A cell's ability to respond to external signals is compromised due to a defect in its glycoproteins. What might be the underlying issue?

• A. The glycoproteins are involved in energy production instead of signaling.
• B. The glycoproteins are overexpressed, leading to excessive signaling.
• C. The glycoproteins are degraded too slowly.
• D. The glycoproteins are unable to properly bind to signaling molecules.

Answer: (D)