Final answer:
The translocon orients proteins in the membrane based on the hydrophobicity of the signal anchor sequence, which traps the protein within the membrane. Multiple stop-transfer sequences allow for proteins to span the membrane multiple times, with the N-terminus typically exposed outside the cell.
Step-by-step explanation:
The orientation of proteins in the membrane by the translocon is determined primarily by the hydrophobicity of the signal anchor sequence. The signal anchor is a hydrophobic domain within the polypeptide chain that acts as a stop-transfer sequence, trapping the protein within the lipid bilayer. Integral membrane proteins may contain multiple stop-transfer sequences, allowing them to span the membrane multiple times. These hydrophobic alpha helical domains are non-polar and ensure the proper insertion into the membrane. Additionally, N-terminal signal sequences guide ribosomes to the rough endoplasmic reticulum (RER), where synthesis begins, and once the protein reaches its destination, these signal sequences are typically removed.
The correct answer to the question is, therefore, C) Hydrophobicity of signal anchor. This property ensures that the integral membrane proteins are oriented correctly, with the N-terminus of a plasma membrane polypeptide usually exposed to the outside of the cell. The process involves various steps including the synthesis starting with the translation initiation complex, elongation, and movement of ribosomes along mRNA—termed as translocation, which is facilitated by elongation factor-G (EF-G), also known as translocase.