Question

Epinephrine opposes insulin action. It works through the B2 adrenergic receptor to elicit the CAMP signaling cascade (Tymoczko3e Fig 13.4; Berg8e Fig. 14.1). The image below is of the hormone- bound, activated form of the B2 adrenergic receptor. The red and blue lines demarcate the boundaries of the outer and inner leaflets of the lipid bilayer, respectively. Recall that one complete turn of an a- helix contains 3.4 residues and is 5.4 Angstroms in length. Using the alpha helix as a ruler and the figure below, choose the best answer that describes the thickness of the lipid bilayer. 5 turns, 17 residues, 27 Angstroms 6 turns, 20 residues, 32 Angstroms 7 turns, 24 residues, 38 Angstroms 8 turns, 27 residues, 43 Angstroms

Epinephrine opposes insulin action. It works through the β₂ adrenergic receptor to elicit the cAMP signaling cascade (Tymoczko3e Fig 13.4; Berg8e Fig. 14.1). The image below is of the hormone-bound, activated form of the  β₂ adrenergic receptor. The red and blue lines demarcate the boundaries of the outer and inner leaflets of the lipid bilayer, respectively. Recall that one complete turn of an α-helix contains 3.4 residues and is 5.4 Angstroms in length. Using the alpha helix as a ruler and the figure below, choose the best answer that describes the thickness of the lipid bilayer.

It is not 7 or 8 turns, I am wondering how to do this?

Answer 1

The given figure contains two β2 adrenergic receptors (B2ARs) which is a type of G Protein coupled Receptor (GPCR). whereas one receptor contains 7 transmembrane α-helices present in it.

Since one helix contain 3.4 residue, then 7 X 3.4 = 23.8 residues in it and it is 37.8 Angstroms in total length.

So, option 3 is correct one.