Fig. 1-7 Chapter 3 Energy, Catalysis, and Biosynthesis By maintaining highly ordered states, cells seemingly defy the laws of thermodynamics: 1) There is a finite amount of energy in the universe. It can neither be created nor destroyed, only changed from one form to another. 2) A change will always be accompanied by an increase in disorder.

The same principle applies to our everyday lives. A housewife’s work is never done….Neither is the cell’s. Fig. 3-4

Thermodynamics: Study of Energy Transformations Fig. 3-6

Photosynthesis Makes Sugars for Cellular Respiration

All energy required to maintain life is derived from the sun. Fig. 3-7 Vincent van Gogh

Chemical Energy from Glucose Used by Cells to Synthesize Macromolecules energy releasing Fig. 3-2 energy consuming

Cells Do Not Defy the Laws of Thermodynamics in the Context of the Whole Universe Fig. 3-5 macromolecules organelles, etc. -anabolism CO 2 and H 2 O -catabolism

 H =  G + T  S Gibbs Free Energy Equation: Potential Energy Work Energy Energy Lost to Disorder  G =  H - T  S Rearranged: Study of Energy Transformations: Thermodynamics began w/ invention of steam engine early Steam Engine

 G =  H - T  S Exergonic:  G 0- will NOT occur w/o external energy & Products more disordered than Reactants (  S>0) Products have lower bond energies than Reactants (  H<0)  H 0  G < 0 (will occur w/o external energy) when: OR  H<<<<0 and  S < 0 OR  H>0 and  S >>>> 0 ∆G measures likelihood a reaction will occur Chemical Bond Energy < Cell

. Respiration

Fig. 3-4 Cell Respiration:  H <<< 0 allows  S < 0  G =  H - T  S

Chemical Energy from Glucose Used to Synthesize Macromolecules energy releasing Fig. 3-2 energy consuming  G < 0  G > 0  H 0  H > 0,  S < 0

How Can Endergonic Reactions (  G >0) Occur in Cells? Fig One mechanism is to couple it to a highly exergonic reaction.

Chemical Energy from Glucose Used to Synthesize Macromolecules energy releasing Fig. 3-2 energy consuming Activated Energy Carriers ATP, NAD(P)H 2

hydrolysissynthesis Fig Energy from Glucose Oxidation Stored in Activated Energy Carrier, ATP

Examples: Panel 3-1g

NADH and NADPH are Activated Carriers of Electrons Fig Electrons are transferred from glucose to these portable electron carriers.

.

 G under non-standard conditions (in cells) depends on true concentrations of molecules Rxn 1  G>0 Rxn 2  G<<0 Coupled Rxn  G<0 Rxn 2 keeps [Prod]/[React] of Rxn 1 low  G =  G o + RT ln [Product] [Reactant] Fig. 3-21

. will occur without external energy, but not on useful timescale

without enzyme with enzyme Fig. 3-27b (modified) Enzymes Increase the Velocity of a Reaction (Not the Thermodynamics)

Enzymes Lower Activation Energy Fig. 3-12

Enzymes Lower Activation Energy Fig. 3-14

By Lowering Activation Energy at Discrete Steps, Enzymes Direct Reaction Pathways Fig. 3-14

Enzymes are not altered by the reactions they catalyze. They used over and over again. Fig. 3-15

Enzymes allow the cell to extract energy from glucose in small steps, instead of all at once in the form of heat. Some energy can be harnessed for useful work. Fig. 3-30

How Do Enzymes Lower the Activation Energy? Fig. 4-36

Example: Lysozyme Amino acid side chains at active site alter chemical properties of substrate to ease it into activated transition state. bond bent, then broken by enzyme Fig. 4-35

Measuring Enzyme Performance Fig v = V max [S] K M + [S]

Fig A stopped-flow apparatus is needed to catch the initial velocity. We do the best we can with what we have.

Double Reciprocal Plot Allows for Easier Determination of V max and K M Fig. 3-27c 1/v = K M (1/[S]) + 1/V max V max straight line formula: y = a(x) + b

Enzyme Kinetic Assays Can be Used to Evaluate Drugs Fig competitive inhibitor + competitive inhibitor + noncompetitive inhibitor + noncompetitive inhibitor