Why are g-protein coupled receptors often known as 7tm receptors? a. they have 7 transmembrane β-pleated sheets. b. they have 7 transmembrane α-helices. c. they have 7 tyrosine-methionine dipeptides in their structure. d. they have 7 methionine-tryptophan dipeptides in their structure.

B

Explanation:

G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptor, and G protein–linked receptors (GPLR),comprises of a large protein family of receptors that discover molecules outside the cell and initiate internal signal transduction pathways and, eventually, cellular responses. They are called seven-transmembrane receptors because they pass through the cell membrane seven times

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this