question: There are 20 different common amino acids needed to make what organic compound?
distractor3: cells
distractor1: lipids
distractor2: nutron
correct_answer: proteins
support: Proteins are organic compounds that contain carbon, hydrogen, oxygen, nitrogen, and, in some cases, sulfur. These compounds may many essential functions within the cell (see below). Proteins are made of smaller units called amino acids . There are 20 different common amino acids needed to make proteins. All amino acids have the same basic structure, which is shown in Figure below . Only the side chain (labeled R in the figure) differs from one amino acid to another. These side chains can vary in size from just one hydrogen atom in glycine to a large heterocyclic group in tryptophan. The variable side chain gives each amino acid unique properties. The side chains can also characterize the amino acid as (1) nonpolar or hydrophobic, (2) neutral (uncharged) but polar, (3) acidic, with a net negative charge, and (4) basic, with a net positive charge at neutral pH.