The transmembrane segment of a single-pass integral membrane protein is typically:

1. The segment has to be long enough to span the hydrophobic core of the bilayer. 2. Too short and it would not reach; much longer and it would not fit. 3. Single-pass integral membrane proteins usually have a hydrophobic transmembrane segment that consists of 20 to 25 amino acids. 4. Complex proteins can be composed of up to 12 such segments. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_