Flashcards in BIOL 0800 Reading- Chapter 5 Deck (100)
What is the first step in the action of any intercellular chemical messenger?
The binding of the messenger to specific target cell proteins known as receptors or receptor proteins
What is a receptor or receptor protein?
A specific target cell protein to which the messenger binds during intercellular chemical messaging
What is a chemical messenger?
What is signal transduction?
The sequence of events caused by the binding of a messenger to a receptor protein that leads to the cell's response to that messenger
What are the receptors that intercellular chemical messengers bind to?
Proteins or glycoproteins in the plasma membrane or cytosol or nucleus (usually the plasma membrane)
Why are the majority of receptors located in the plasma membrane?
Because the messengers are usually water soluble and can't diffuse across the lipid membrane
What is a receptor "superfamily?"
When receptor proteins for a group of messengers are structurally related, like for hormone receptors
If different types of cells have the same receptors for a particular messenger, does that messenger affect each of the cells the same way?
Nope: norepinephrine contracts certain blood vessel smoother muscle cells, but decreases insulin secretion of certain pancreatic endocrine cells
Why do some cells contain more than one difference receptor type for a single messenger?
Because the different types of receptors can have different effects on the cell even with the same messenger binding to them
What is affinity for a messenger?
The degree to which a particular messenger binds to its receptor
How does affinity affect binding?
High affinity means that the messenger will bind even at low concentrations, and low affinity requires high concentrations for binding
What is messenger saturation?
The degree to which receptors are occupied by messengers; if all are occupied, the receptors are fully saturated.
What is messenger competition?
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
Competition between what kind of messengers occurs most frequently, and what is this the basis for?
Closely related messengers, and underlies the action of many drugs
What are antagonists?
Drugs that block the endogenous messenger from binding but don't trigger the cell's response; example is beta blockers
What do beta blockers do?
Use epinephrine and norepinephrine to bind for receptors involved in high blood pressure and other diseases (beta-adrenergic) to prevent an increase in blood pressure that would have resulted from the epinephrine/norepinephrine
List two common antagonists.
Beta blockers and antihistamines
What are agonists?
Drugs that bind to a particular receptor type that do trigger the cell's response exactly as if the endogenous messenger had been bound
List one common example of use of agonists.
Phenylephrine or oxymetazoline decongestants that mimic the action of epinephrine to induce vasoconstriction in the nasal passages.
What is down regulation?
A decrease in the total number of target-cell receptors for a given messenger; mat occur in response to chronic high extracellular concentration of the messenger
What is a colloquial word for down regulation?
What is up regulation?
An increase in the total number of target cell receptors for a given messenger; mat occur in response to a chronic low extracellular concentration of the messenger
What is internalization and what does it affect?
When the entire receptor complex is taken in by endocytosis after the messenger binds, which increases degradation of the receptor and leads to down regulation
What is receptor activation?
The initial step leading to a cell's responses to the messenger, where the biding of the messenger to the receptor causes a change in the receptor's conformation
What are the five cellular responses that can constitute the changes in conformation of the receptor during receptor activation?
Permeability, transport properties, or electrical state of the plasma membrane; metabolism; secretory activity; rate of proliferation and differentiation; contractile or other activities
What is the "common denominator" to the variety of responses to receptor activation?
They're all directly due to alterations of particular cell proteins
What are signal transduction pathways?
The diverse sequences of events between receptor activation and cellular responses
What kinds of receptors are inside the cytosol rather than in the plasma membrane?
Receptors for lipid soluble messengers, because those can pass through the membrane
How do lipid soluble messengers generally act on cells?
Binding to intracellular receptor proteins