Synthesis And Removal Of Amino Acid Toansmitters

Question 1

What is the purpose of the krebs cycle?

Answer 1

Synthetic Pathway 1
• Kreb’s cycle
1. Glucose enters neuron by facilitated diffusion
2. Intracellular glucose metabolized via Krebs cycle
3. Alpha-oxoglutarate transaminase yields glutamate

Question 2

Describe glutamate recycling

Answer 2

Synthetic Pathway 2
• Glutamate recycling
1. Terminal and astrocytic glutamate transporters
take up extracellular glutamate
2. Glutamine synthetase metabolizes glutamate to form glutamine in astrocytes
3. Glutamine exits astrocytes and enters neurons through glutamine transporters
4. Intraneuronal glutaminase converts glutamine to glutamate for reloading into vesicles
5. Glutamate taken up by neuronal terminals is also subject to vesicular reloading

Question 3

Describe the synthesis and removal of GABA

Answer 3

Synthesis and removal
1. Glutaminase converts glutamine to
glutamate
2. Glutamic acid decarboxylase converts
glutamate to GABA*
3. GABA enters vesicles
4. After release, GABA transporters take up GABA for reuse
5. Glia take up GABA, where GABA transaminase degrades GABA to form glutamate
6. Glutamine synthetase then converts glutamate to glutamine
7. Glutamine return to neurons for re- synthesis of glutamate then GABA

Question 4

Describe the synthesis and removal of Glycine

Answer 4

Synthesis and removal

1. Glycolysis of glucose yields 3- phosphoglycerate and subsequently serine
2. Serine transhydroxymethylase folate- dependently converts serine to glycine
3. Membrane-spanning transporters take up synaptic glycine

Question 5

Describe the synthesis and removal lf acetylcholine

Answer 5

1. Glucose enters cell through facilitated diffusion
2. Cytoplasmic glycolysis generates pyruvate
3. Pyruvate enters mitochondria
4. Donates acetyl group to coenzyme-A
5. Acetyl coenzyme-A returns to cytoplasm
6. *Choline retrieved from the synapse interacts with acetyl coenzyme-A in presence of ACh transferase to yield ACh
7. ACh enters vesicles
8. ACh esterase hydrolyzes ACh (resultant choline taken up for re- use)

Question 6

What is the impact of choline concentration on ACh synthesis?

Answer 6

Choline is present in plasma. Acetylcholine (Ach) formation is limited by the intracellular concentration of choline, which is determined by uptake of choline into the nerve ending