In eukaryotic cells, what is the key difference between rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) in terms of structure and primary function?

• A. RER is found only in plant cells and SER is found only in animal cells.
• B. RER is the site of DNA replication, whereas SER is the site of transcription and mRNA processing.
• C. RER lacks ribosomes and is primarily involved in lipid synthesis, whereas SER is studded with ribosomes and is primarily involved in protein synthesis.
• D. RER is studded with ribosomes and is primarily involved in synthesis and initial processing of secreted and membrane proteins, whereas SER lacks ribosomes and is primarily involved in lipid synthesis and detoxification.

Answer: (D)