Endoplasmic Reticulum: Study Notes

For the complete syllabus, check out our PMDC MDCAT Syllabus 2025 article.

Endoplasmic Reticulum (ER)

The endoplasmic reticulum is a network of membrane-enclosed tubules and sacs (cisternae) that extends from the nuclear membrane throughout the cytoplasm.

Occurence:

They occur in all kinds of cell except bacterial and erythrocytes of mammals.

Composition:

• It is composed of lipid protein molecules.
• Also it is non-stable or fixed structure.
• It breaks up, reforms and regroups in response to cellular activities
• ER undergoes partial fragmentation at the time of cell division.
• The entire endoplasmic reticulum is enclosed by a continuous membrane and is the largest organelle of most eukaryotic cells
• Its membrane may account for about half of all cell membranes, and the space enclosed by the ER (the lumen, or cisternal space) may represent about 10% of the total cell volume.

Rough ER

• Description: Studded with ribosomes, giving it a rough appearance.
• Function: Synthesizes proteins that are usually exported from the cell or sent to the cell membrane.
• Location: Found in protein-synthesizing cells like pancreatic cells and salivary glands.

Smooth ER

• Description: Lacks ribosomes and has a smooth appearance.
• Function: Involved in lipid synthesis, metabolism of carbohydrates, and detoxification of drugs and poisons.
• Location: Found in steroid-producing cells like fat cells, liver, and muscle cells.

​

Explore our MDCAT webapp for tests, video lectures, and complete prep resources.