The alpha-helix shown below is part of a water-soluble, globular protein. Note t

Question

The alpha-helix shown below is part of a water-soluble, globular protein. Note that some amino acids point "toward" you (Lys, Glu, Ser, Asp, etc.) and some point "away" from you (Phe, Ile, Val, Ile, etc.). Which side of the helix (the side with the amino acids pointing "toward" you or the side with the amino acids pointing "away" from you) would likely be the side of the helix that is in contact with the cytoplasm (the watery fluid inside all cells), as opposed facing inward toward the "core" of the protein?

Explanation / Answer

Lys, Ser, Glu and Asp are hydrophilic amino acids whereas Phe, Ile, Val, Ile are hydrophobic amino acids.

Hydrophilic amino acids seek contact with water whereas hydrophobic amino acids do not.

The hydrophilic amino acids tend to be on the outside of the protein molecules. Therefore the hydrophilic amino acids would be in contact with the cytoplasm. The hydrophobic amino acids would tend to orient towards the interior of the folded protein molecule.

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