1. BIOC/DENT/PHCY 230 LECTURE 11

2. o glucose requirements:160g/day whole body (120g/day brain) o glucose reserves:190g glycogen 20g in body fluids o need to synthesise glucose during prolonged periods of fasting How long will glucose reserves last?

4. o synthesis of glucose from a variety of non-carbohydrate metabolites o lactate, glycerol and the carbon skeletons of certain amino acids can all be used as substrates (propionyl-CoA can also be used) Gluconeogenesis

5. hexokinase phosphofructokinase (PFK) pyruvate kinase o most of the reactions of gluconeogenesis are simply the reverse of the corresponding steps in glycolysis o however those reactions which represent irreversible steps in glycolysis need to be by-passed

6. By-passing pyruvate kinase Converting pyruvate back to phosphoenolpyruvate (PEP) is a two step process Reaction 1: pyruvate + CO 2 + H 2 O + ATP oxaloacetate + ADP + P i + 2H + o catalysed by pyruvate carboxylase o mitochondrial reaction o oxaloacetate transported out of mitochondria as malate o allosterically activated by acetyl-CoA

7. o there is no mitochondrial transporter for oxaloacetate o oxaloacetate is converted to malate which can be transported out of the mitochondria o the reverse reaction occurs in the cytoplasm

8. oxaloacetate + GTPPEP + CO 2 + GDP   G’ = -25kJ/mol for the combined reactions o catalysed by phosphoenolpyruvate carboxykinase (PEPCK) o synthesis of PEPCK is stimulated by glucagon Reaction 2:

9. By-passing phosphofructokinase fructose-1,6-bisphosphate + H 2 Ofructose-6-P + P i   G 0 ’ = -16.3kJ/mol o catalysed by fructose-1,6-bisphosphatase o allosterically inhibited by fructose-2,6-BP and AMP

10. P PFK-2 PFK-1 [F-2,6-BP] increases as [F-6-P] increases

11. Glucose Glucose-6-P Fructose-6-P hexokinase PFK - Fructose-1,6-BP Fructose-2,6-BP +

12. By-passing glucokinase Glucose-6-phosphate + H 2 Oglucose + P i   G 0 ’ = -12.1kJ/mol o catalysed by glucose-6-phosphatase o most tissues lack this enzyme o primarily expressed in liver o allows liver to release glucose into the bloodstream

13. A comparison of energy input and output from glycolysis and gluconeogenesis Whilst the  G’ for both glycolysis and gluconeogenesis is negative, gluconeogenesis is a net consumer of energy

14. Entry points into gluconeogensis amino acidslactate glycerol

15. lactate

16. amino acids

17. TAG DAG glycerol glycerol-3-phosphate DHAP glycerol kinase G-3-P DHase NAD +

19. Ketone Bodies o ketone bodies are synthesised from acetyl-CoA o they represent a means of using the energy available in fatty acids for tissues that may not be able to use fatty acids themselves o particularly important for the brain, as water soluble ketone bodies can cross the blood-brain barrier o help supplement the energy requirements of brain, which may not be met solely by glucose during prolonged fasting

22. Synthesis of ketone bodies o occurs primarily in liver mitochondria

23. Degradation of ketone bodies o in mitochondria of target tissues

24. Ketoacidosis

25. What do I need to study for the final exam? You do not: o need to memorise pathways o need to memorise structures o need to learn the names of all the intermediates and enzymes involved in the various pathways o need to understand the regulation mechanism for glycogen phosphorylase o know which specific amino acids are glucogenic and which are ketogenic

26. You do not: o need know equations for whole pathways o reaction mechanisms

27. You do need to know: o the logic of pathways eg.Why does flux through glycolysis decrease in the presence of oxygen? What is the significance of the LDH isozymes and the reactions they catalyse? Why is  -oxidation a cyclic series of reactions? o how pathways are regulated and linked eg. What are the regulatory steps of pathways? What are the key enzymes and how are they regulated?

28. Is the pathway regulated by substrate supply or subcellular location? Is there hormonal regulation of the pathway? Are the products of one pathway used in another? o how is metabolism integrated between tissues eg. How are muscle and liver metabolism linked? How are liver and brain metabolism linked? What effect does any given hormone have on various tissues?

29. o be able to describe the metabolism of the fed and fasted state How are these states regulated by hormones? What are the features of fuel synthesis and degradation that characterise each state? How do tissues co-operate in these states? How are pathways that carry out opposite sets of reactions reciprocally regulated? LOGIC/INTEGRATION/REGULATION