Which of the following statements about chemically-gated ion channels are not true?
A. Their amino acid chains wind back and forth across the membrane. B. They close in response to binding of the signal molecule. C. A pore exists in the center of the protein. D. The pore connects the extracellular fluid with the cytoplasm. E. The pore is big enough for ions to pass through it.
Chemically gated ion channels will open for the specific binding agent, not close for it. This is the false statement: they will close in response to binding of the signal molecule. An ion channel that is chemically gated is meant to only allow a certain kind of ion through. Potassium and calcium are two examples of ions that have to come through ion channels like this. These ions are too big for the cell membrane to easily let pass through. After all, the membrane is semi-permeable to the small ions that come in and out of a cell.
Ion channels have to allow only one specific item in. Otherwise, the cell is taking in too many things. If the channel closed for certain binders, it would let in too many items. Only opening for certain binding agents avoids this.