Membrane carrier proteins differ from membrane channel proteins by which of the following characteristics?
a. Carrier proteins can mediate active transport, while channel proteins cannot.
b. Carrier proteins are glycoproteins, while channel proteins are lipoproteins.
c. Carrier proteins do not bind to the material transported, while channel proteins do.
d. Carrier proteins transport molecules down their electrochemical gradient, while channel proteins transport molecules against their electrochemical gradient.
e. Carrier proteins are synthesized on free cytoplasmic ribosomes, while channel proteins are synthesized on ribosomes bound to the endoplasmic reticulum.