Metabolism ConceptsThermodynamics applies to metabolism

DG (but not DGº) must be negative for a process to occur.If DG for a process is (+), then the process will occur in reverse.

DG = DGº + RT ln Q and DGº = -RT ln K

DG = DH - TDS Free energy to drive reactions in living systems is found in a number of “high energy” molecules. ATP or other nucleoside triphosphates (GTP, CTP, TTP, UTP) Reduced ‘coenzymes’ (NADH and FADH2) Thioester coupling (e.g. AcetylCoA , fattyacylCoA)

Living organisms do not violate the 2nd law of thermodynamics

In the process of transforming energy, living organisms must increase the entropy of the universe. Living systems accomplish this by taking “ordered” energy from their surroundings (carbohydrates, lipids, and proteins) and returning disordered energy (heat, CO2, H2O) back to their surroundings.

All reactions/processes that occur in a living organismMetabolism

1. Generate Useable Energy Catabolic/catabolism

Provides cellular energy/ATP

2. Synthesize Molecules/structures Anabolic/anabolism requires energy/ATP

I digestion/hydrolysis Macromolecules → fuels

II Oxidation of fuel Glycolysis – glucose b-oxidation – FAs oxidative deamination - Pro makes NADH/FADH2

III ATP productionKrebs cycle &Oxidative phosphorylation

Stages of Catabolism (and to some degree Anabolism)

triglycerides → glycerol + fatty acids lipase (intestines & adipose)

proteins → peptides various proteases (stomach & intestines) pepsin trypsin and chymotrypsinpeptides → amino acids aminopeptidase and carboxypeptidase

polysaccharides → mono/di saccharides amylase (saliva & intestines) starch → maltose & glucose sucrase/invertase sucrose → fructose & glucose (intestines) lactase (absent in lactose intolerance) lactose → galactose & glucose (intestines)

I digestion/hydrolysis Macromolecules → fuels

All reactions/processes that occur in a living organismMetabolism

PATHWAY

metabolic intermediates — a molecule transiently produced in a pathwayMetabolite — a molecule produced from some ingested/absorbed molecule

A BE1

C D E FE2 E3 E4 E5

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

C4

ATP

Glycolysis

Bridging Rx.

Oxidative PhosphorylationADP

O2

NAD+/FAD

Metabolic Mainstreet1. Generate Useable Energy (ATP) Catabolic

2. Synthesize Molecular “Parts” Anabolic

NAD+

FAD

Dehydrogenases Oxidative Phosphorylaton

fuel in

SH2 NADH ATP

S NAD+ ADP

work output

ATP uses

Drive anabolic reactions

Mechanical Motion (e.g. Muscles)

Active Transport — maintain membrane gradients

ATP + H2O ADP + Pi DG° = -7.3 kcal/mol

[ATP] + 1/2[ADP] [ATP] + [ADP] + [AMP]

Energy charge

DG = DG + RT ln Q

DG = DH - DS at equilibrium ……DG = 0, Q = Keq & DG = - RT ln Keq

ATP + H2O ADP + Pi DG° = -7.3 kcal/mol

Transition state

Activation energy - related to rate

ATP + H2O

DGº = -7.3 kcal/mol ADP +

Pi

ATP useDrive anabolic reactions

Mechanical Motion (e.g. Muscles)

Active Transport — maintain membrane gradients

ATP + H2O ADP + Pi DG° = -7.3 kcal/mol

PPi + H2O 2Pi DGº′ = -8.0 kcal/mol

ATP + H2O AMP + PPi DG° = -7.3 kcal/mol

ADP + H2O AMP + Pi DG° = -7.3 kcal/mol

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Energy Charge (EC)

Rate

catabolic

anabolic

[ATP] + 1/2[ADP] [ATP] + [ADP] + [AMP]

Energy charge

0 1 with AVG 0.85

EC

ATP, ADP, and AMP are common allosteric enzyme regulators

Cellular ATP concentration is usually far above the equilibrium concentration, making ATP a very potent source of chemical energy.

Average [ ]’s in muscle cells

[ATP] 8mM

[ADP] [AMP] 1mM

[Pi] 8mM

DG = DG + RT ln Q

ATP + H2O ADP + Pi DG = -7.3 kcal/mol

“ An Organism at equilibrium is a dead organism!”“A Cell is always striving to achieve a state of equilibrium, but never succeeding”

Q = [ADP] • [Pi] [ATP]

DG = DH - DS at equilibrium ……DG = 0, Q = Keq & DG = - RT ln Keq

Q = 1x10-3 • 8 x 10-3 = 1 x 10-3. 8 x 10-3

DG = -7.3+ 0.62 ln (0.001) = -11.6 kcal

Enzymatic ATP hydrolysis helps a cell to utilize ATP energy for useful purposes, faster than it will hydrolyze non-enzymatically to generate heat.

Parallel or Kinetic Coupling X + Pi X-P DG = + 5.0

ATP ADP + Pi DG = -7.3

Enzyme = “X” Kinase

X + ATP X-P + ADP DG = -2.3

Series or Thermodynamic CouplingX Y Z

X Y DG˚′ = + 4.0 [Y] << [X]

Y Z DG˚′ = -5.0 [Y] <<< [Z]

X Z DG˚′ = -1.0 [X] < [Z]

Glucose + Pi Glucose-6-P + H2O What is DG°´ for this reaction?

Addition of phosphate is the opposite of hydrolysis....DG°´ = +3.3 kcal/mol

Calculate [G-6-P]/[Glucose] at equilibrium ([Pi] 8mM) DG = - RT ln Keq [G-6-P]/[Glucose] ~ 3.8 x 10-5

DG = - RT ln Keq & [G-6-P]/[Glucose] = 634

Glucose + ATP Glucose-6-P + ADP (assume [ATP] = [ADP]) DG°´ = +3.3 – 7.3 = -4.0

Without coupling[G-6-P]/[Glucose] ~ 3.8 x 10-5

Coupling with ATP hydrolysis shifted equilibrium > 10 million x not a true equilibrium but rather a steady state

Which molecule is more stable …… a) creatine b) creatine phosphate

Which molecule is more stable …… a) 1,3 bisphosphoglycerate b) creatine phosphate

What is DG°′ for the reaction ……. 1,3 bisphosphoglycerate + ADP ↔ 3 BPG + ATP a) -22.1 kcal mol-1 b) -4.5 kcal mol-1 c) +4.5 kcal mol-1 d) none of these

Macromoleculesdigestion/hydrolysis fuels

various catabolic pathways NADH/FADH2

Krebs cycle & oxidative phosphorylation ATP

ATP uses

Drive anabolic reactions

Mechanical Motion (e.g. Muscles)

Active Transport — maintain membrane gradients

ATP + H2O ADP + Pi DG° = -7.3 kcal/mol

[ATP] + 1/2[ADP] [ATP] + [ADP] + [AMP]

Energy charge

DG = DG + RT ln Q

DG = DH - DS at equilibrium ……DG = 0, Q = Keq & DG = - RT ln Keq

Glucose

AcetylCoA

Pyruvate

NADH/FADH2

KrebsCycle

C6

C4

C5

C4

ATP

Glycolysis

Bridging Rx.

OP

ADP O2

NAD+/FAD

Metabolic Mainstreet

PATHWAYS: 4 W’sWhat = Net Reaction

Why = Purpose(s) of Pathway

Where = Organism/Tissue/Organelle

When = Regulation of Pathway

Hydrolysis of ATP is highly favorableunder standard conditions

• Better charge separation in products

• Better solvation of products

• More favorable resonance stabilization of products

Actual DG of ATP hydrolysis differs from DG’

• The actual free-energy change in a process depends on:– The standard free energy– The actual concentrations of reactants and products

• The free-energy change is more favorable if the reactant’s concentration exceeds its equilibrium concentration

• True reactant and the product are Mg-ATP and Mg-ADP, respectively– DG also Mg++ dependent

]MgATP[]P[]MgADP[ln' 2

i-

- DD RTGG

Hydrolysis of Thioesters

Reduction Potential• Reduction potential (E)

– Affinity for electrons; higher E, higher affinity– Electrons transferred from lower to higher E

DE’ = -(RT/nF)ln (Keq) = DG’/nF

∆E’ = E’(e- acceptor) – E’(e- donor)

∆G’ = –nF∆E’For negative DG need positive DE

E(acceptor) > E(donor)

NAD and NADP are common redox cofactors