Endoplasmic Reticulum (ER) - Practice Questions & MCQ

Components of the Endomembrane System: Endoplasmic Reticulum (ER)

• Endoplasmic reticulum was discovered by Porter and Thomson in 1945. 
• It is a series of interconnected membranous sacs and tubules. 
• It can be connected with the nuclear membrane as well as the cell membrane. 
• Endoplasmic reticulum divides the intercellular space into two compartments as luminal (inside the ER) and extra-luminal (rest of the cytoplasm)

Endoplasmic Reticulum is of two types - rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).

(1) Rough Endoplasmic Reticulum (RER)

• It is called so due to the presence of ribosomes on the membrane that gives a studded appearance. 
• The newly synthesized polypeptide from the ribosome moves into the RER where it is modified. The modified polypeptide will then be transported transport via vesicles that bud from the RER’s membrane to the Golgi or the destination. 
• RER is abundant in cells that secrete proteins.

(2) Smooth Endoplasmic Reticulum (SER)

• There are no ribosomes attached to the membranes of SER. 
• Thus, SER is concerned with the synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storage of calcium ions. 
• In muscle cells, a specialized SER called the sarcoplasmic reticulum is responsible for the storage of the calcium ions that are needed to trigger the coordinated contractions of the muscle cells.

Endoplasmic reticulum can exist in three forms:

(a) Cisternae: Flat, interconnected sac-like parts of the ER.
(b) Vesicles: Oval or rounded bodies involved in the transport of molecules.
(c) Tubules: Tubular extensions connected with cisternae or vesicles.