What is the function of the organelle or structure indicated by the arrow?

What is the function of the organelle or structure indicated by the arrow?

• A. Packaging and modification of protein
• B. Protein synthesis
• C. Steroid synthesis
• D. Lipid synthesis

Answer: (B)

Protein synthesis is carried out by ribosomes. The arrow points to a ribosome, the cellular site where mRNA is read and amino acids are joined together to form a polypeptide chain. During translation, tRNAs bring specific amino acids that pair with codons on the mRNA, and peptide bonds link them in the correct order. If these ribosomes are on the rough endoplasmic reticulum, the nascent proteins often enter the ER lumen for folding and initial processing before they’re transported by the Golgi apparatus for packaging and shipment. The other options correspond to other organelles: packaging and modification of proteins is mainly a function of the Golgi, while steroid and lipid synthesis occur in the smooth endoplasmic reticulum.

Protein synthesis is carried out by ribosomes. The arrow points to a ribosome, the cellular site where mRNA is read and amino acids are joined together to form a polypeptide chain. During translation, tRNAs bring specific amino acids that pair with codons on the mRNA, and peptide bonds link them in the correct order. If these ribosomes are on the rough endoplasmic reticulum, the nascent proteins often enter the ER lumen for folding and initial processing before they’re transported by the Golgi apparatus for packaging and shipment. The other options correspond to other organelles: packaging and modification of proteins is mainly a function of the Golgi, while steroid and lipid synthesis occur in the smooth endoplasmic reticulum.