Insulin receptors at Higher Level: An AHL statement: a receptor that is also an enzyme.
Practise this as you read
- Outline how insulin increases glucose uptake.
- Identify the ligand of a tyrosine kinase receptor.
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The big idea: The insulin receptor is a transmembrane receptor that is also an enzyme: its parts inside the cell are tyrosine kinases. When insulin binds, the receptor phosphorylates tyrosines on itself, using ATP. This starts a pathway that sends glucose transporters to the plasma membrane, so more glucose enters the cell.
The points to remember
- The insulin receptor is a pair of subunits across the membrane.
- Its inside parts are tyrosine kinases: enzymes that add phosphate to tyrosine.
- Insulin binds, and the receptor phosphorylates itself using ATP.
- The phosphorylated receptor activates relay proteins.
- Vesicles with glucose transporters fuse with the membrane: more glucose in.
Remember it as: Insulin binds, receptor phosphorylates itself, transporters arrive.
Real example: after a meal. After a meal, insulin from the pancreas reaches muscle and fat cells. Within minutes, more glucose transporters sit in their plasma membranes, and blood glucose falls.
Trap: A kinase adds phosphate; the receptor is the kinase here. There is no G protein in this pathway.
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How it is asked: Expect an MCQ asking which ligand uses a tyrosine kinase receptor, or an Outline question on how insulin increases glucose uptake.
IB-style questionOutline[4 marks]
Outline how insulin increases the uptake of glucose by a muscle cell.
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See the answer broken into clear points, with guidance on how each point earns marks.