Question

which three components are common to all amino acids?
an amino group, a carboxyl group, and an r group
an amino group, a phosphate group, and an r group
a five-carbon sugar, a phosphate group, and a nitrogenous base
a five-carbon sugar, an amino group, and a nitrogenous base

Explanation:

To determine the three components common to all amino acids, we recall the structure of an amino acid. An amino acid has a central carbon atom bonded to an amino group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), a hydrogen atom, and an R - group (which varies among different amino acids).

• Option 1: "an amino group, a carboxyl group, and an R group" matches the structure of an amino acid.
• Option 2: A phosphate group is not a component of an amino acid (phosphate groups are part of nucleotides or phospholipids, for example).
• Option 3: A five - carbon sugar, a phosphate group, and a nitrogenous base are the components of a nucleotide (the building block of nucleic acids like DNA and RNA), not an amino acid.
• Option 4: A five - carbon sugar and a nitrogenous base are nucleotide components, and they are not part of the amino acid structure.

Answer:

A. an amino group, a carboxyl group, and an R group