Two separate polypeptide chains are most commonly covalently linked to each other through disulfide bonds.
A peptide is two or more amino acids that are held together with the help of peptide bonds
A protein chain has two ends: one is the amino terminus (positively charged) and the other one is the carboxy terminus (negatively charged).
Disulfide bonds which are mostly found between the sulfur-containing side chains of cysteines contribute to the formation of the tertiary structure of proteins.
These bonds act like safety pins as they keep the different polypeptide chains held together firmly and give a shape to the protein folding.
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