Brain Metabolism

  1. What is the primary source of fuel for the brain?
  2. Why is brain metabolism mostly aerobic?
    Brain uses 20% of the body’s ATP so must generate a lot of ATP
  3. What does the brain do with all the energy it uses?
    80% of ATP used by brain powers formation and maintenance of ionic gradients (Na+/K+ pump)
  4. How does glucose get into the brain?
    Facilitated diffusion via GLUT transporters
  5. An enzyme with a high Km has a __________________ affinity for substrate
  6. An enzyme with a low Km has a __________________ affinity for substrate
  7. What does Km indicate?
    The concentration of substrate which is enough for the rate of catalysis to be half of the maximum rate of catalysis
  8. GLUT2 is located in ____________________ and has a Km value of _____________
    • Liver
    • 300 mg/dl
  9. GLUT4 is located in ___________________ and has a Km value of _____________
    • Adipose tissue and muscle
    • 90 mg/dl
  10. GLUT1 is located in ___________________ and has a Km value of _____________
    • BBB
    • 20 mg/dl
  11. GLUT3 is located in ___________________ and has a Km value of _____________
    • Neurons
    • 10 mg/dl in neurons
  12. What is the blood brain barrier?
    Endothelial cells that cover the entire capillary system of the brain that restricts what can enter the brain
  13. Glucose must pass through ___________ transporter before it can pass through _____________ transporter
    • GLUT1 (BBB)
    • GLUT3 (neurons)
  14. Which can transport glucose faster, BBB or neurons? Why?
    • Neurons, because they have a lower Km than BBB
    • GLUT1 Km = 20 mg/dl
    • GLUT3 Km = 10 mg/dl
  15. What is the role of astrocytes in the brain?
    Absorb glucose directly through the BBB to make glycogen
  16. What is the process of astrocytes feeding neurons?
    • 1. Take glucose through BBB
    • 2. Turn glucose into glycogen
    • 3. Glycogen converted to glucose when needed
    • 4. Glucose turned into lactate
    • 5. Lactate fed to neurons
  17. When needed, _____________________ in astrocytes hydrolyze glycogen to glucose-6-phsophate
    Glycogen phosphorylase
  18. Why must astrocytes use lactate as fuel instead of glucose?
    Only liver and kidney cells have glucose-6-phosphatase
  19. How do astrocytes and neurons work in conjunction during metabolism?
    • Astrocytes do anaerobic metabolism to create lactate and send the lactate to the neuron
    • Neurons do aerobic metabolism using the lactate
  20. __________________ is normally the sole source of fuel for the brain, but during starvation the brain can supplement its fuel supply by using ____________________
    Ketone bodies
  21. The liver produces which ketone bodies? Which of these can the brain catabolize?
    Acetone, acetoacetate, D-β-hydroxybutarate
  22. Why is D-β-hydroxybutarate different than acetone and acetoacetate?
    D-β-hydroxybutarate does not have a ketone
  23. Energy from ketone bodies is stored as ____________________
  24. Can the brain use fat as fuel?
    Brain can’t burn fat or convert fat to glucose, but you can get two-carbon skeletons from fat and then make ketone bodies
  25. 90% of fat in the body is stored in the form of ____________________
  26. Triacylglycerols are hydrolyzed into ______________ and ________________ which can be exported through the membrane of the fat cell
    • Glycerol
    • Free fatty acids
  27. β-oxidation of fatty acids in hepatocytes produces _____________________, which in turn will be used to produce ketone bodies
    Acetyl-coenzyme A
  28. The liver uses _________________ to form carbon-carbon bonds of ketone bodies
    Thioester bonds
  29. Explain why fasting leads to a buildup of ketone bodies
    When you fast you start burning fat and that creates ketone bodies

    • What is 3-hydroxy-3-methyl glutaryl CoA?
    • A precursor used to make ketone bodies or cholesterol
  30. What is the function of HMG-CoA reductase?
    Reduces 3-hydroxy-3-methyl glutaryl CoA into mevalonate
  31. What is the function of HMG-CoA lyase?
    Lyses 3-hydroxy-3methyl glutaryl CoA leading to ketone body synthesis
Card Set
Brain Metabolism