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, onlychanged from oneform to another. 2) A change will alwaysbe accompanied byan 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

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 macromoleculesorganelles, etc.-anabolism

CO2 and H2O-catabolism

DH = DG + TDS

Gibbs Free Energy Equation:

Potential Energy

WorkEnergy

Energy Lostto Disorder

DG = DH - TDS

Rearranged:

Study of Energy Transformations: Thermodynamics

began w/ invention of steam engine

earlySteam Engine

DG = DH - TDS

Exergonic: DG < 0- will occur w/o external energy Endergonic: DG > 0- will NOT occur w/o external energy

& Products more disordered than Reactants (DS>0)Products have lower bond energies than Reactants (DH<0)

DH<0 and DS > 0DG < 0 (will occur w/o external energy) when:

OR DH<<<<0 and DS < 0OR DH>0 and DS >>>> 0

∆G measures likelihood a reaction will occur

Chemical Bond Energy

< Cell

.

Respiration

Fig. 3-4

Cell Respiration: DH <<< 0 allows DS < 0

DG = DH - TDS

Chemical Energy from Glucose Used to Synthesize Macromolecules

energy releasing

Fig. 3-2

energy consuming

DG < 0 DG > 0DH < 0, DS > 0 DH > 0, DS < 0

How Can Endergonic Reactions (DG >0) Occur in Cells?

Fig. 3-17

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)H2

hydrolysissynthesis

Fig. 3-31

Energy from Glucose Oxidation Storedin Activated Energy Carrier, ATP

Examples:

Panel 3-1g

NADH and NADPH are Activated Carriers of Electrons

Fig. 3-34

Electrons are transferred from glucose to these portable electron carriers.

.

DG under non-standard conditions (in cells) depends on true concentrations of molecules

Rxn 1DG>0

Rxn 2DG<<0

Coupled RxnDG<0

Rxn 2 keeps [Prod]/[React] of Rxn 1 low

DG = DGo + 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 Energyat 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 glucosein 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. 3-27v = Vmax [S] KM + [S]

Fig. 3-28

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 Vmax and KM

Fig. 3-27c 1/v = KM (1/[S]) + 1/Vmax

Vmax straight line formula: y = a(x) + b

Enzyme Kinetic Assays Can be Used to Evaluate Drugs

Fig. 3-29

+ competitiveinhibitor

+ competitiveinhibitor

+ noncompetitiveinhibitor

+ noncompetitiveinhibitor