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4.4.1.1. Primary structure of proteins

Primary structure of proteins

The primary structure is the linear sequence of amino acids in the protein, ordered from the first amino acid to the last. Therefore, it indicates the amino acids that make up the polypeptide chain and in what order they are found. The function of each protein depends on its sequence of amino acids that make it up and the form it takes.

All proteins have two ends:

  • An N-terminal end in which the first amino acid with its free amino group is found , which is why it is called the N-terminal amino acid.
  • C-terminal end, in which the last amino acid with its free carboxyl group is located , which is why it is called the C-terminal amino acid .

The sequence of a protein is defined by listing the amino acids from the N-terminus to the C-terminus. This sequence is based on the information provided by DNA, and the function of the protein depends on it and determines the rest of the more complex structural levels.

A characteristic of this structure is its zigzag arrangement, due to the rotational capacity of the bonds that form the α-carbon. The peptide bonds can not rotate and the atoms of carbonnitrogen and oxygen involved in them are in the same plane.

Although there are only 20 different amino acids that make up peptides, as they can have hundreds or thousands of amino acids, the variety of peptide sequences is practically unlimited, since 20n different polypeptides can be formed, where n is the number of amino acids present in the chain.

Fundamental ideas about the primary structure of proteins

The primary structure is the linear sequence of amino acids in the protein, linked by peptide bonds between the carboxyl group (-COOH) of one amino acid and the  amino group (-NH2) of the next amino acid.

If the protein is denatured, the primary structure is not lost. The amino acid sequence remains.