Some of the primary functions of proteins include their enabling the biochemical reactions that help digest food and respond to stimuli, replicating DNA and providing the structural building blocks for muscles, skin and other tissues. Acting as catalysts, enzymes are the protein-based molecules that play an important role in a wide range of organic processes. Proteins also help to transport nutrients and vital substances, one example being hemoglobin, which transports oxygen throughout the bloodstream.
Proteins represent an essential element of all living organisms and are involved in almost all of the processes occurring within cells. They are differentiated from each other mainly by the sequence of amino acids in their structure. Their structure is genetically dictated and often results in the folding of the protein into a three-dimensional form, which is best suited to its specific function.