarily mean fast; speed is the realm of kinetics

Figure 6.6 Energy changes in exergonic and endergonic reactions Measure of maximum amount of work that can be obtained

Figure 6.5 The relationship of free energy to stability, work capacity, and spontaneous change