Flashcards in Biochemistry 1.6 Deck (21):
What fuels brain metabolism?
What is the significance of sufficiently low blood glucose?
How is glucose transported?
facilitated diffusion through GLUT transporters
How does glucose get trapped inside of a cell?
travel into cells down a concentration gradient without use of energy; cannot go against concentration gradient to leave
What is the GLUT receptor(s) of the liver?
Km = 300 mg/dL
What is the GLUT receptor(s) of adipose tissue?
Km = 90 mg/dL
What is the GLUT receptor(s) of muscle?
Km = 90 mg/dL
What is the GLUT receptor(s) of the brain?
Km = 20 mg/dL
What is Km?
Michaelis constant of an enzyme; indicates the concentration of a substrate which is sufficient for the rate of catalysis to be half of the maximum rate of catalysis
What are astrocytes?
the workhorse cells of the brain, play many roles to support neurons.
Astrocytes absorb glucose directly through the BBB, to make glycogen as an energy buffer for neurons
What is the role of glycogen phosphorylase in astrocytes?
hydrolyze glycogen to glucose-6-phosphate
Why don't astrocytes release glucose directly, but instead oxidize glucose to lactate?
No glucose-6-phosphatase activity
Which type of metabolism acts in astrocytes?
Which type of metabolism acts in neurons?
What is the order of brain metabolism of glucose?
1) anaerobic metabolism of glucose to lactate in astrocytes
2) aerobic metabolism of lactate in neurons
What can the brain do to compensate during brain starvation?
supplement its fuel supply by substituting ketone bodies for glucose (acetoacetate and D-b-hydroxybutarate)
How can the brain use fat?
-cannot burn fat
-fat cannot be converted to glucose
-fat CAN yield fuel and for 2-C skeletons to produce ketone bodies (soluble in the blood)
Where are fatty acids released and converted into ketones?
from adipose tissue to *liver* to brain
When fatty acid is oxidized to acetyl-CoA by the liver, why is the product not directly sent to the brain?
When in the blood stream, Acetyl-CoA would be altered by other enzymes; actual ketone bodies are de-protonated and soluble in the blood and BBB
What is 90% of the fat in the body stored as?
triglycerols; lipase converts to glycerol + free fatty acids