Final answer:
A protein may contain multiple TM helices because they are integral membrane proteins that must interact with the hydrophobic core of the lipid bilayer, allowing them to fulfill diverse functions like transport and signaling through their specific tertiary structures.
Step-by-step explanation:
A protein may have multiple transmembrane (TM) helices due to its role as an integral membrane protein. These integral membrane proteins require one or more alpha-helices to span the lipid bilayer and facilitate various functions like transport, signaling, or enzymatic activity. The tertiary structure of these proteins often features multiple alpha-helices or beta-sheets which allow for the stable interaction with the hydrophobic core of the membrane. These helices are right-handed and stabilized by intrachain hydrogen bonding, whereas beta sheets in the membrane can be arranged in parallel or antiparallel orientations.
Considering the diversity of membrane proteins' functions and the complexity of the cell membrane environment, having multiple TM helices enables the formation of pore-like structures or larger protein complexes. The specific arrangement of these helices and sheets allows proteins to adopt unique and specific conformations necessary for their biological function, possibly involving binding sites or channels for molecules to pass through the membrane.