Final answer:
An integral membrane protein with a single helix typically spans the membrane with 20-25 hydrophobic amino acids. The distribution of amino acids in membranes is such that hydrophobic amino acids interact with the lipid bilayer, while hydrophilic amino acids are positioned to interact with the aqueous environment or are shielded within protein structures.
Step-by-step explanation:
An integral membrane protein with a single alpha-helix typically requires 20-25 amino acids to span the membrane. These amino acids must be predominantly hydrophobic to interact with the hydrophobic core of the lipid bilayer. Proteins embedded in a lipid bilayer will therefore have a significant proportion of nonpolar amino acids in their membrane-spanning domains, while any charged or polar amino acids present are usually positioned in a way that allows them to form interactions with other protein segments or shielded from the fatty environment. Hydrophobic amino acids predominantly comprise the alpha-helical domains that anchor these proteins in the membrane. This is exemplified by proteins like glycophorin A in red blood cells, which demonstrate that integral membrane proteins can have hydrophobic trans-membrane alpha helices crucial for their function and placement within the membrane. Regarding the surfaces of proteins, soluble proteins will typically have hydrophilic amino acids on their surface, allowing them to interact with the aqueous environment. In contrast, the interior often contains more hydrophobic amino acids. This distribution is inverted in membrane proteins, where the hydrophobic amino acids are on the surface in contact with the lipid bilayer, and any hydrophilic regions protrude to the aqueous cytosol and cell exterior.