Lysine
Overview
Lysine is an α-amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 HO2CCH(NH2)(CH2)4NH2. It is an essential amino acid
Essential amino acid
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...

, which means that the human body cannot synthesize it. Its codons are AAA and AAG.

Lysine is a base, as are arginine
Arginine
Arginine is an α-amino acid. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that codify for arginine during...

 and histidine
Histidine
Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

. The ε-amino group often participates in hydrogen bonding and as a general base in catalysis
Catalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....

. (The ε-amino group, which is attached to the NH3+ group, is the fifth carbon down from the α-carbon, which is attached to the carboxyl (C=OOH) group.)

Common posttranslational modification
Posttranslational modification
Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis, and thus gene expression, for many proteins....

s include methylation of the ε-amino group, giving methyl-
Methyllysine
In proteins, the amino acid residue lysine can be methylated once, twice or thrice on its terminal sidechain ammonium group.Such methylated lysines play an important role in epigenetics; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding...

, dimethyl-
Methyllysine
In proteins, the amino acid residue lysine can be methylated once, twice or thrice on its terminal sidechain ammonium group.Such methylated lysines play an important role in epigenetics; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding...

, and trimethyllysine
Methyllysine
In proteins, the amino acid residue lysine can be methylated once, twice or thrice on its terminal sidechain ammonium group.Such methylated lysines play an important role in epigenetics; the methylation of specific lysines of certain histones in a nucleosome alters the binding of the surrounding...

.
 
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