Question

The main organelle involved in modification and routing of newly synthesized proteins to their destinations is

• A. mitochondria
• B. endoplasmic reticulum
• C. lysosome
• D. chloroplast

Answer 1

Answer: (B)

Porter coined the name Endoplasmic Reticulum (ER). It is a network of tubules, vesicles and cisternae within an eukaryotic cell (absent in prokaryotic cells). Two types of ER are recognised on the basis of presence/absence of tibosomes on the wall of the ER.
(i) Smooth ER-Wall of this ER does not has ribosomes. Smooth ER helps in the synthesis of lipid and glycogen.
(ii) Rough ER-Wall of this ER contains ribosomes. Rough ER is involved in protein synthesis and transfer.
Protein synthesis takes place in ribosomes attached on wall of ER. Newly formed protein enters within the cavity of rough ER and follows following path:
Protein $\to$ Cavity of rough ER $\to$ Cavity of smooth ER $\to$ Golgi membrane $\to$ Lysosomes or transport vesicles or secretory granules.