Problem 1
They are everywhere. What energetic barrier prevents glycolysis from simply running in reverse to synthesize glucose? What is the energetic cost of overcoming this barrier?
Problem 3
What reactions of glycolysis are not reversible under intracellular conditions? How are these reactions bypassed in gluconeogenesis?
Problem 4
Avidin, a 70 -kDa protein in egg white, has very high affinity for biotin. In fact, it is a highly specific inhibitor of biotin enzymes. Which of the following conversions would be blocked by the addition of avidin to a cell homogenate? (a) Glucose \(\rightarrow\) pyruvate (b) Pyruvate \(\rightarrow\) glucose (c) Oxaloacetate \(\rightarrow\) glucose (d) Malate \(\rightarrow\) oxaloacetate (e) Pyruvate \(\rightarrow\) oxaloacetate (f) Glyceraldehyde 3 -phosphate \(\rightarrow\) fructose 1,6 -bisphosphate
Problem 5
Gluconeogenesis takes place during intense exercise, which seems counterintuitive. Why would an organism synthesize glucose and, at the same time, use glucose to generate energy?
Problem 6
Liver is primarily a gluconeogenic tissue, whereas muscle is primarily glycolytic. Why does this division of labor make good physiological sense?
Problem 7
What would be the effect on an organism's ability to use glucose as an energy source if a mutation inactivated glucose 6 -phosphatase in the liver?
Problem 8
Why does the lack of glucose 6 -phosphatase activity in the brain and muscle make good physiological sense?
Problem 9
Compare the roles of lactate dehydrogenase in gluconeogenesis and in lactic acid fermentation.
Problem 11
In starvation, protein degradation takes place in muscle. Explain how this degradation might affect gluconeogenesis in the liver.
Problem 14
What are the two potential substrate cycles in the glycolytic and gluconeogenic pathways?
