Receptors Flashcards
Define ligand.
Any molecule that binds specifically to a receptor site
AGONIST: activates a receptor
ANTAGONIST: binds to a receptor without activating
note: ligands have high affinity as ligand is diluted on its way to receptor
Define receptor.
Molecule that recognises specifically a second molecule (ligand) or family of molecules, and which in response to ligand binding brings about regulation of a cellular process
Give some examples of processes regulated by receptors.
- signalling by hormones/local chemical mediators
- neurotransmission
- cellular delivery
- control of gene expression
- cell adhesion
- modulation
Give some examples of membrane-bound receptors with intrinsic ion channels.
- nAChR (gated Na+, K+, & Ca2+ channel - DEPOLARISATION)
- GABA (gated Cl- channel - HYPERPOLARISATION/IPSP)
- glycine (gated Cl- channel - HYPERPOLARISATION/IPSP)
- glutamate (gated Ca2+ channel - DEPOLARISATION)
- IP3 (gated ca2+ release from ER - MUSCLE CONTRACTION)
Describe the structure of nAChR channels.
Pentamer: 2 alpha subunits (ACh binding site) + beta, gamma, delta subunits
Give examples of membrane bound receptors with integral enzyme activity, and explain how they work.
Growth factor receptors e.g. insulin, platelet-derived growth factor
Binding of agonist to binding domain (N) autophosphorylates tyrosine residues in catalytic domain (C)
Tyrosine activates adjacent enzyme (possibly through transducer e.g. insulin receptor substrate)
Give an example of a membrane-bound receptor which signals through transducing proteins.
GTP-binding regulatory proteins (G-proteins = 7 transmembrane domain)
Give an example of intracellular receptors.
Receptor which binds steroids
On binding exposes DNA binding region
DNA transcription can be modified/regulated
Define phagocytosis, pinocytosis, and endocytosis.
Phagocytosis = engulfing and ingestion of micro-organisms, other cells, or foreign bodies by phagocytes
Pinocytosis = invagination of the plasma membrane allowing uptake of extracellular solutes (fluid) into vesicles
Endocytosis = selective internalisation of molecules into the cell by binding to specific cel surface receptors
Outline receptor-mediated endocytosis of LDL
- LDL binds to clathrin in coated pits
- Coated vesicle endocytosed
- Vesicle uncoated (ATP needed) and clathrin recycled
- LDL enters endosome (compartment of uncoupling of receptor and ligand - CURL) - pH 6.0
- LDL de-esterified in lysosome and cholesterol is produced
LIGAND DEGRADED, RECEPTOR RECYCLED
Outline receptor-mediated endocytosis of iron.
- Ferrotransferrin (Fe3+) binds to clathrin in coated pit
- Coated pit endocytosed and uncoated (ATP required)
- Fe3+ released from transferrin in CURL (pH 5.0)
- Apotransferrin recycled back to cell membrane surface, where it dissociates from the receptor
LIGAND RECYCLED, RECEPTOR RECYCLED
Outline receptor-mediated endocytosis of insulin receptors.
LIGAND DEGRADED, RECEPTOR DEGRADED
Therefore no. of receptors present can be regulated (see insulin resistance)
Outline receptor-mediated endocytosis of immunoglobulin.
- IgA binds to receptor in coated pits
- Endocytosis of coated pit, which is then uncoated (ATP required?)
- IgA remains bound to receptor in endosome
- IgA cleaved from receptor in bile
LIGAND TRANSPORTED, RECEPTOR TRANSPORTED
Outline how viruses enter and multiply in cells using coated pits.
- Viruses bind to cells by associating with cell receptors
- Enter via clathrin-coated pits
- Unfold hydrophobic domains in response to acidic pH of endosome
- Insert membrane fusion proteins into the endosome membrane and release genomic RNA into cell cytoplasm
- Use host cell machinery to replicate RNA and capsid proteins to bud new viruses
What is the difference between homologous and heterologous desensitisation?
HOMOLOGOUS = continuous stimulation of a receptor by an agonist results in desensitisation of the receptor to that agonist alone (only signal from stimulated receptor is reduced)
HETEROLOGOUS = repeated stimulation of a receptor by an agonist results in desensitisation of the receptor to that agonist AND other agonists in the same class (receptors for several agonists become less effective even when only one agonist has been continuously applied)
