Which of the following is NOT a function of membrane proteins? cell identity markers enzymes neurotransmitters receptors structural support

To determine which option is NOT a function of membrane proteins, let's analyze each choice:

1. Cell Identity Markers: Membrane proteins can act as cell identity markers by displaying specific carbohydrates that help distinguish one cell type from another.

2. Enzymes: Many membrane proteins function as enzymes, catalyzing specific biochemical reactions at the membrane surface.

3. Neurotransmitters: Neurotransmitters are chemical messengers released by neurons; they are not membrane proteins but rather bind to membrane receptors to elicit a response.

4. Receptors: Membrane proteins often function as receptors, binding to signaling molecules and initiating a cellular response.

5. Structural Support: Membrane proteins provide structural support to the cell, helping maintain its shape and organization.

Conclusion

Thus, the choice that is NOT a function of membrane proteins is neurotransmitters. Neurotransmitters are released by neurons and received by membrane receptors, but they themselves are not part of the membrane.