CARBOHYDRATE BIOSYNTHESIS

1. BC368 Biochemistry of the Cell II CARBOHYDRATE BIOSYNTHESIS April 15, 2014

2. ANABOLISM VS. CATABOLISM • Anabolic and catabolic pathways share many of the same reactions, but irreversible reactions are bypassed.

3. ANABOLISM VS. CATABOLISM • Anabolic and catabolic pathways undergo coordinate control. • Anabolic and catabolic pathways share many of the same reactions, but irreversible reactions are bypassed. • ATP hydrolysis drives biosynthetic processes even when precursor concentrations are low. • Example of anabolic pathway = gluconeogenesis, the synthesis of glucose from non-carbohydrate precursors, which helps to maintain glucose homeostasis.

4. Glucose Homeostasis • Normally, blood sugar is kept fairly constant by the liver. Blood sugar rises after food consumption (postprandial period)

5. Glucose Homeostasis • First line of defense against a fall in blood sugar is glycogen breakdown. Glycogen stores are depleted after an overnight fast

6. Glucose Homeostasis • Gluconeogenesis becomes significant after about 10 hours of fasting (or during exercise to process lactate).

7. Glucose Homeostasis • Hypoglycemia can result from fasting coupled with hard work.

8. ~Fig 14-16 Central role of oxalo- acetate in gluconeogenesis • Anything that can undergo net conversion to oxaloacetate can result in glucose. Lactic acid Glycerol • Note that acetyl-CoA does NOT result in glucose.

9. ΔG = -16 kJ/mol Fig 14-17 Gluconeo- genesis vs.glycolysis ΔG = -70 kJ/mol

10. Fig 14-17 Bypass #1

11. Fig 14-18 Pyruvate carboxylase rxn Acetyl-CoA is a positive effector

12. Fig 14-20 Transport as malate

13. Fig 14-18 PEP carboxykinase rxn

14. Bypass II: FBPase-1 rxn

15. Bypass III: glucose 6-phosphatase rxn

16. Lactate entry Gerty & Carl Cori

17. Lactate entry Gerty & Carl Cori

18. Lactate entry • Lactate entry requires a relatively high NAD+/NADH ratio in the cytosol. • No need to go through malate because reducing equivalents are formed in cytosol by LDH.

19. Case Study Emily, against her better judgment, agrees to run a 10K with her friend. She hasn’t really trained for the race, and her legs feel quite tired and heavy when she is done. Afterwards, her friend suggests that they go out for a few beers before heading back to campus. What does Emily tell her?

20. (OA) (OA) (OA)

21. Some animals are highly dependent on gluconeogenesis.

22. Reciprocal Regulation • Glycolysis activators inhibit gluconeogenesis. • Energy charge is key. • Low energy charge (high AMP, ADP) favors glycolysis. • High energy charge (high ATP) favors gluconeogenesis.

23. Pyruvate Carboxylase Regulation • Acetyl-CoA activates. Fig 15-22

24. FBPase-1/PFK-1 reciprical control Fig 15-18

25. Fig 15-18 Regulation by F26BP • F26BP inhibits FBPase-1 • F26BP stimulates PFK-1

26. Origin of F26BP • Single protein with two domains. • Activity of PFK-2/FBPase-2 is under complex hormonal control

27. Fig 15-19 Regulation of [F26BP]

28. Case Study You are a first-year resident called to the post-anesthesia care unit by a nurse who is concerned about a patient she just received from the operating room. The anesthesiologists and surgeons are all busy in the operating rooms due to the recent arrival of multiple trauma patients, so you need to deal with this problem on your own. The nurse tells you that shortly after arriving in the post-anesthesia care unit, the patient's blood pressure and heart rate began to rise. His temperature is also rising and is currently 40°C. According to the most recent arterial blood gas reading, the patient is acidotic with elevated CO2. Because you are stumped by these symptoms, the nurse gently informs you that she believes the patient may have malignant hyperthermia, a life-threatening syndrome that occurs during or immediately after general anesthesia. Along with considering how to treat the condition, you wonder what caused the condition to develop. What is the origin of the patient’s increased body temperature?

29. Malignant Hyperthermia • Malignant hyperthermia is genetic disorder that causes a rapid increase in body temperature and muscle rigidity when the patient is given general anesthesia. • Symptoms result from a hypercatabolic state because of a mutation in a calcium channel of muscle. The channel opens when bound by certain anesthetics, causing an influx of Ca2+. • Heat results from the following reactions. PFK-1 FBPase-1

30. In-Class Problem Consider a substrate cycle operating with enzymes X and Y in this pathway: • Under intracellular conditions, the activity of enzyme X is 100 pmol/106 cells/s and that of enzyme Y is 90 pmol/106 cells/s. What are the direction and rate of metabolic flux between B and C? • Calculate the effect of metabolic flux rate and direction after each of the following: • Adding an activator that increases the activity of X by 20% • Adding an inhibitor that decreases the activity of Y by 20% • Adding both the activator and the inhibitor

31. BC 368 Biochemistry of the Cell II CARBOHYDRATE BIOSYNTHESIS II April 17, 2014

32. Glycogen synthesis overview Glucose-6-phosphate phosphoglucomutase UDP-glucose pyrophosphorylase

33. Starting material = G 6-P Phosphoglucomutase

34. UDP-glucose

35. Fig 15-31 UDP-glucose

36. Fig 15-32 Glycogen synthase rxn

37. Fig 15-33 Branching enzyme

39. Fig 15-35 Glycogenin

40. Fig 15-35 Glycogenin

41. Fig 15-39 Regulation via phosphorylation

42. Fig 15-39 Regulation via phosphorylation

43. Fig 15-43 Hormone effects