Final answer:
Transmembrane segments are hydrophobic regions found in transmembrane proteins that span the cell membrane. Common amino acids in transmembrane segments include alanine, glycine, valine, leucine, isoleucine, and phenylalanine.
Step-by-step explanation:
Transmembrane segments are found in transmembrane proteins, which are also known as integral membrane proteins. These proteins have hydrophobic regions that span the lipid bilayer of the cell membrane. The transmembrane segments typically consist of 20-25 amino acids and can either partially or fully cross the membrane. Some common amino acids found in transmembrane segments include alanine (A), glycine (G), valine (V), leucine (L), isoleucine (I), and phenylalanine (F).