Answer :
The myoglobin protein, which carries oxygen in muscle cells, has only the first three levels of protein structure . Myoglobin is made up of only one polypeptide chain.
A polypeptide chain is a collection of amino acids joined together covalently by peptide bonds. Backbone representations make it easiest to see how proteins are organized into chains. Peptide refers to a brief polypeptide of 50 amino acids or fewer. A polypeptide is a non-branched, continuous chain of amino acids that is bonded together by peptide bonds. By joining the carboxyl group of one amino acid to the amine group of the following amino acid, the peptide bond creates an amide. Protein polypeptide chains are linear polymers constructed from a set of 20 different standard amino acids that are bonded together from the N-terminus to the C-terminus by peptide bonds. Each amino acid has a side chain, or R group, that serves as a fingerprint of its identity.
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