🧪 General Principles🟢 BasicCell Signaling

Second Messenger Systems

The intracellular signals that relay a hormone's message from a surface receptor to the machinery inside the cell.

Key points

A hormone (the first messenger) binds a surface receptor and generates an intracellular second messenger, which greatly amplifies the signal.
In the cyclic AMP system a G-protein-coupled receptor activates adenylyl cyclase to make cyclic AMP, which activates protein kinase A.
In the phospholipase C system, PIP2 is split into IP3 and DAG; IP3 releases calcium from stores and DAG activates protein kinase C.
Calcium itself acts as a second messenger, frequently working through the binding protein calmodulin.
Some signals such as atrial natriuretic peptide and nitric oxide act through cyclic GMP.
Water-soluble hormones like peptides and catecholamines use surface receptors and second messengers, whereas steroid and thyroid hormones enter the cell and act on gene transcription directly.

Gs raises cyclic AMP; Gq raises IP3, DAG and calcium — the receptor's G-protein decides which second messenger fires.

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🧪 General Principles🟢 BasicCell Signaling

The intracellular signals that relay a hormone's message from a surface receptor to the machinery inside the cell.

A hormone (the first messenger) binds a surface receptor and generates an intracellular second messenger, which greatly amplifies the signal.
In the cyclic AMP system a G-protein-coupled receptor activates adenylyl cyclase to make cyclic AMP, which activates protein kinase A.
In the phospholipase C system, PIP2 is split into IP3 and DAG; IP3 releases calcium from stores and DAG activates protein kinase C.
Calcium itself acts as a second messenger, frequently working through the binding protein calmodulin.
Some signals such as atrial natriuretic peptide and nitric oxide act through cyclic GMP.
Water-soluble hormones like peptides and catecholamines use surface receptors and second messengers, whereas steroid and thyroid hormones enter the cell and act on gene transcription directly.

Gs raises cyclic AMP; Gq raises IP3, DAG and calcium — the receptor's G-protein decides which second messenger fires.