1. Metabolic pathways Metabolism of ketone bodies involves several different pathways, such as the production of glucose (gluconeogenesis), the oxidation of fatty acid, and the citric acid cycle. All of these pathways are part of energy metabolism, which is composed of reactions involved in generating or storing metabolic energy. There are two major divisions in metabolism: 1. processes in which complex substances are degraded to simpler molecules accompanied by the net release of chemical energy and
2. processes concerned primarily with the synthesis of complex organic molecules, which requires a net input of chemical energy.
Some pathways, such as the citric acid cycle, can serve in both functions. Oxaloacetate is an important intermediate in several of these pathways, especially the citric acid cycle. Depleted oxaloacetate, just like other citric acid cycle intermediates, has to be replenished to maintain flux through the cycle. Separate metabolic pathways serve this purpose by balancing the flow of carbon in and out of the cycle. Define the major metabolic pathways by completing the sentences. Match the words in the left column to the appropriate blanks in the sentences on the right.
a. catabolic
b. anabolic
c. anaplerotic
d. amphibolic
1. A(n)process is the process in which complex biomolecules are built up from simpler.
2. Thepathway involves both catabolic and anabolic processes.
3. A(n)process is the process that replenishes the stores of citric acid cycle intermediates.
4. A(n)process is the process by which complex molecules are broken down to simpler ones.
2. Identify the reactants and products of the citrate synthase reaction in Step 1 of the citric acid cycle. Drag the appropriate participants to their respective bins.
a. acetyl-CoA
b. citrate
c. heat
d. CoA-SH
e. oxaloacetate
1. Reactants
2. Products
3. Neither
3. Mechanism for elevated ketone formation
After analyzing the role of oxaloacetate in the first step of the citric acid cycle and formation reactions of ketone bodies above, your research group proposed several possible mechanisms for increased ketone bodies levels when oxaloacetate is depleted. Based on the information about ketone body synthesis, predict which possibility is the most reasonable.
A. Another molecule (unknown at this point) reacts with available acetyl-CoA to form acetone, one of the ketone bodies.
B. Lack of oxaloacetate frees the enzyme, citrate synthase, to be diverted to catalyze the formation of the ketone bodies.
C. Oxaloacetate is unavailable to react with acetyl-CoA, resulting in acetyl-CoA being converted into acetoacetate, one of the ketone bodies.
D. Oxaloacetate is an inhibitor of the enzyme catalyzing ketone body formation, thiolase; a lack of oxaloacetate activates the enzyme and increases the production of the ketone bodies.
4. Replenish oxalate in animals
What enzyme catalyzes the reversible, biotin-dependent carboxylation of pyruvate to give oxaloacetate in animals?
a. pyruvate carboxylase.
b. phosphoenolpyruvate carboxylase.
c. malate dehydrogenase.
d. phosphoenolpyruvate carboxykinase.