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Receptors: Types and Functions
Receptors are like antennas of cells. They are the first people in the cell to receive an external signal sent by other cells in form of a chemical messenger.
Upon receiving the signal they transduce it into a response.
Domains on Receptor Molecule
Ligand Binding Domain
Recognizes a specific ligand molecule.
Effector Domain
Produce downstream effect.
Location of Receptors
On Cell Membrane
For hydrophilic messengers.
Hydrophilic messengers cannot cross the cell membrane
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Receptors for them are expressed on the cell membrane
Inside the Cell
For hydrophobic messengers.
Hydrophobic messengers can cross the cell membrane
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Receptors for them are inside the cell
Types of Receptors
Ligand Gated Ion Channels
Located on the cell surface.
Here the same protein molecule works as a channel as well as a receptor.
The Channel portion allows the passage of small ions ⟶ receptors are also called ionotropic receptors.
Receptor portion binds various ligands and controls the opening and closing of the channel.
They are involved in signaling between electrically excitable cells i.e. neurons and muscle cells
E.g. acetylcholine receptors on the muscle end plate are sodium channels.
G Protein-Coupled Receptors
They are the largest family of cell surface receptors.
On the cytoplasmic side, they are associated with G proteins.
Regulate functions of various enzymes and ion channels of the cell.
E.g. Adrenergic receptors on cardiac muscle cells.
Catalytic Receptors
Located on the cell surface.
Have an enzymatic activity of their own or are associated with another enzymatic molecule.
Mostly the enzymatic activity is kinase or phosphatase.
E.g. Insulin receptors (have their own enzymatic activity) and erythropoietin receptors (associated with another enzymatic molecule)
Nuclear Receptors
Located inside the cell.
Regulate gene expression.
As protein synthesis takes time, their effect takes longer to appear.
Exact location inside the cell:
Cytoplasm: e.g. glucocorticoid and mineralocorticoid receptors.
Nucleus: e.g. estrogen and progesterone receptors.
Bound to DNA: e.g. thyroid hormone and retinoic acid receptors.
Receptors that Undergo Cleavage
Not typical receptors, but work like receptors.
Ligand binding
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Regulated Intramembrane Proteolysis (RIP) of the receptor molecule
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Cytoplasmic fragments
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Go to the nucleus
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Regulate gene expression
E.g. Sterol regulatory element-binding protein found on endoplasmic reticulum
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Related Videos:
See acetylcholine receptors playing role in exciting muscle cell: ▶️ Neuromuscular Junction and Neuromuscular Transmission
See adrenergic receptors playing role in controlling heart rate: ▶️ Effect of Parasympathetic and Sympathetic Activation on SA Node: Autonomic Control of Heart Rate
See insulin receptors in action: ▶️ Mechanism of Action of Insulin
See thyroid hormone receptors in action: ▶️ Mechanism of Action of Thyroid Hormones
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