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Violet Floor

Methionine

Adrenaline

adrenergic receptors (GPCRs):

They are cell surface receptors that detect signals outside the cell and activate intracellular responses

features:

7 transmembrane α-helices (spans the membrane 7 times)

Extracellular side

Intracellular side

A neurotransmitter or hormone binds to the GPCR on the cell surface

G-protein activation

GPCR is coupled to a heterotrimeric G-protein (α, β, γ subunits)

Ligand binding changes GPCR shape → GDP on Gα is replaced by GTP → Gα activated

Activated Gα separates from βγ subunits → both can signal downstream targets

Second messenger generation

Common pathways:

Gs (stimulatory): activates adenylyl cyclase → ↑cAMP → activates PKA

Gi (inhibitory): inhibits adenylyl cyclase → ↓cAMP

Gq: activates phospholipase C → PIP2 → IP3 + DAG → ↑Ca²⁺ and PKC activation

Signal termination

Gα hydrolyzes GTP → GDP → reassociates with βγ → turns off signal

Receptor type:

α1 - Postsynaptic - Activates PLC → IP₃/DAG → ↑Ca²⁺ → excitatory

α2 - Presynaptic - Inhibits further neurotransmitter release → negative feedback

β1, β2, β3 - Postsynaptic / some presynaptic - ↑cAMP → PKA → modulates ion channels, excitability

G-protein coupled

Phenylalanine

Dopamine

acts on dopaminergic receptors (GPCRs):

Receptor type:

D1-like (D1, D5) - Postsynaptic - Activate Gs → ↑cAMP → PKA → excitatory/modulatory

D2-like (D2, D3, D4) - Pre- and postsynaptic - Activate Gi → ↓cAMP → inhibitory or autoreceptor feedback

Valine

GABA

stored in synaptic vesicles by VGAT (vesicular GABA transporter)

GABA-A - Postsynaptic - Ligand-gated Cl⁻ channel - Fast inhibitory hyperpolarization (Cl⁻ influx)

GABA-B - Pre- and postsynaptic - GPCR, Gi/o - Slow inhibitory signaling: ↓cAMP, ↑K⁺ efflux, ↓Ca²⁺ influx

GABA transporters (GATs) remove GABA from the synaptic cleft

Metabolized by GABA transaminase (GABA-T) → succinic semialdehyde → enters TCA cycle

Indigo

Leucine (UUR)

Glutamate

Glutamate binds postsynaptic receptors

Na⁺ and/or Ca²⁺ enter the postsynaptic neuron

Membrane depolarizes (EPSP)

Signal ends via glutamate reuptake

Glutamate receptor types:

Ionotropic (fast)

AMPA receptors

Na⁺ influx

Primary moment-to-moment signaling

NMDA receptors

Require glutamate + depolarization

Mg²⁺ block removed by activity

Ca²⁺ entry → synaptic plasticity & memory

Kainate receptors

Metabotropic (slow)

mGluRs

Astrocytes and safety control

Astrocytes remove glutamate using EAAT transporters

Convert glutamate → glutamine

Return glutamine to neurons for reuse

prevents excitotoxicity (cell damage from excess excitation)

Leucine (CUN)

Glycine

Isoleucine

Taurine

Blue

Tryptophan

Serotonin (5-HT)

Alanine

Histamine

Asparagine

Aspartate

Green

Cysteine

Glutathione

Tyrosine

Norepinephrine

Serine (UCN)

Acetylcholine

Yellow

Serine (AGY)

D-Serine

Glutamate

Adenosine

Glutamine

ATP

Orange

Proline

Anandamide (AEA)

Histidine

Endorphins (β-endorphin)

Arginine

Nitric Oxide

Red

Threonine

Neuropeptide Y (NPY)

Glycine

Somatostatin

Lysine

Cholecystokinin (CCK)

Aspartate

Enkephalins