METABOLISM HOMEWORK
You must indicate how you arrived at your answers with full structures if required in obtaining the answer.
CHEM 4253
1. Write balanced equations for the following processes, including all associated phosphorylation steps.
(a) Conversion of glycerol to lactic acid
(b) Fermentation of sucrose to ethanol and CO2
2. A yeast extract containing all the enzymes required in the alcoholic fermentation of glucose is incubated with 200
mM D-glucose, 400 mM ADP, traces of ATP and NAD+, and 20 mM phosphate. The incubation is continued
until the system comes to equilibrium.
(a) Predict the concentration of glucose and the concentration of ethanol at equilibrium.
(b) How can the fermentation be made to go to completion so that essentially all the glucose is converted into ethanol?
3. (a) Calculate the overall free-energy change when glycolysis occurs under the following set of conditions, which are
similar to those existing in the intact cell: glucose = 5 mM, phosphate = 1.0 mM, ADP = 0.5 mM, ATP = 3.0
mM, and lactate = 3.0 mM.
(b) What will the free-energy change be when the lactate concentration is raised to 100 mM?
4. The concentration of fructose-1,6-diphosphate in the intracellular fluid of cerebral cortex tissue is 0.146 mM while
the total concentration of the two triose phosphates is 0.0942 mM. Calculate the free-energy change at 25oC for
the aldolase reaction under these conditions, assuming the reaction catalyzed by triose phosphate isomerase to
be at equilibrium.
5. A soluble muscle extract capable of lactate fermentation from fructose is prepared. Fructose labeled at C-2 with 14C
is added to the system. Outline this pathway and locate the labeled atoms after fermentation is complete.
(Include all cofactors and use structures when required to follow the labeled positions.)
6. List two enzymes from Glycolysis which represent control points. Briefly describe the control rational. (i.e. what
positive and negative effectors are used and why?)
7. Why is glycerol considered an aerobic energy source? Provide the reactions in your answer which demonstrate this
dependency.
8. How many net ATP's can be obtained from the catabolism of glucose via anaerobic metabolism? Give the specific
steps in glycolysis to show how this number is determined.
P.S. Answer these questions on separate pages. You will need to be working on these questions as we complete the
information in class which will permit you to answer them.