Biochemistry 1.6

Question 1

What fuels brain metabolism?

Answer 1

glucose

Question 2

What is the significance of sufficiently low blood glucose?

Answer 2

brain death

Question 3

How is glucose transported?

Answer 3

facilitated diffusion through GLUT transporters

Question 4

How does glucose get trapped inside of a cell?

Answer 4

travel into cells down a concentration gradient without use of energy; cannot go against concentration gradient to leave

Question 5

What is the GLUT receptor(s) of the liver?

Answer 5

GLUT2

Km = 300 mg/dL

Question 6

What is the GLUT receptor(s) of adipose tissue?

Answer 6

GLUT4

Km = 90 mg/dL

Question 7

What is the GLUT receptor(s) of muscle?

Answer 7

GLUT4

Km = 90 mg/dL

Question 8

What is the GLUT receptor(s) of the brain?

Answer 8

GLUT1
GLUT3

Km = 20 mg/dL

Question 9

What is Km?

Answer 9

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

Question 10

What are astrocytes?

Answer 10

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

Question 11

What is the role of glycogen phosphorylase in astrocytes?

Answer 11

hydrolyze glycogen to glucose-6-phosphate

Question 12

Why don’t astrocytes release glucose directly, but instead oxidize glucose to lactate?

Answer 12

No glucose-6-phosphatase activity

Question 13

Which type of metabolism acts in astrocytes?

Answer 13

anaerobic

Question 14

Which type of metabolism acts in neurons?

Answer 14

aerobic

Question 15

What is the order of brain metabolism of glucose?

Answer 15

1) anaerobic metabolism of glucose to lactate in astrocytes

2) aerobic metabolism of lactate in neurons

Question 16

What can the brain do to compensate during brain starvation?

Answer 16

supplement its fuel supply by substituting ketone bodies for glucose (acetoacetate and D-b-hydroxybutarate)

Question 17

How can the brain use fat?

Answer 17

• 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)

Question 18

Where are fatty acids released and converted into ketones?

Answer 18

from adipose tissue to liver to brain

Question 19

When fatty acid is oxidized to acetyl-CoA by the liver, why is the product not directly sent to the brain?

Answer 19

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

Question 20

What is 90% of the fat in the body stored as?

Answer 20

triglycerols; lipase converts to glycerol + free fatty acids

Question 21

What is the precursor to cholesterol?

Answer 21

3-hydroxy-3-methyl glutaryl CoA (C-C bonds)