Neurochemistry Flashcards
List catecholamine derivatives of tyrosine.
(a) Dopamine
(b) Epinephrine
(c) Norepinephrine
Further notes:
Catecholamines are a class of aromatic amines that function as both hormones and neurotransmitters.
List two neurotransmitter derivatives of tryptophan.
serotonin [5-hydroxytryptophan]
melatonin [N-Acetyl-5-methoxytryptamine]
Name the neurotransmitter derivative of glutamate.
Gamma-aminobutyric acid [GABA]
Name four amino acids which act as neurotransmitters.
glutamate, glycine, aspartate, serine
What are the three main sources of energy for the brain (in order of metabolic significance)?
(1) Glucose: main energy source for the brain
(2) Ketone bodies: e.g. beta-hydroxybutyrate and acetoacetate. These are utilized during periods of low glucose availability, such as fasting or prolonged exercise.
(3) Lactate
List three inhibitory and three excitatory neurotransmitters.
Excitatory: glutamate, acetylcholine, norepinephrine
Inhibitory: GABA, glycine, serotonin
Explain how GABA and Glycine cause their inhibitory effect.
🧬 GABA and glycine bind to their respective receptors (GABA-A and glycine receptors).
🧬 These receptors are ligand-gated ion channels that, when activated, allow the influx of negatively charged chloride ions (Cl⁻) into the neuron.
🧬 The influx of Cl⁻ makes the inside of the neuron more negative (hyperpolarized), moving the membrane potential further from the threshold needed to trigger an action potential.
How is GABA synthesized in the brain?
GABA is synthesized from glutamate by the enzyme glutamate decarboxylase [for which PLP is a coenzyme] in GABAergic neurons.
How is GABA metabolized in astrocytes?
What are the two main types of GABA receptors and their functions?
The two main types of GABA receptors are GABA-A (ionotropic, fast-acting, chloride ion channels) and GABA-B (metabotropic, slower-acting, G-protein-coupled receptors).
Briefly discuss the synthesis of dopamine, norepinephrine and epinephrine from tyrosine.
Start here:
Tyrosine ⇒ L-DOPA ⇒ Dopamine ⇒ Norepinephrine ⇒ Epinephrine
Then dig the details … [if you have time]
(1) Tyrosine to L-DOPA
Reaction: Tyrosine is hydroxylated to form to L-DOPA (L-3,4-dihydroxyphenylalanine)
Enzyme: Tyrosine hydroxylase
Cofactor: TH4 (Tetrahydrobiopterin)
This is the rate-limiting step in the synthesis of all catecholamines.
(2) L-DOPA to Dopamine
Reaction: L-DOPA is decarboxylated to form dopamine.
Enzyme: DOPA decarboxylase (also known as aromatic L-amino acid decarboxylase, AADC)
Cofactor: Pyridoxal phosphate (PLP), the active form of vitamin B6
(3) Dopamine to Norepinephrine
Reaction: Dopamine is hydroxylated to form norepinephrine.
Enzyme: Dopamine β-hydroxylase (DBH)
Cofactor: Ascorbate (vitamin C) and copper ions (Cu(^2+))14
(4) Norepinephrine to Epinephrine
Reaction: Norepinephrine is methylated to form epinephrine.
Enzyme: Phenylethanolamine N-methyltransferase (PNMT)
Cofactor: S-adenosylmethionine (SAM) serves as the methyl donor
List the vitamins involved in catecholamine synthesis.
Vitamin B6, Vitamin C, Cobalamin (B12), Folate (B9)
(a) Write an equation for the formation of acetylcholine.
(b) Name the enzyme that participates in this reaction.
(a) Choline + Acetyl CoA ⇒ Acetylcholine + Coenzyme A
(b) Choline Acetyltransferase (ChAT)
Briefly discuss the degradation of acetylcholine.
acetylcholine ⇒ choline + acetate
Enzyme: acetlycholinesterase
Briefly discuss the synthesis of serotonin aka. 5-hydroxytryptamine (5-HT).
tryptophan ⇒ 5-hydroxytryptophan ⇒ 5-hydroxytryptamine
(1) Hydroxylation: The enzyme tryptophan hydroxylase (TPH) converts tryptophan into 5-hydroxytryptophan (5-HTP). This is the rate-limiting step in serotonin synthesis.
(2) Decarboxylation: The enzyme aromatic L-amino acid decarboxylase (AAAD) then converts 5-HTP into serotonin (5-HT).
