Why the big DGo’ for Hydrolyzing Phosphoanhydrides? • Electrostatic repulsion betwixt negative charges • Resonance stabilization of products • pH effects
pH Effects – DGo vs. DGo’ (DG in kcal/mol) WOW!
Cellular DGs are not DGo’ s DGo’ for hydrolysis of ATP is about -31 kJ/mol Cellular conditions are not standard, however: In a human erythrocyte, [ATP]≈2.25 mM, [ADP] ≈0.25 mM, [PO4] ≈1.65 mM
Activation with ATP - luciferin Excited state of oxyluciferin forms and decays
For those who prefer more detail Excerpted from Baldwin, T. (1996) Structure4: 223 – 228,
Just because it’s cool… Tobacco seedling w/ cloned luciferase Southeast Asian firefly tree
Just because it’s cool… Firefly squid (Watasenia scintillans) of Toyama Bay, Japan New Zealand glowworm (Arachnocampa) cave
“Phosphate Transfer Potential” is a fancy-schmancy term for –DGo’
Electrochemistry in review 1.10 V One beaker w/ ZnSO4 and a Zn electrode One beaker w/ CuSO4 and a Cu electrode Zinc gets oxidized and the electrode slowly vanishes Copper gets reduced and the electrode gets fatter
Redox Table • Higher the SRP, the better the oxidant • Lower the SRP, the better the reductant • Any substance can oxidize any substance below it in the table. • The number of reactants involved doesn’t change the reduction potential • i.e. if a reaction involves 2 NAD+, the SRP is still -0.32 V
Electrochemistry in review 1.10 V Zinc gets oxidized Copper gets reduced What determines who gets oxidized?
DEo and Keq For an actual half reaction aA + ne-⇌aA- For an actual redox reaction: A+n + ne- ⇌ A B ⇌ B+n + ne- A+n + B ⇌ A + B+n and (Analagous to the relation between DG and DGo’)
DEo and Keq (cont.) Atequilibrium, the two are equal: Combining: Or Or Or (rearranging) Dr. Ready gets to the Point!
DEo and DGo So: But we already know: Therefore: Another Point!
NAD+ Reduction(Nicotinamide Adenine Dinucleotide) NAD+ is a common redox cofactor in biochemistry
Coenzyme Q Coenzyme Q is another electron carrier in the cell
An Example: What is DGo’ for the Oxidation of NADH by Ubiquinone?
“Organic” ≠ “Healthy” Vomiting and nausea, diarrhea, Headaches, Difficulty breathing, Pallor, Sweating, Palpitations, Lisps, Stomach pains/cramps, Seizures, Weakness, Drooling, and - of course - Death
Metabolism • Energy (ATP) • Parts (amino acids, etc.) • Reducing Power (NADH, NADPH) Catabolism (Oxidation) Anabolism (Reduction)
Catabolism of Glucose C6H12O6 + 6O2 → 6CO2 + 6H2O DGo’ = -2870 kJ/mol It takes 31 kJ/mol to make an ATP. Enough energy is available for making ~90 (theoretically)
An aside on diets Glucose (a carb), mol. wt. = 180 g/mol -2870 kJ/mol = -686 kcal/mol -686 kcal/mol / 180 g/mol = 3.8 kcal/g Palmitic Acid (a fatty acid) mol. wt. = 256 g/mol -9959 kJ/mol = -2380 kcal/mol -2380 kcal/mol / 256 g/mol = 9.3 kcal/g Alanine (an amino acid) mol. wt. = 88 g/mol -1297 kJ/mol = -310 kcal/mol -310 kcal/mol / 88 g/mol = 3.5 kcal/g
An aside on diets (cont.) From Nutristrategy.com: Fat: 1 gram = 9 calories Protein: 1 gram = 4 calories Carbohydrates: 1 gram = 4 calories The diet values come from the DGo’ for oxidizing the various biomolecules.
Interconversion of C6 Sugars Glycogen Glucose-1-Phosphate -7.3 kJ/mol Glucose Glucose-6-Phosphate Amino Sugars -0.4 kJ/mol Nucleotides Fatty Acids Fructose-6-Phosphate Catabolism
Glucose Catabolism Part 1:Glycolysis • Aka Embden-Meyerhof pathway • Worked out in the 1930’s • Partially oxidizes glucose • Uses no O2 • Takes place in cytoplasm
Interconversion of C6 Sugars (Again) Glycogen Glucose-1-Phosphate -7.3 kJ/mol Phosphoglucomutase Glucose Glucose-6-Phosphate Amino Sugars -0.4 kJ/mol Phosphohexose isomerase Nucleotides Fatty Acids Fructose-6-Phosphate Catabolism
Don’t Eat the Toothpaste! • Phosphoglucomutase contains a PO4-2 group attached to residue D8. • Fluoride has a number of toxic effects • One of them is the removal of the phosphate from phosphoglucomutase • No phosphate = no activity • No activity = can’t utilize glycogen
Aldolase Reaction • The standard free energy , DGo,for the aldolase reaction is very unfavorable (~ +25 kJ/mol) • Under cellular conditions, the real free energy, DG, is favorable (~ -6 kJ/mol) • [G-3P] is maintained well below the equilibrium level by being processed through the glycolytic pathway
Phosphoglyceromutase H8 in human erythrocyte PGM
Overall Reaction The overall reaction of glycolysis is: Glucose + 2 NAD+ + 2 ADP + 2 Pi 2 pyruvate + 2 NADH + 2 ATP + 2 H2O + 4 H+ • There is a net gain of 2 ATP per glucose molecule • As glucose is oxidized, two NAD+ are reduced to 2 NADH