Question

During endogenous antigen processing, the antigens are cleaved in which of the following organelle?

• A. Endoplasmic reticulum
• B. Proteosomes
• C. Golgi bodies
• D. Lysosomes

Answer 1

Answer: (B)

Proteosomes

The endogenous pathway is used to present cellular peptide fragments broken down by proteosomes on the cell surface of MHC class I molecules. Transporter associated with antigen processing spans the membrane of the rough endoplasmic reticulum and transports the peptides into the lumen of the rough endoplasmic reticulum. Once the peptide is transported into the ER lumen it binds to the cleft of the MHC class I molecule, stabilizing it and allowing it to be transported to the cell surface by the Golgi apparatus. Thus the correct answer is option B.