Which of the following statement(s) is/are true concerning carrier proteins?

b. Conformational changes in the membrane protein occur between the conducting and the nonconducting states 

c. A channel-type carrier protein has two states—closed and open

Most transport proteins appear to function as carriers, rather than channels. Important distinctions can be made between types of carrier proteins on the basis of transport kinetics. Two primary types can be distinctly identified based on carriertype and channel-type mechanisms. The most important difference between the channel mechanism and the carrier mechanism is the role in the transport event played by conformational changes in the membrane protein. The channel is depicted as having two states, closed and open, so that it operates like a switch. In contrast, carrier transport is envisioned as requiring a cycle of conformational changes. The transport of one molecule of substrate requires one complete cycle of the protein. In a channel mechanism, binding sites within the open pore are equally accessible from either side of the membrane, whereas in a carrier mechanism, the binding site is available only one side of the membrane at any instant.