Examples of nuclear receptor in the following topics:
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- Nuclear receptors function as transcription factors because they can bind to DNA and regulate gene expression.
- Receptors that can directly influence gene expression are termed nuclear receptors.
- Type I nuclear receptors are located in the cytosol.
- In the absence of ligand, type II nuclear receptors often form a complex with co-repressor proteins.
- Hormone binding to the nuclear receptor results in dissociation of the co-repressor and the recruitment of co-activator proteins.
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- Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins).
- Recognition of the hormone by an associated cell membrane or an intracellular receptor protein.
- Nuclear hormone receptors are activated by a lipid-soluble hormone such as estrogen, binding to them inside the cell.
- Water-soluble hormones, such as epinephrine, bind to a cell-surface localized receptor, initiating a signaling cascade using intracellular second messengers.
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- A hormone receptor is a molecule that binds to a specific hormone.
- Receptors for peptide hormones tend to be found on the plasma membrane of cells, whereas receptors for lipid-soluble hormones are usually found within the cytoplasm.
- The number of these complexes is in turn regulated by the number of hormone or receptor molecules available, and the binding affinity between hormone and receptor.
- Lipophilic hormones—such as steroid or thyroid hormones—are able to pass through the cell and nuclear membrane; therefore receptors for these hormones do not need to be, although they sometimes are, located in the cell membrane.
- The thyroid hormone receptor (TR) heterodimerized to the RXR.
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- Muscle tone is controlled by neuronal impulses and
influenced by receptors found in the muscle and tendons.
- Connecting to the endomysium of a muscle fiber, muscle spindles are composed of
nuclear bag fibers and nuclear chain fibers.
- However, unlike skeletal muscle fibers where the nuclei are spread
out and located at the periphery of the cell, in nuclear bag and nuclear chain
fibers the nuclei are located in a central region which is enlarged in nuclear
bag fibers.
- Distinct stretch receptors called golgi tendon
organs assess the level of stretch within the tendon.
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- Sensory receptors can be classified by the type of stimulus that generates a response in the receptor.
- Sensory receptors perform countless functions in our bodies.
- Cutaneous receptors are
sensory receptors found in the dermis or epidermis.
- Encapsulated receptors consist of the remaining types of cutaneous
receptors.
- A tonic receptor is a sensory receptor that
adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that
adapts rapidly to a stimulus.
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- Although both ionotropic and metabotropic receptors are activated by neurotransmitters, ionotropic receptors are channel-linked while metabotropic receptors initiate a cascade of molecules via G-proteins.
- Two types of membrane-bound receptors are activated with the binding of neurotransmitters: ligand-gated ion channels (LGICs) inotropic receptors and metabotropic G- protein coupled receptors.
- Examples of metabotropic receptors include glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, most serotonin receptors, and receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides, and endocannabinoids.
- Since opening channels by metabotropic receptors involves activating a number of molecules in the intracellular mechanism, these receptors take longer to open than the inotropic receptors.
- While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread throughout the cell.
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- A receptor antagonist does not provoke a biological response upon receptor binding, but limits or dampens agonist-mediated responses.
- A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses.
- Binding to the active site on the receptor regulates receptor activation directly.
- The current accepted definition of receptor antagonist is based on the receptor occupancy model.
- Irreversible antagonists covalently bind to the receptor target and, in general, cannot be removed; inactivating the receptor for the duration of the antagonist effects is determined by the rate of receptor turnover, the rate of synthesis of new receptors.
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- Some sensory receptors can be classified by the physical location of the receptor.
- Sensory receptors code four aspects of a stimulus:
- Receptors are sensitive to discrete stimuli and are often classified by both the systemic function and the location of the receptor.
- Sensory receptors are found throughout our bodies, and sensory receptors that share a common location often share a common function.
- For example, sensory receptors in the retina are almost entirely photoreceptors.
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- Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
- This androgen insensitivity occurs when the receptors on the target cells are unable to accept the hormone due to an impairment in receptor shape.
- Target cells are capable of responding to hormones because they display receptors to which the circulating hormone can bind.
- Finally, hormone–receptor affinity can be altered by the expression of associated inhibitory or co-activating factors.
- In some instances, alterations of receptor structure due to a genetic mutation can lead to a reduction in hormone–receptor affinity, as in the case of androgen insensitivity.
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- Adrenergic receptors are molecules that bind catecholamines.
- There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 (a Gq coupled receptor) and α2 (a Gi coupled receptor).
- β-receptors have the subtypes β1, β2, and β3.
- Adrenaline or noradrenaline are receptor ligands to α1, α2, or β-adrenergic receptors (the pathway is shown in the following diagram).
- α1-adrenergic receptors are members of the G protein-coupled receptor superfamily.