Which statement about the sidedness of the plasma membrane is correct?

• A. Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane.
• B. The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed.
• C. Every integral membrane protein has a specific orientation in the plasma membrane.
• D. The two lipid layers may differ in specific lipid composition.
• E. All of the listed responses are correct.

Answer: (E)

Verified step by step guidance

1. Understand the concept of 'sidedness' of the plasma membrane, which refers to the asymmetrical distribution of components like proteins, lipids, and carbohydrates across the membrane.
2. Recognize that the plasma membrane is composed of two lipid layers, which can have different compositions. This is due to the specific functions and interactions each side of the membrane has with its environment.
3. Consider the orientation of integral membrane proteins. These proteins span the membrane and have specific orientations that are crucial for their function, such as signaling or transport.
4. Examine the process of membrane construction. The asymmetrical distribution of components is established during the construction of the membrane, often in the endoplasmic reticulum and Golgi apparatus, before being transported to the plasma membrane.
5. Conclude that all the statements provided are correct, as they each describe a different aspect of the sidedness and functional asymmetry of the plasma membrane.