Chapter 5 Cell Signalling in Physiology Flashcards
The first step in the action of any intercellular chemical messenger is the binding of the messenger to specific target-cell proteins known as _________
The first step in the action of any intercellular chemical messenger is the binding of the messenger to specific target-cell proteins known as receptors (or receptor proteins)
A chemical messenger is a _____ and the receptor has a _____ _____ for that specific messenger
A chemical messenger is a ligand and the receptor has a binding site for that specific messenger
The binding of a messenger to the receptor changes the ______ (_____ structure) of the receptor
The binding of a messenger to the receptor changes the conformation (tertiary structure) of the receptor
Changing the conformation of a receptor effectively _____ the receptor
Changing the conformation of a receptor effectively activates the receptor
What is signal transduction?
Signal transduction is the process by which the binding of a messenger to a receptor activates a sequence of events that lead to a cell response
signal= receptor activation
transduction= the process by which a stimulus is transformed into a response
Receptors that bind intercellular chemical messengers are ______ or _____ located either in the ______ or inside the cell in the _____ or the ______
Receptors that bind intercellular chemical messengers are proteins or glycoproteins located either in the plasma membrane or inside the cell in the nucleus or the cytosol
Why is the plasma membrane the most common location for receptors?
A large number of messengers are water-soluble (not lipid-soluble) and therefore cannot diffuse across the plasma membrane
Plasma membrane receptors are _____, that is, they span the entire membrane thickness
Plasma membrane receptors are transmembrane proteins, that is, they span the entire membrane thickness
Arriving chemical messengers bind to the extracellular parts of the receptor; the intracellular regions of the receptors are involved in ______ _____ events
Arriving chemical messengers bind to the extracellular parts of the receptor; the intracellular regions of the receptors are involved in signal transduction events
Intracellular receptors exist in either the _____ or the _____
Intracellular receptors exist in either the cytosol or the nucleus
Like plasma membrane receptors, intracellular receptors have a segment that binds the ______ and segments that act as _______ ______. Unlike plasma membrane receptors, intracellular receptors also have a segment that binds to______
Like plasma membrane receptors, intracellular receptors have a segment that binds the messenger and segments that act as regulatory sites. Unlike plasma membrane receptors, intracellular receptors also have a segment that binds to DNA
What is a key distinction between Plasma Membrane Receptors and Intracellular receptors?
Plasma membrane receptors can transduce signals without interacting with DNA whereas all intracellular receptors transduce signals through interactions with genes
What are the four major features that define the interactions between receptors and their ligands?
- specificity
- affinity
- saturation
- competition
What is Receptor specificity?
The ability of a receptor to bind to only one type (or a limited number of structurally related types) of chemical messengers.
- means that only cells that express the particular receptor will be affected by a particular messenger
What is saturation (concerning receptors)?
The degree to which receptors are occupied by messengers.
If all are occupied the receptors are fully saturated; if only half are occupied the receptors are at 50% saturation and so on
What is affinity (in regards to receptors)
The strength with which a chemical messenger binds to its receptor
higher affinity = higher chance of bonding
What is receptor competition?
The ability of different molecules to compete with a ligand for binding to its receptor
Competitors are usually similar in structure to the natural ligand
What is a receptor antagonist?
A molecule that competes with a ligand for binding but does not activate signalling normally associated with the natural ligand
i.e. Antagonists prevent the actions of the natural ligand
eg certain antihistamines
What is a receptor agonist?
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
eg some decongestants are agonists
What is down regulation (terms of receptors)? When might it occur?
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
What is up-regulation (in terms of receptors) and when might it occur?
An increase in the total number of target-cell receptors available for a given messenger; may occur in response to a chronic low extracellular concentration of the messenger
What is increased sensitivity (in regards to receptors)?
The increased responsiveness of a target cell to a given messenger; may result from up-regulation of receptors
The general term for a compound that blocks the action of a chemical messenger is:
Antagonist
The true chemical messenger is termed the ______ messenger
The true chemical messenger is termed the endogenous messenger
Down regulation represents what kind of feedback mechanism?
Negative Feedback:
intense prolonged stimulation results in fewer receptors = reduce cell’s responsiveness to frequent or intense stimulation (i.e desensitize the cell)
How is down regulation possible?
there is continuous synthesis and degradation of receptors
The main mechanism of down-regulation of plasma membrane receptors is:
Internalization
What happens during internalization?
- messenger binds to receptor
- stimulates messenger-receptor complex to be taken into the cell via receptor-mediated endocytosis
- increases rate of degradation within the cell
- higher concentration of messenger = more internalization = gradual decrease in receptors
up regulation is the _________ of a cell receptor to a messenger as a result of prolonged exposure to low messenger concentrations
up-regulation is the increased sensitivity of a cell receptor to a messenger as a result of prolonged exposure to low messenger concentrations
How is up-regulation and down-regulation an example of the principle of homeostasis?
Acts to return signal strength to normal when the concentration of messengers varies above or below normal
What is receptor activation?
the conformation change that occurs when a messenger binds to a receptor
What are five possible types of cell responses to a messenger?
Changes in the
- permeability, transport properties, or electrical state of the plasma membrane
- metabolism
- secretory activity
- rate of proliferation and differentiation
- contractile or other activities
The diverse sequences of events that link receptor-activation to cellular responses are termed:
Signal transduction pathways
Lipid soluble messengers include:
hydrophobic substances such as steroid hormones or thyroid hormones
Lipid soluble messengers bind to _____ receptors (intracellular receptors)
Lipid soluble messengers bind to nuclear receptors (intracellular receptors)
in a few cases, inactive intracellular receptors are in the ______ and move into the _____ after binding to their ligand
in some cases, inactive intracellular receptors are in the cytosol and move into the nucleus after binding to their ligand
Most of the inactive intracellular receptors are located in the _____ where they bind to and are activated by their respective ligands
Most of the inactive intracellular receptors are located in the nucleus where they bind to and are activated by their respective ligands
Intracellular receptor activation leads to altered rates of _____ of one or more genes in a particular cell
Intracellular receptor activation leads to altered rates of transcription of one or more genes in a particular cell
Is it possible for more than one gene to be subject to control by a single receptor site?
Example?
Yes
Adrenal gland hormone cortisol activates numerous genes involved in the coordinated control of cellular metabolism and energy balance
in some cases, the transcription of a gene (or genes) may be _____ by the activated receptor
Example?
in some cases, the transcription of a gene (or genes) may be decreased by the activated receptor
Cortisol inhibits transcription of several genes whose protein products mediate inflammatory responses (anti-inflammatory)
Water soluble messengers include most ______ hormones, ______ and _____ and _____ compounds
Water soluble messengers include most polypeptide hormones, neurotransmitters, and paracrine and autocrine compounds
What are first messengers?
extracellular chemical messengers that reach the cell and bind to their specific plasma membrane receptors
What are second messengers?
substances that enter (or are generated in) the cytoplasm as a result of receptor activation by the first messenger
-chemical relays from plasma membrane to biochemical machinery within the cell
What is protein kinase?
enzyme that phosphorylates other proteins by transferring a phosphate group to them from ATP
-alters protein’s activity by allosterically changing tertiary structure of a protein
