Grossmont College Intermediary Metabolism Worksheet

Work out the following problems. You are encouraged to work in groups and you are welcome to ask for help from your instructor after you have first attempted the problems yourself.

• Write a balanced chemical reaction (reactants on the left, products on the right) for one molecule of glucose passing through glycolysis and the citric acid cycle to yield six molecules of CO2. Account for the net consumption and production of all other molecules (NAD+, ATP, H2O etc.)

• Write out each of the eight chemical reactions of the citric acid cycle. Draw the structures of the reactants and the products and name the enzymes of each reaction.

• Trace the course of the radioactive label in 2-[14C]glucose through glycolysis and the citric acid cycle. At what points(s) in the cycle will the radioactivity be released as 14CO2? How many turns of the cyle will be required for complete conversion of the radioactivity to CO2?

• Repeat problem 3 for pyruvate that is 14C-labeled at its methyl group.

• Aconitase catalyzes the citric acid cycle reaction:

citrate ⇌ isocitrate

The standard state Gibb’s Free Energy (ΔG°’) for this reaction is +6.7 kJ/mol. However, the observed free energy change (ΔG) for this reaction in pig heart mitochondia is +0.8 kJ/mol. What is the ratio of [isoctirate]/[citrate] in these mitochondria? If [isocitrate] = 0.3 mM, what is [citrate]? Use 25°C as your temperature.