Cell signalling and glucose control, at a glance

A target cell needs a suitable receptor and downstream machinery; binding starts a pathway that changes cell behaviour.

• Reception: ligand binds receptor.
• Transduction: intracellular relays.
• Response: altered activity or gene expression.

Keep in mind: A membrane receptor can initiate a relay that activates nuclear transcription factors without the hormone entering the cell.

Catalytic relays amplify a signal; phosphatases and messenger breakdown help terminate it.

• cAMP is an intracellular second messenger.
• Kinases add phosphate; phosphatases remove it.
• Catalytic cascades can amplify and must be regulated.

Keep in mind: Phosphorylation can activate or inhibit depending on context, and phosphatases can reverse it.

Insulin binding activates its membrane receptor pathway, promoting glucose uptake and storage through tissue-specific responses.

• Beta cells release insulin when glucose rises.
• Insulin receptor: receptor tyrosine kinase.
• Uptake/storage responses lower blood glucose.

Keep in mind: It signals target cells to alter uptake and metabolism; cellular enzymes perform the reactions.

Glucagon acts through a G-protein-linked receptor, promoting hepatic glucose release; its effect opposes insulin in glucose homeostasis.

• Alpha cells release glucagon when glucose falls.
• Glucagon receptor: G-protein-linked.
• Liver glucose release raises blood glucose.

Keep in mind: It means the response opposes the deviation; after a fall, the corrective response raises the variable.