Protein By Definition
To know what is protein could be of great importance in order to understand how the cells function. Proteins are one of the three most important classes of large biological molecules – nucleic acids, proteins and carbohydrates. Protein consists of one or more than one chain of amino acid residues. To understand what is protein, one must know what is their structure, how they are synthesized, which are their primarily functions and particularly how they participate in the metabolism processes. The protein structure defines the protein primary function and determines the uniqueness of each protein. The specificity of the protein structure is dictated by the nucleotide sequence of corresponding genes which defines the actual amino acid sequence and composition. The order of amino acids and their interaction results in specific folding of the protein and determines a particular three-dimensional structure that defines its activity. Proteins have many different functions within living organisms on cellular, system and organism level – regulation of biological processes; molecular transport; catalyzing metabolic reactions; responding to stimuli and many others.
What Is Protein Bio-polymer?
The main building blocks of proteins are 20 L-α-amino acids. All proteins consist one or more polymer chains of amino acids. All amino acids which build proteins have the three common structural features:
- an α-carbon to which an amino group
- a carboxyl group,
- a variable side chain are bonded
The first two determine the building of a repeatable and identical bonds between the amino acids, called peptide bond. When it becomes part of a protein chain, a single amino acid is called an amino acid residue or just residue. The single residues are linked to each other with series of carbon, nitrogen, and oxygen atoms known as protein backbone. While the side chains of the standard amino acids are quite variable in chemical structures and properties, which determines the specifics of the physico-chemical properties of the amino acids residues. As proteins are linear biopolymers, their two ends could be easily distinguished – the protein end with a free carboxyl group is denoted as the carboxy- or C-terminus, while the other end with a free amino group is known as the amino- or N-terminus. The interaction of the amino acid side chains determines protein 3D-structure and its overall biochemical function.
The understand what is protein, polypeptide, or peptide one should capture the specifics of the term meaning and also to put in the particular context. The term protein is preferred in the cases when the complete biological molecule is in a stable conformation, while peptide is generally used when the molecule is a short amino acid oligomers (up to 20–30 residues) often without stable 3D-structure. The term polypeptide stays in between – a variable in length sequence of amino acids, which does not have a defined conformation.