BIOL 301 class 21 Flashcards
many different types of hormones exist
receptors can be membrane-bound or cytoplasmic
signal transduction
1) G protein-coupled receptor
2) receptor tyrosine kinase
3) receptor guanylyl cyclase
4) gated ion channel
5) adhesion receptor (integrin)
6) nuclear receptor
how is an extracellular signal like glucagon and epinephrine “transduced” into an intracellular response?
- the glucagon receptor is a g-protein coupled receptor (GPCR)
the GPCR superfamily
- make up 1-3% of a typical mammalian genome
- 7-Pass transmembrane protein; so-called serpentine receptors
- N terminus is located on the extracellular side of the membrane
- the C terminus is intracellular
- Upon ligand binding, GPCRs interact with heterotrimeric G proteins (consisting of α, β, and γ subunits) located inside the cell. This interaction leads to the activation of G proteins by promoting the exchange of GDP for GTP on the α subunit.
cell surface receptors like GPCRs transduce the binding of an external ligand into signals that can impact gene expression in the nucleus
glucagon or epinephrine binding to a cell surface hormone receptor leads to an increase in cellular cAMP
glucagon binding to its receptor in the membrane activates production of cAMP as a “second messenger” that leads to a kinase cascade and biological responses
what are “second messengers”
bioactive molecules that are generated by receptor activation
(Hetero) Trimeric G-Proteins (the “GP” in GPCR)
hormonal activation of glycogen phosphorylase was shown to be dependent upon GTP
- this led to the discovery of trimeric G-proteins associated with the receptor
epinephrine signaling acts through a GPCR