Problem 18
What are the activated electron carriers for catabolism? For anabolism?
Problem 19
Thioesters, common in biochemistry, are more unstable (energy rich) than oxygen esters. Explain.
Problem 20
What are the three principal means of controlling metabolic reactions?
Problem 21
Glycolysis is a series of 10 linked reactions that convert one molecule of glucose into two molecules of pyruvate with the concomitant synthesis of two molecules of ATP (Chapter 16 ). The \(\Delta G^{\circ \prime}\) for this set of reactions is \(-35.6 \mathrm{kJ} \mathrm{mol}^{-1}\left(-8.5 \mathrm{kcal} \mathrm{mol}^{-1}\right),\) whereas the \(\Delta G^{\circ}\) is \(-90 \mathrm{kJ} \mathrm{mol}^{-1}\left(-22 \mathrm{kcal} \mathrm{mol}^{-1}\right) .\) Explain why the free-energy release is so much greater under intracellular conditions than under standard conditions.
Problem 23
Digestion is the first stage in the extraction of energy from food, but no useful energy is acquired in this stage. Why is digestion considered a stage in energy extraction?
Problem 24
The reaction of NADH with oxygen to produce \(\mathrm{NAD}^{+}\) and \(\mathrm{H}_{2} \mathrm{O}\) is very exergonic, yet the reaction of NADH and oxygen takes place very slowly. Why does a thermodynamically favorable reaction not take place rapidly?
Problem 25
The \(\mathrm{p} K_{\mathrm{a}}\) of an acid is a measure of its proton-group- transfer potential. (a) Derive a relation between \(\Delta G^{\circ \prime}\) and \(\mathrm{p} K_{\mathrm{a}}\) (b) What is the \(\Delta G^{\circ}\) ' for the ionization of acetic acid, which has a \(\mathrm{p} K_{\mathrm{a}}\) of \(4.8 ?\)
Problem 26
Fibrinogen, a precursor to the bloodclot protein fibrin, contains tyrosine-O- sulfate. Propose an activated form of sulfate that could react in vivo with the aromatic hydroxyl group of a tyrosine residue in a protein to form tyrosine-O-sulfate.
Problem 29
Creatine is a popular, but untested, dietary supplement. (a) What is the biochemical rationale for the use of creatine? (b) What type of exercise would most benefit from creatine supplementation?
Problem 30
The enzyme aldolase catalyzes the following reaction in the glycolytic pathway: Fructose \(1,6-\) bisphosphate \(\rightleftharpoons\) dihydroxyacetone phosphate \(+\) glyceraldehyde 3 -phosphate The \(\Delta G^{\circ \prime}\) for the reaction is \(+23.8 \mathrm{kJ} \mathrm{mol}^{-1}(+5.7 \mathrm{kcal}\) \(\left.\operatorname{mol}^{-1}\right),\) whereas the \(\Delta G^{\circ}\) in the cell is \(-1.3 \mathrm{kJ} \mathrm{mol}^{-1}\) \(\left(-0.3 \mathrm{kcal} \mathrm{mol}^{-1}\right) .\) Calculate the ratio of reactants to products under equilibrium and intracellular conditions. Using your results, explain how the reaction can be endergonic under standard conditions and exergonic under intracellular conditions.
