Final answer:
Voltage-gated ion channels are most likely to be monomeric proteins, as they usually consist of a single protein subunit that forms the channel, while ligand-gated and gap junction channels are generally multimeric, made up of multiple protein subunits.
Step-by-step explanation:
The student asked which of the following types of ion channels is a monomeric protein: Ligand-gated, gap-junction, or voltage-gated. Among these, ligand-gated ion channels are typically multimeric, meaning they consist of multiple protein subunits. In contrast, gap junction channels are formed by the docking of two hemichannels, each composed of six connexin subunits. However, most voltage-gated ion channels are composed of a single protein subunit, or monomer, that has multiple domains to form the channel. Therefore, voltage-gated ion channels are likely to be monomeric proteins. Ligand-gated channels, also known as ionotropic receptors, open in response to a neurotransmitter binding to the receptor, allowing ions like sodium, calcium, and potassium to pass through, which is crucial for the transmission of electrical impulses in nerve and muscle cells.