2.12 Biochem Glutamate

Question 1

What’s this? what’s it do?

Answer 1

• glutamate. most prevalent excitatory NT in body
• Glutamate, glutamine, and a-ketoglutarate interconvert

thereby supporting essential processes including: brain metabolism, neurotransmitter recycling, the urea cycle, ammonium detoxification, amino acid metabolism, and nucleotide biosynthesis

Question 2

What’s this?

Answer 2

glutamine = the most prevalent amino acid in gluten about ¼ of all amino acid

-Glutamate, glutamine, and a-ketoglutarate interconvert

thereby supporting essential processes including: brain metabolism, neurotransmitter recycling, the urea cycle, ammonium detoxification, amino acid metabolism, and nucleotide biosynthesis

Question 3

What’s this?

Answer 3

• a-ketoglutarate = a five carbon a-keto acid that has a carboxylic acid side chain
• Glutamate, glutamine, and a-ketoglutarate interconvert

thereby supporting essential processes including: brain metabolism, neurotransmitter recycling, the urea cycle, ammonium detoxification, amino acid metabolism, and nucleotide biosynthesis.

Question 4

Which catalyzes RXN glutamine to glutamate?

Glutamate to glutamine?

Answer 4

Question 5

which enzyme catalyzes RXN glumatate -> a-ketogluterate?

a-ketogluterate -> glutamate?

Answer 5

Question 6

Which reactions are spontaneous (which reactions lead to decreased energy)?

Which reactions require an input of energy?

Answer 6

1. Glutamate is a breakdown product of glutamine because glutamine is higher in energy.
2. Glutamine’s single bond to nitrogen is replaced by two bonds to oxygen in forming glutamate.
3. Glutamate is more oxidized and lower in energy than glutamine.
4. Therefore, glutamine synthetase requires energy to convert glutamate to glutamine.

Question 7

Explain why astroytes cannot directly release glucose to make it available for neurons.

Answer 7

recall that, in astrocytes, hexokinase phosphorylates glucose to G-6-P. But astrocytes don’t have G-6 Phosphatase to cleave the phosphate group –> soooo the G-6-P is stuck inside astrocyte. astrocyte can make glycogen though!

Question 8

Diagram the pathway by which astrocytes are able to use stores of glycogen in order to provide fuel for neurons.

Answer 8

recall:

Question 9

where is the glutamin-glutamate cycle occuring? which parts occur in which cells? be able to diagram and explain this.

That’s kinda weird, right? why do it this way?

Answer 9

1. Glutamate left over in the synapse is ferried away with Na+ to inside astrocyte (via EAAT). 2. then glutamte –> glutamine with glutamine synthetase 3. then glutamine exported from astrocyte to inside presynaptic neuron where…4. glutamine –>glutamate with gluatminase
2. glutamate changed to glutamine before export because too much glutamate floating around extracellularly is bad

Question 10

What do the Excitatory Amino Acid Transporters do ? Why?

Answer 10

1. Excitatory Amino Acid Transporters actively transport glutamate out of the extracellular space with Na+ ion as chaparone (this uses ATP because glutamate is moving against its gradient)
2. This keeps the extracellular glutamate concentration low. Too much extracellular glutamate is muy mal (–>seizures, neuronal death)

Question 11

what do you know about glutamine synthetase? Which cell contains more of this enzyme? RXN sponaneous?

Answer 11

1. makes glutamine 2. not sponaneous - product is reduced 3. more in the astrocytes

Question 12

what do you know about glutaminase? Which cell contains more of this enzyme?

Answer 12

1. makes glutamate 2. RXN is sponaneous - product is oxidized 3. more in presynaptic neuron

Question 13

Besides glutamate –> glutamine, what other RXN is occuring in the astrocyte? Where does the product of this RXN go?

Answer 13

1. a-ketogluterate goes to fuel energy production. a-ketogluterate is oxidized. 2. if body needs more energy, a-ketogluterate is produced here and it heads on over to citric acid cycle to help make energy