How long is the hydrophobic transmembrane segment of a typical single-pass integral membrane protein?

1. Integral proteins are integrated completely into the membrane structure. 2. Their hydrophobic membrane spanning regions interact with the hydrophobic region of the phospholipid bilayer. 3. A single-pass integral membrane protein usually has a hydrophobic transmembrane segment of 20 to 25 amino acids. 4. Two to six residues could not reach across a bilayer 5 to 10 nm thick, so that figure is far too short. 5. Sixty to eighty and 200 to 250 residues describe whole domains or whole small proteins rather than one spanning segment. 6. Some complex proteins are built from up to 12 such segments of a single protein folded into the membrane. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 5 "Structure and Function of Plasma Membranes", section 5.1 Components and Structure_