EVERYDAY SCIENCE

Detailed explanation-1: -Endoplasmic reticulum is a network of membranes inside a cell through which proteins and other molecules move. Proteins are assembled at organelles called ribosomes.

Detailed explanation-2: -Proteins synthesized by the rough ER include the prominent milk protein casein, and whey proteins. These proteins are packaged into secretory vesicles or large micelles and travel through the Golgi network before fusing with the plasma membrane, releasing their contents into milk ducts.

Detailed explanation-3: -The RER is also located near the Golgi apparatus, which transports, modifies, and packages proteins for delivery to targeted destinations. Many proteins that are synthesized in the RER are packaged into vesicles and transported to the Golgi apparatus.

Detailed explanation-4: -The RER is associated with many roles in protein synthesis, which also include post-translational modifications, folding, and sorting. Membrane-bound ribosomes in the RER translate the mature mRNA transcript into amino acids that are attached to become polypeptides.

Detailed explanation-5: -COPII-coated vesicles transport cargo proteins from the ER to the Golgi; COPI-coated vesicles transport cargo in the retrograde direction (from the cis-Golgi back to the ER) and between Golgi cisternae; and clathrin-coated vesicles form from the plasma membrane and the TGN to fuse with endosomes or lysosomes (Fig. 1).