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Ch 5 - Cell Signaling in Physiology
Terms in this set (18)
The "signal" is the receptor activation, and "transduction" denotes the process by which a stimulus is transformed into a response
Receptor (receptor protein)
A specific protein in either the plasma membrane or the interior of a target cell that a chemical messenger binds with, thereby invoking a biologically relevant response in that cell.
The ability of a receptor to bind only one type or a limited number of structurally related types of chemical messengers. Only cellsthat express the correct receptor can bind a particular messenger.
The degree to which receptors are occupied by messengers. If all are occupied, the receptors are fully saturated; if half are occupied, the saturation is 50%, and so on.
The strength with which a chemical messenger binds to its receptor.
The ability of different molecules to compete with a ligand for binding to its receptor. Competitors generally are similar in structure to the natural ligand.
A molecule that competes with a ligand for binding to its receptor but does not activate signaling normally associated with the natural ligand. Therefore, an antagonist prevents the actions of the natural ligand. Certain types of antihistamines are examples of antagonists.
A chemical messenger that binds to a receptor and triggers the cell's response; often refers to a drug that mimics a normal messenger's action. Some decongestants are examples of agonists.
A decrease in the total number of target-cell receptors for a given messenger; may occur in response to chronic high extracellular concentration of the messenger.
An increase in the total number of target-cell receptors for a given messenger; may occur in response to a chronic low extracellular concentration of the messenger.
The increased responsiveness of a target cell to a given messenger; may result from up-regulation of receptors.
First, the extracellular chemical messengers (such as hormones or neurotransmitters) that reach the cell and bind to their specific plasma membrane receptors
substances that enter or are generated in the cytoplasm as a result of receptor activation by the first messenger.
the name for an enzyme that phosphorylates other proteins by transferring a phosphate group to them from ATP
G-protein- coupled receptors
a G protein serves as a switch to couple a receptor to an ion channel or to an enzyme in the plasma mem- brane
Summary of Common Mechanisms by Which Receptor Activation Influences Ion Channels
1. The ion channel is part of the receptor.
2. A G protein directly gates the ion channel.
3. A G protein gates the ion channel indirectly via production of a second messenger such as cAMP.
Common Mechanisms by Which Stimulation of a Cell Leads to an Increase in Cytosolic Ca2+ Concentration
I. Receptor activation
- Plasma-membrane Ca channels open in response to a first messenger; the receptor itself may contain the channel, or the receptor may activate a G protein that opens the channel via a second messenger.
- Ca2+ is released from the endoplasmic reticulum; this is
typically mediated by IP3.
- Active Ca2+ transport out of the cell is inhibited by a second
II. Opening of voltage-gated Ca2+ channels
Major Mechanisms by Which an Increase in Cytosolic Ca2+ Concentration Induces the Cell's Responses
- Ca2+ binds to calmodulin. On binding Ca2+, the calmodulin changes shape and becomes activated, which allows it to activate or inhibit a large variety of enzymes and other proteins. Many of these enzymes are protein kinases.
- Ca2+ combines with Ca2+-binding proteins other than calmodulin, altering their functions.
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