Aprotein channel is a transport protein that a. always moves substances against a concentration gradient. b. pumps ions out of a cell. c. serves as a tunnel for specific substances. d. always requires energy from the cell.

Protein and polypeptide sequences can be determined by first partially hydrolyzing the protein or polypeptide followed by amino acid sequencing of the fragment pieces using the chemical degradation process known as edman degradation. determine the sequence of the initial (18-amino acid) polypeptide that produces the following five partial sequences after hydrolysis and edman degradation.