Native proteins are proteins that have their functional three-dimensional structure, which is necessary for their biological activity. They are in their natural, folded state with specific secondary, tertiary, and quaternary structures that are stabilized by various forces such as hydrogen bonding, hydrophobic interactions, and disulfide bonds.
Denatured proteins, on the other hand, are proteins that have lost their natural structure due to the disruption of these stabilizing forces, often due to changes in temperature, pH, or chemical treatment. Denaturation results in the unfolding of the protein, causing it to lose its biological function.