In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function.
an attachment protein that provides structural support
a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell
a protein involved in enzymatic activity
an active transport protein that moves molecules across a membrane against their concentration gradient
a glycoprotein that is involved in cell-cell recognition