A transmembrane protein has at least one polypeptide chain crossing the complete lipid bilayer. One crossing is single-pass; several crossings in one chain are multipass. Hydrophobic regions face the membrane interior, while hydrophilic regions can face water.[ref]
Cell Membranes. The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper; Cell Membranes, Membrane Proteins: spanning regions, single and multiple crossings
A tail-anchored protein has a membrane-spanning segment near its C-terminus; many reach the endoplasmic reticulum after biological translation.
