To answer the question of which of these cellular components is not involved in protein synthesis, we need to understand the roles of each option:
- Smooth Endoplasmic Reticulum (Smooth ER): The Smooth ER is primarily involved in lipid synthesis and detoxification processes. It does not play a direct role in protein synthesis.
- Rough Endoplasmic Reticulum (Rough ER): The Rough ER is studded with ribosomes and is directly involved in the synthesis of proteins, particularly those that are to be exported or inserted into membranes.
- The Golgi Complex: While the Golgi complex does not synthesize proteins, it modifies, sorts, and packages proteins that were made in the Rough ER for transport to their destinations.
- The Nucleus: The nucleus contains the genetic material and is responsible for transcription, the first step of protein synthesis where the DNA is used to produce mRNA.
- Ribosomes: Ribosomes are the molecular machines that actually assemble amino acids into proteins based on the sequence of the mRNA, making them essential for protein synthesis.
Based on this analysis, the component that is not involved in protein synthesis is the Smooth Endoplasmic Reticulum (Smooth ER). Therefore, the answer is A) Smooth ER.