BIOC32H3 Lecture 6: The Chemical Synapse II
LECTURE 6
BIOC32
Neurotransmitters
● Can be classified based by chemical composition:
○ Amines
○ Amino acids
○ Acetylcholine
● Amines
○ Synthesized in body
○ Derived from amino acids
○ Derived from tyrosine (Catecholamines)
■ Dopamine
■ Adrenaline
■ Noradrenaline
○ Derived from tryptophan
■ Serotonin / 5HT
● Amino Acids
○ From glutamine
■ Glutamate
○ From glutamate
■ GABA
● Acetylcholine
○ Synthesized in body
○ Derived from acetate + choline
Biosynthesis, Release, and Catabolism of Catecholamines
1. Tyrosine transported into the axonal terminals
2. Converted to neurotransmitter by a series of enzymes
3. DOPA is the precursor for dopamine and noradrenaline
4. Dopamine is the precursor for noradrenaline
5. Enzyme content of presynaptic terminals determines whether dopamine, adrenaline or noradrenaline are
formed
6. Neurotransmitter in the synaptic cleft is taken back up by active transport
7. Excess neurotransmitter is broken down by enzymes in the cytoplasm of the presynaptic terminal
Biosynthesis and Recycling of Acetylcholine
1. Acetylcholine (Ach) made from choline and acetyl CoA
2. In synaptic cleft Ach is rapidly broken down by enzyme
acetylcholinesterase
3. Choline transported back into the axon terminal is used to make more
ACh
LECTURE 6
BIOC32
● You can find a lot of Ach at neuromuscular junction
Biosynthesis, release and Breakdown of other Neurotransmitters
● Taken up into presynaptic terminal by transporter (active reuptake) and broken down
● Taken up into presynaptic terminal by transporter (active reuptake) and broken
down or repackaged into synaptic vesicles
Neurotransmitter Binding to Receptor
● Finite number of receptors
● At low concentrations, there is a linear
relationship between NT concentration and amount
of NT bound to the receptor
● At high concentrations, receptors become
saturated
○ No more NT can bind
● Max number of NT bound to R = max downstream effect that the NT can cause
Neurotransmitters bind to diff subtypes of receptor (R)
● Receptor subtypes defined by the ligand (NT) that binds
● Adrenergic Rs
○ NT = noradrenaline or adrenaline
● G protein-coupled R (GPCR)
○ Alpha and beta subtypes
■ a1/a2
■ B1,B2,B3
● Dopaminergic Rs
○ NT = dopamine
○ GPCR
○ D1 and D2 sybtypes
Document Summary
Can be classified based by chemical composition: Neurotransmitter in the synaptic cleft is taken back up by active transport. 6: excess neurotransmitter is broken down by enzymes in the cytoplasm of the presynaptic terminal. Biosynthesis and recycling of acetylcholine: acetylcholine (ach) made from choline and acetyl coa. In synaptic cleft ach is rapidly broken down by enzyme acetylcholinesterase: choline transported back into the axon terminal is used to make more. You can find a lot of ach at neuromuscular junction. Taken up into presynaptic terminal by transporter (active reuptake) and broken down. Taken up into presynaptic terminal by transporter (active reuptake) and broken down or repackaged into synaptic vesicles. At low concentrations, there is a linear relationship between nt concentration and amount of nt bound to the receptor. Max number of nt bound to r = max downstream effect that the nt can cause. Neurotransmitters bind to diff subtypes of receptor (r)
