Clear view: schematic shapes. Small molecules enlarged; spacing and timing are illustrative.
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First messenger
Adrenaline absentSecond messenger
cAMP · lowCell response
Glycogen storedThe molecular view imports atomic coordinates from the Protein Data Bank. The clear view is deliberately schematic. Both use the same teaching sequence; neither calculates molecular dynamics or predicts binding rates.
Protein files load over the internet. After loading them, Save offline copy bundles their coordinates into a new HTML file. No installation, account, or server is needed to open that copy.
Structural snapshots, not a filmed reaction. Proteins are shown as a Cα backbone trace with optional heavy-atom detail. Waters, crystallisation helpers and unrelated ligands are omitted. Missing residues are not invented. Chains may be separated or reoriented for teaching; animated encounters are not atomic docking predictions.
Representative proteins. The β₂ receptor and liver glycogen phosphorylase are human. Other entries contain mammalian homologues or engineered constructs. Adenylyl cyclase 9 is used to show a real membrane cyclase, not to assert that this is the specific dominant cyclase isoform in a hepatocyte. Its deposited conformation is not proof that it is actively catalysing at every displayed stage.
The route is selective. This lab isolates β₂/Gs/cAMP signalling. Adrenaline can also signal through other receptor subtypes. Calcium/calmodulin regulation of phosphorylase kinase, debranching enzymes, inhibition of glycogen synthesis, receptor desensitisation and other pathways are omitted. The kinase icon represents a whole functional enzyme, but its PDB model shows only a catalytic-domain fragment.
Product identity matters. Glycogen phosphorylase releases glucose 1-phosphate from non-reducing ends using inorganic phosphate. Additional liver reactions convert this to glucose 6-phosphate, then free glucose; the final dephosphorylation involves the endoplasmic reticulum. This conversion and export are explained, not animated as if they occur in one step.
Small molecules. Embedded cAMP, ATP, GTP, GDP and AMP conformers were computed with RDKit from RCSB Chemical Component Dictionary identities. They are not crystallographic coordinates. Adrenaline uses the embedded experimental ALE A1402 heavy-atom coordinates extracted from 4LDO, not a computed conformer. The coordinate excerpt is explicitly labelled as a ligand-only extract. Hydrogen atoms, ionisation state changes, waters and counterions are not displayed.
The core explanation follows the supplied textbook topic: a hormone binds to a specific target-cell receptor, a G-protein activates adenylyl cyclase, and ATP is converted into cAMP to trigger intracellular reactions. GDP is exchanged for GTP; the active G-protein has GTP bound to it. PKA, the individual cascade enzymes and glycogen products provide optional molecular detail.
Molecular Biology of the Cell: G-protein-linked receptors and cyclic AMP
Reactome: glycogen breakdown · Reactome: cAMP reactions and PKA activation · RCSB CCD: cAMP · ATP · GTP · GDP