# 5: Fuel for Later


Learning objectives

Gluconeogenesis and glycogenolysis

1. Determine the regulatory states of the key gluconeogenic enzymes (fructose bisphosphatase 1 (FBP1), pyruvate carboxylase/PEPCK, glucose 6-phosphatase) under fed and fasting conditions.
2. Relate how gluconeogenesis, the urea cycle, and $$\beta$$-oxidation are interconnected and how defects in one of these pathways can result in the presentation of hypoglycemia.
3. Describe the process and regulation of glycogenolysis.
4. Compare the use of muscle and liver glycogen stores.

Lipolysis, $$\beta$$-oxidation, and ketogenesis

1. Describe the process of $$\beta$$-oxidation and how this connects to ketogenesis and lipolysis.
2. Describe the importance of carnitine in the movement of fatty acids into the mitochondria using carnitine palmitoyltransferase.
3. Evaluate the role of malonyl-CoA as a regulator of $$\beta$$-oxidation (key enzyme carnitine palmitoyltransferase 1).
4. Describe how hormone levels impact lipolysis through the regulation of hormone-sensitive lipase.

Urea cycle and nitrogen metabolism

1. Define ketogenic and glucogenic amino acids, and list them as exclusively ketogenic, glucogenic, or both.
2. Describe urea cycle regulation by N-acetyl glutamate (NAGS) and substrate availability.
3. Relate the activity of the urea cycle to the fed and fasted states.
4. Describe the interconversion between keto-acids and amino acids, including the requirement of pyridoxal phosphate (PLP) as a cofactor (transaminase reaction).
5. Describe the importance of the reactions catalyzed by (A) glutamine synthetase, (B) glutaminase, and (C) glutamate dehydrogenase.

Glycogenolysis (see section 4.5)

1. Contrast the regulation and the utility of skeletal muscle versus liver glycogen.
2. Evaluate the regulatory status of critical enzymes in the following pathways: glycolysis, glycogen synthesis and degradation, fatty acid synthesis and $$\beta$$-oxidation, and gluconeogenesis.
3. Determine how different storage disorders can present with alternative phenotypes.

In order to maintain glucose homeostasis, mechanisms are in place to supply fuel to essential tissues even under fasted conditions. This section will address how these pathways are interconnected and simultaneously regulated to achieve this goal.

Thumbnail: Grey, Kindred, Chapter 5. 2021. CC BY 4.0.

This page titled 5: Fuel for Later is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Renee J. LeClair (Virginia Tech Libraries' Open Education Initiative) .