General Index
Aminoacids: Chemical Structure
We classify the aminoacids according to their chemical structure:
We also present in this demo the structure of some Non-protein Aminoacids,
either Metabolic Intermediates or Postranslational modifications.
The models appear in their most usual ionic form at pH 7.4, that is, as zwitterion,
with the groups -NH3+ and -COO- in ionic form.
Neutral of Aliphatic Aminoacids
These aminoacids have an aliphatic hydrocarbon side chain. We also include in this
group Glycine, the simplest of all, whose side chain is a hydrogen atom:
Index
Aromatic Aminoacids
These aminoacids have an aromatic side chain: benzene in Phenylalanine,
a phenol group in Tyrosine and an indol group in Tryptophan.
Index
Hydroxyaminoacids
These aminoacids have al alcohol group in the side chain.
Index
Thioaminoacids
Their side chains contain sulfur.
Index
Secondary amines
The a-amino group is substituted by the side chain. There is only one,
Proline.
Index
Dicarboxylic aminoacids and their amides
They have a carboxyl -COOH or an amide -CONH2 group in the side chain:
Index
Dibasic Aminoacids
They present a basic group in the side chain; Amino- in Lysine, guanidino- in Arginine and imidazol- in Histidine
Index
Non-protein Aminoacids
Some metabolic intermediates and some neurotransmitters have an aminoacid structure but
they don't appear in proteins. They are called Non-protein Aminoacids.
As metabolic intermediates, we have Ornithine, Citrulline, Homocysteine and Homoserine:
And Dihydroxyphenylalanine (DOPA), metabolic precursor of catecholamines, thyroid hormones and melanin:
we also know the so-called w-aminoacids (omega-aminoacids),
in which the amino group substitutes the last carbon atom in the chain instead of a-carbon.
For example, b-Alanine and
g-Aminobutyric Acid (GABA), inhibitory neurotransmitters in the Central
Nervous System.
Some aminoacids are chemically modified after being integrated in the polypeptide
chain, and sometimes appear in protein hydrolysates. They are Postranslational modifications,
because the modification takes place after the process of Translation or Protein Synthesis.
Very often appears in protein hydrolysates Cystine, that is formed from two
cysteines linked by a disulfide bond:
In Collagen we find many residues of 4-Hydroxyproline and 5-Hydroxylysine:
Some blood coagulation factors present a postranslational modification consisting in
the carboxylation of glutamic acid residues, giving g-Carboxiglutamic Acid.
This modification provides additional negative charge to those factors, like Prothrombin.
Index