Exam 16: The Citric Acid Cycle

Draw the citric acid cycle from isocitrate to fumarate only,showing and naming each intermediate.Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed,and name the enzyme that catalyzes each step.

The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP)by substrate level phosphorylation is the conversion of:

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates.Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids.What accounts for this difference?

In the citric acid cycle,a five-carbon compound is decarboxylated to yield an activated four-carbon compound.Show the substrate and product in this step,and indicate where any cofactor(s)participate(s).

Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD⁺ $\rightarrow$ oxaloacetate + NADH + H⁺ $\Delta$ G'° = +29.7 kJ/mol

Show the structures of the reactants and products for two of the four redox reactions in the citric acid cycle.Indicate where any cofactors participate,and label the reactants,products,and cofactors as oxidants or reductants in the reaction.

Which of the following is not true of the reaction catalyzed by the pyruvate dehydrogenase complex?

During the reaction of pyruvate carboxylase,CO₂ is covalently attached to all the following except:

The human disease beriberi is caused by a deficiency of thiamine in the diet.People with severe beriberi have higher than normal levels of pyruvate in their blood and urine.Explain this observation in terms of specific enzymatic reaction(s).

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA?

Which of the following is not true of the citric acid cycle?

The conversion of 1 mol of pyruvate to 3 mol of CO₂ via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH,_____ mol of FADH₂,and _____ mol of ATP (or GTP).

Show the reactions by which $\alpha$ -ketoglutarate is converted to malate in the citric acid cycle.

The standard reduction potentials (E'°)for the following half reactions are given. Fumarate + 2H⁺ + 2e^- $\rightarrow$ succinate E'° = +0.031 V FAD + 2H⁺ + 2e^- $\rightarrow$ FADH₂ E'° = -0.219 V If succinate,fumarate,FAD,and FADH₂,all at l M concentrations,were mixed together in the presence of succinate dehydrogenase,which of the following would happen initially?

Show the three reactions in the citric acid cycle in which NADH is produced,including the structures.None of these reactions involves molecular oxygen (O₂),but all three reactions are strongly inhibited by anaerobic conditions;explain why.

You are in charge of genetically engineering a new bacterium that will derive all of its ATP from sunlight by photosynthesis.Will you put the enzymes of the citric acid cycle in this organism? Briefly explain why or why not.

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.