BIOL 301 class 21

Question 1

many different types of hormones exist

Answer 1

receptors can be membrane-bound or cytoplasmic

Question 2

signal transduction

Answer 2

1) G protein-coupled receptor
2) receptor tyrosine kinase
3) receptor guanylyl cyclase
4) gated ion channel
5) adhesion receptor (integrin)
6) nuclear receptor

Question 3

how is an extracellular signal like glucagon and epinephrine “transduced” into an intracellular response?

Answer 3

• the glucagon receptor is a g-protein coupled receptor (GPCR)

Question 4

the GPCR superfamily

Answer 4

• 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.

Question 5

cell surface receptors like GPCRs transduce the binding of an external ligand into signals that can impact gene expression in the nucleus

Question 6

glucagon or epinephrine binding to a cell surface hormone receptor leads to an increase in cellular cAMP

Answer 6

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

Question 7

what are “second messengers”

Answer 7

bioactive molecules that are generated by receptor activation

Question 8

(Hetero) Trimeric G-Proteins (the “GP” in GPCR)

Answer 8

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

Question 9

epinephrine signaling acts through a GPCR