 Most proteins consist of linear polymers built from series of up to 20 different L @-@ α @-@ amino acids . All proteinogenic amino acids possess common structural features , including an α @-@ carbon to which an amino group , a carboxyl group , and a variable side chain are bonded . Only proline differs from this basic structure as it contains an unusual ring to the N @-@ end amine group , which forces the CO – NH amide moiety into a fixed conformation . The side chains of the standard amino acids , detailed in the list of standard amino acids , have a great variety of chemical structures and properties ; it is the combined effect of all of the amino acid side chains in a protein that ultimately determines its three @-@ dimensional structure and its chemical reactivity . The amino acids in a polypeptide chain are linked by peptide bonds . Once linked in the protein chain , an individual amino acid is called a residue , and the linked series of carbon , nitrogen , and oxygen atoms are known as the main chain or protein backbone . 
 Most proteins consist of linear polymers built from series of up to 20 different L @-@ α @-@ amino acids . All proteinogenic amino acids possess common structural features , including an α @-@ carbon to which an amino group , a carboxyl group , and a variable side chain are bonded . Only proline differs from this basic structure as it <a href='uninflect' title='1'><mark>contains</mark></a> an unusual ring to the N @-@ end amine group , which <a href='uninflect' title='2'><mark>forces</mark></a> the CO – NH amide moiety into a fixed conformation . The side chains of the standard amino acids , detailed in the list of standard amino acids , <a href='got' title='3'><mark>have</mark></a> a great variety of chemical structures and properties ; it is the combined effect of all of the amino acid side chains in a protein <a href='null_relcl' title='4'><mark>that</mark></a>ultimately <a href='uninflect' title='5'><mark>determines</mark></a> its three @-@ dimensional structure and its chemical reactivity . The amino acids in a polypeptide chain are linked by peptide bonds . Once linked in the protein chain , an individual amino acid is called a residue , and the linked series of carbon , nitrogen , and oxygen atoms are known as the main chain or protein backbone . 
Most proteins consist of linear polymers built from series of up to 20 diffrent L @-@ α @-@ amino acids . alll proteinogenic amino acids possess common structural features , including an α @-@ carbon to which an amino group , a carboxyl group , and a variable side chain r bonded . Only proline differs from this basic structure as it contain an unusual ring to da N @-@ end amine group , which force tdaCO – NH amide moiety into a fixed conformation . The side chains of the standard amino acids , detailed in the list of standard amino acids , got a great variety of chemical structures and properties ; it is the combined effect of all of the amino acid side chains in a protein ultimately determine its three @-@ dimensional structure and its chemical reactivity . The amino acids in a polypeptide chain arrinked by peptide bonds . Once linked in thdarotein chain , an individual amino acid is called a residue , and the linked series of carbon , nitrogen , and oxygen atoms are known as the main chain or protein backbone .