Which of the following is NOT one of the four main elements of an amino acid? A) Carbon
B) Hydrogen
C) Calcium
D) Nitrogen
E) Oxygen

CALCIUM

Amino acids are organic molecules that, when linked together with other amino acids, form a protein. Amino acids are essential to life because the proteins they form are involved in virtually all cell functions. Some proteins function as enzymes, some as antibodies, while others provide structural support. Although there are hundreds of amino acids found in nature, proteins are constructed from a set of 20 amino acids. Generally, amino acids have the following structural properties:

A carbon (the alpha carbon)

A hydrogen atom (H)

A Carboxyl group (-COOH)

An Amino group (-NH2)

A "variable" group or "R" group

All amino acids have the alpha carbon bonded to a hydrogen atom, carboxyl group, and amino group. The "R" group varies among amino acids and determines the differences between these protein monomers. The amino acid sequence of a protein is determined by the information found in the cellular genetic code. The genetic code is the sequence of nucleotide bases in nucleic acids (DNA and RNA) that code for amino acids. These gene codes not only determine the order of amino acids in a protein, but they also determine a protein's structure and function.