Pharmacognosy - medicinal plants (herbs)

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Proteins structure and composition

Protein structure. Basic structural unit of proteins. Amino acid, symbol, chemical name. Levels of protein structure.

The structural basic composition of the proteins are carbon, hydrogen, oxygen and nitrogen.

Often, may also be present the sulfur and phosphorus. Other occasional elements are iodine, copper, iron and zinc.

Nitrogen is the characteristic element constituting about 16% of most proteins and is the atom that is used for its analytical determination.

The structural unit of proteins are amino acids of which about 20 are actually involved in its constitution.

These molecular structures have at least one carboxylic group and an α-amino group.  From these simple structures is formed a long chain of amino acids linked by hydroxyl groups endings with the subsequent amine hydrogen in a configuration which only supports the L-enantiomorphs.

The polymers so formed are called peptides and are the protein constituents.


The amino acids in proteins

See: The amino acids that form proteins.

Proteins are macromolecules containing amino acids ranging from 30 to 10.000 and depending on the various bonds are divided into four levels of composition:

  • Primary: determined by the sequence of the constituent amino acids.
  • Secondary: they are folded polypeptide chains organized into blocks in a spiral.
  • Tertiary: Arrangement of the folded chains in layers.
  • Quaternary: Levels of organization comprising the previous formations and finally determines the specific function of the protein in the biological process. With the loss of this structure by some external agent, the protein is denatured.

Finally it is conceivable a fifth level, considering the clustering of several proteins into macromolecules complex structures, involved in anabolic processes of fatty acids and electron transport.

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