Biochemistry 2.12

Question 1

The fraction of neurons in the CNS that are signaled by the neurotransmitter glutamate is closest to ____%

Answer 1

100

Question 2

What is glutamate?

Answer 2

primary excitatory neurotransmitter of the CNS

Question 3

How is such an extreme glutamate concentration maintained in the brain?

Answer 3

glutamate transporters (excitatory amino acid transporter) w/ active transport pump glutamate into the cell

Question 4

How is the glutamate gradient affected by ischemia?

Answer 4

-Low ATP leads to decreased activity of Na+/ATPase pumps
-Loss of Na+ gradient disables active transport of glutamate.
-Leaking of glutamate leads to high extracellular glutamate causing
excess signaling, seizures, and neuronal cell death

Question 5

How is low extracellular glucose maintained?

Answer 5

glutamate-glutamine cycle

Question 6

What is glutaminase and where does it act?

Answer 6

• converts glutamine to glutamate (spontaneous)

- presynaptic neuron

Question 7

What is glutamine synthetase and where does if act?

Answer 7

• converts glutamate to glutamine (requires energy)

- astrocyte

Question 8

Glutamate and Glutamine: oxidized or reduced?

high or low energy?

Answer 8

Glutamate:
oxidized
low energy

Glutamine:
reduced
high energy

Question 9

Alternatively, what is glutamate converted to and for what purpose?

Answer 9

alpha-ketoglutarate

metabolism

Question 10

What replenishes
citric acid cycle
intermediates in the brain?

Answer 10

• glucose in the brain

- glutamtate can also be readily be converted to alpha-ketoglutarate