why are hydrophobic amino acids located in the interior

Glycophorin A monomers pair to form dimers in the plasma membrane. One glycophorin A polypeptide with its hydrophobic trans-membrane alpha helix is cartooned below. As an example, consider the amino acids in the alpha-helical domain of the red blood cell protein glycophorin A, a membrane protein that prevents red blood cells from aggregating, or clumping in the circulation. The alpha helical domains that anchor proteins in membranes are mostly non-polar and hydrophobic themselves. N-terminal end of a plasma membrane polypeptide always ends up exposed to the outside of the cell.

Transmembrane proteins can in fact cross a membrane more than once, which also determines the location of its N- and C-termini. How a transmembrane protein inserts into the membrane during synthesis dictates the locations of its N- and C-terminus. The protein on the left crosses the membrane once, while the one on the right crosses the membrane three times. Two trans-membrane proteins are cartooned below. Hydrophilic domains tend to have more tertiary structure with hydrophilic surfaces, and so face the aqueous cytosol and cell exterior. Shown at the right is the structure of serine.The hydrophobic domain of integral membrane proteins consists of one or more alphahelical regions that interact with the hydrophobic interior of the membranes. These amino acids are usually found at the surface of proteins, as discussed in the Proteins 2 module. These are serine (Ser), threonine (Thr), cysteine (Cys), asparagine (Asn), glutamine (Gln), and tyrosine (Tyr). Six amino acids have side chains that are polarīut not charged. This fact has important implications for proteins' tertiary structure (see the Proteins 2 module for a discussion of tertiary structure). These side chains are composed mostly of carbon and hydrogen, have very small dipole moments, and tend to be repelled from water. Shown at the right is the structure of valine. Side chains are glycine (Gly), alanine (Ala), valine (Val), leucine (Leu), isoleucine (Ile), proline (Pro), phenylalanine (Phe), methionine (Met), and tryptophan (Trp). The nine amino acids that have hydrophobic

Amino acids are grouped according to what their side chains are like.

Why are hydrophobic amino acids located in the interior