Membrane-bound organelles consisting of flattened membranous sacs called cisternae with ribosomes on the surface
The Correct Answer and Explanation is:
The organelle you’re referring to is the rough endoplasmic reticulum (rough ER). It consists of a network of flattened membranous sacs known as cisternae, with ribosomes attached to its outer surface, giving it a “rough” appearance.
Structure of Rough ER:
The rough ER is continuous with the outer nuclear membrane and is composed of a series of interconnected tubules and flattened sacs (cisternae). The ribosomes on the cytoplasmic side of the rough ER are key to its function, as they are the sites of protein synthesis. These ribosomes translate mRNA into proteins, which are then inserted into the lumen (interior) of the rough ER or pass through it into other parts of the cell.
Function of Rough ER:
- Protein Synthesis: The rough ER is primarily involved in the synthesis of proteins that are either secreted from the cell, incorporated into the cell’s plasma membrane, or sent to an organelle called the lysosome. The proteins synthesized on the rough ER ribosomes often undergo initial folding and modifications, like the addition of carbohydrate groups, which are essential for their final function.
- Protein Folding and Quality Control: After proteins are synthesized in the rough ER, they are often folded into their proper shapes with the help of chaperone proteins. Misfolded proteins are often targeted for degradation to prevent them from causing cellular damage.
- Lipid Synthesis: Although the rough ER is mainly known for protein synthesis, it also plays a role in lipid metabolism, which is important for membrane formation and maintenance.
Relationship with the Smooth ER:
The rough ER is often linked to the smooth ER, which lacks ribosomes. The smooth ER is involved in lipid synthesis and detoxification processes. Together, the rough and smooth ER contribute to cellular homeostasis, protein processing, and membrane production.
Thus, the rough ER’s structure and ribosome presence are crucial for its function in synthesizing, modifying, and transporting proteins within eukaryotic cells.
