The answer would be D, the carbon-12 atom.
To solve this, you would need to identify the number of amino acids (20) you are dealing with and the number of positions (8) that are available in your polypeptide. so that would come out to 20 x 20 x 20 x 20 x 20 x 20 x 20 x 20 = 20^8
Phosphate, Nitrogen, & Nucleotides
Explanation:
Carrier proteins are proteins that carry substances from one side of a biological membrane to the other.