Question 2
A cell biologist compared the properties of rough endoplasmic reticulum (ER) and smooth ER. She found that one type of ER is used for protein storage, and the other is used for lipid storage. What accounts for this difference?
The difference in function between rough endoplasmic reticulum (ER) and smooth ER is due to their structural differences and the presence of ribosomes.
Rough ER appears rough due to the presence of ribosomes attached to its surface. These ribosomes are responsible for protein synthesis. Rough ER is primarily involved in the synthesis and folding of proteins that are destined to be exported out of the cell or incorporated into the cell membrane. It acts as a storage site for proteins.
On the other hand, smooth ER lacks ribosomes on its surface, giving it a smooth appearance. Smooth ER is involved in various functions, such as lipid metabolism, detoxification of drugs and toxins, and calcium ion storage. It is responsible for synthesizing lipids, including phospholipids, cholesterol, and steroid hormones. It also detoxifies harmful substances by modifying them to be more water-soluble, making them easier to excrete. Additionally, smooth ER plays a role in storing calcium ions, which are important for cell signaling and muscle contraction.
Therefore, the presence or absence of ribosomes on the ER surface accounts for the difference in function between rough ER (protein storage) and smooth ER (lipid storage).