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-hydroxytryptamine]
melatonin [N-Acetyl-5-methoxytryptamine]
Name the neurotransmitter derivative of glutamate.
Gamma-aminobutyric acid [GABA]
Name three amino acids which act as neurotransmitters.
glutamate, glycine, aspartate
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. [Diagram]
How is GABA metabolized in astrocytes?
What are the two main types of GABA receptors?
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 (Cu2+)
(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 + H2O
(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).
NO synthesis
(a) What is the starting substrate for the synthesis of nitric oxide?
(b) Which enzyme catalyzes the synthesis of nitric oxide (NO)?
(c) What are the products of the reaction catalyzed by nitric oxide synthase (NOS)?
(d) List non-substrate requirements in the synthesis of NO.
(a) starting substrate: L-arginine
(b) enzyme: Nitric oxide synthase (NOS)
(c) products: L-citrulline and nitric oxide (NO)
(d) important non-substrates: O2, NADPH, FAD, FMN, BH4, Calmodulin, Heme
Tetrahydrobiopterin (BH4) is a reductant involved in all the following except
(a) Melatonin synthesis
(b) Nitric oxide synthesis
(c) Serotonin synthesis
(d) GABA synthesis
(e) Phenylalanine degradation
(d) GABA synthesis
________ is not linked to ion channels.
(a) GABA
(b) Glycine
(c) Acetylcholine
(d) Serotonin
(e) Glutamate
(d) Serotonin
Explanation:
◾ Most serotonin receptors are G protein-coupled receptors (they trigger intracellular signaling cascades).
◾ There is however one sub-type of serotonin receptors that is a ligand-gated ion channel: the 5-HT3 receptor.
The following are all inhibitory neurotransmitters except ________.
(a) GABA
(b) norepinephrine
(c) glutamate
(d) serotonin
(e) glycine
(c) glutamate
Explanation:
While norepinephrine can have excitatory effects in some areas, norepinephrine is generally considered an inhibitory neurotransmitter, particularly in its role in regulating mood, sleep and arousal. Its effects can vary depending on the receptor it binds to and the brain region.
Which of the following neurotransmitters is inhibited by penicillin?
(a) GABA
(b) epinephrine
(c) norepinephrine
(d) serotonin
(e) aspartate
(a) GABA
Malfunctioning of dopamine may be associated with ________.
(a) Down’s syndrome
(b) Schizophrenia
(c) Parkinson’s disease
(d) Von Gierkes disease
(e) amnesia
(c) Parkinson’s disease
The abbreviation 5-HT stands for ________.
(a) acetylcholine
(b) dopamine
(c) serotonin
(d) tyrosine
(e) tryptophan
(c) serotonin
Which of the following neurotransmitters is inhibited by strychnine?
(a) serotonin
(b) epinephrine
(c) norepinephrine
(d) glycine
(e) aspartate
(d) glycine
Which of the following is not a neuromodulator?
(a) Dopamine
(b) Serotonin
(c) Acetylcholine
(d) Histamine
(e) None of the above
(e) None of the above
Which of the following is not an excitatory neurotransmitter?
(a) epinephrine
(b) serotonin
(c) histamine
(d) glutamate
(e) acetylcholine
(b) serotonin
Tetrahydrobiopterin (GH4) is a reductant in the metabolism of the following except;
(a) Catecholamine synthesis
(b) Nitric oxide (NO) synthesis
(c) Serotonin synthesis
(d) Phenylalanine catabolism
(e) Melanin synthesis
(e) Melanin synthesis
Which of the following is not true about epinephrine?
(a) It causes contraction of respiratory passages
(b) It increases the heart rate
(c) It promotes glycogenolysis
(d) It increases the blood pressure
(e) It acts primarily on muscle, liver and the adipose tissue
(a) It causes contraction of respiratory passages
Conversion of norepinephrine to epinephrine is a ________ reaction.
(a) redox
(b) methylation
(c) demethylation
(d) hydroxylation
(e) hydrolytic
(b) methylation
Acetylcholinesterase, an enzyme that hydrolyses acetylcholine has an essential ________ group at its active site.
(a) methyl
(b) sulfhydryl
(c) hydroxyl
(d) carboxyl
(e) amino
(c) hydroxyl
The diffusible agent produced by binding of acetylcholine to endothelial cells is ________.
(a) superoxide ion
(b) hydroxyl ion
(c) nitrous oxide
(d) nitric oxide
(e) hydrogen sulfide
(d) nitric oxide
Synthesis of epinephrine involves the participation of the following except ________.
(a) a transferase
(b) a decarboxylase
(c) a hydrolase
(d) a hydroxylase
(e) tetrahydrobiopterin
(c) a hydrolase
What is the name of the indolamine derived from tryptophan?
(a) GABA
(b) alanine
(c) serotonin
(d) glutamate
(e) aspartate
(c) serotonin
Total amnesia may occur when ________.
(a) there is no sleep
(b) serotonin stores are depleted by reserpine
(c) the brain relaxes
(d) total loss of acetylcholine
(e) nicotinic receptors are blocked by curare
(d) total loss of acetylcholine
Further notes:
Amnesia is abroad term that refers to memory loss. It can be temporary or permanent, and it can affect different types of memory.
Acetylcholinesterase catalyses a ________.
(a) synthetic reaction
(b) a redox reaction
(c) a cleavage reaction involving water
(d) a cleavage reaction involving inorganic phosphate
(e) none of the above
(c) a cleavage reaction involving water
Acetylcholinesterase has an essential ________ residue in its active site.
(a) sulfhydryl
(b) serine
(c) carboxyl
(d) threonine
(e) methyl
(b) serine
Which one of the following is a diffusible agent produced by binding of acetylcholine to endothelial cells?
(a) nitrous oxide
(b) hydrogen sulfide
(c) superoxide ion
(d) hydroxyl ion
(e) nitric oxide
(a) nitrous oxide
Regarding glutamine involvement in nucleotide biosynthesis:
(a) donates one carbon atom from its alpha-carboxylic acid group
(b) donates 1 carbon and 1 nitrogen
(c) donates one N atom from its alpha-amino group
(d) donates one N atom from its amide group
(e) none of the choices is true
(d) donates one N atom from its amide group
