When a protein forms an alpha helix, the R groups of the amino acids are oriented outward and exposed on the outer surface of the helix. Which type of membrane associating protein is going to utilize an alpha helix that displays hydrophobic R groups on one side of the helix and hydrophilic R groups on the other side? (rather than having all of the exposed R groups as hydrophobic). Lipid-linked (protein contains a lipid anchor) Linked to an oligosaccharide chain Partial interaction of an alpha-helix Transmembrane protein with single alpha-helix
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In this case, the alpha helix displays hydrophobic R groups on one side and hydrophilic R groups on the other side. Show more…
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Protein A has a single transmembrane domain that is an alpha helix. Protein B has four transmembrane domains, each of which is an alpha helix, that together form a channel to transport a monosaccharide across the cell membrane. Consider the following amino acid sequence from part of a polypeptide (single letter code for amino acids): ...-A-F-N-Y-L-V-S-N-L-F-Q-T-A-A-S-Y-I-V-N-Q-... A. Could the sequence shown potentially form the alpha helix of protein A, one of the alpha helices of protein B, both helices, or neither helix? Explain your choice.
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Consider a transmembrane protein that forms a hydrophilic pore across the plasma membrane of a eukaryotic cell. When this protein is activated by binding a specific ligand on its extracellular side it allows $\mathrm{Na}^{+}$ to enter the cell. The protein is made of five similar transmembrane subunits, each containing a membrane-spanning $\alpha$ helix with hydrophilic amino acid side chains on one surface of the helix and hydrophobic amino acid side chains on the opposite surface. Considering the function of the protein as a channel for $\mathrm{Na}^{+}$ ions to enter the cell, propose a possible arrangement of the five membrane-spanning $\alpha$ helices in the membrane.
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