Peptide vs Protein
Amino acids, peptides, and proteins are often referred to as related terms, yet they are different in their characteristics. Amino acids are the building blocks of both peptides and proteins. Amino acid is a small molecule that contains an amino group (-NH2) and a carboxylic acid group (-COOH), which are bound to a central carbon atom, with an additional hydrogen and a side chain (R- group). This side chain varies among all the amino acids; hence it determines the unique characters and the chemistry of each amino acid. Particular gene sequence is used to determine the amino acid sequence in both peptides and proteins.
Peptides are made up with two or more amino acids, linked by peptide bonds and are present as linear chains. The length of a peptide is determined by the amount of amino acids in it. Usually the length of a peptide is less than approximately 100 amino acids.
Prefixes are used to describe the type of peptides in general terminology. For example, when a peptide is made of two amino acids, it is called dipeptide. Like that, three amino acids are combined to yield tripeptides, four amino acids are combined to yield tetrapeptides, etc. Apart from these types, there are oligopeptides (made up of 2-20 amino acids) and polypeptides, which have many peptides (less than 100). The most important characteristic features of peptides are determined by the amount and the sequence of amino acids.
The primary function of the most peptides is to allow effective communication by carrying biochemical messages from one place to another in the body.
Proteins are the most diverse group of biological macromolecules. A protein is composed of one or more long unbranched chains called polypeptides and yet the building blocks of proteins are amino acids. The sequence of amino acid determines the major characteristics of a protein, while this amino acid sequence is defined by the particular gene sequence.
Usually proteins have stable three dimensional structures. These structures can be discussed in terms of a hierarchy of four levels; primary, secondary, tertiary and quaternary. The primary structure is the amino acid sequence of a protein. The secondary structure is produced by forming hydrogen bonds between two nearby amino acids, thus resulting structures called β-plated sheets, and coils called α-helices. The regions of secondary structure are then folded further in space to form the final three dimensional structures of the protein. Arrangement of the multiple polypeptides in space results the quaternary structure of a protein.
The major functions of proteins are enzyme catalysis, defense, transport, support, motion, regulation, and storage.
What is the difference between Peptide and Protein?
• Peptides are short linear chains of amino acids, whereas proteins are very long chains of amino acids.
• Several amino acids are linked together to form a peptide by peptide bonds, while several peptides are linked together to form protein molecules.
• Normally, proteins have stable three dimensional structures. In contrast, peptides are not organized in a stable three-dimensional structure.
• Length of a peptide is less than approximately 100 amino acids, while that of a protein is more than 100 amino acids. (There are exceptions; thus, the differences rely more on the function of the molecules, rather than the their sizes)
• Unlike peptides, proteins are considered as macromolecules.
• In peptides, only side chains of amino acids form hydrogen bonds. Whereas, in proteins, not only side chains, but also peptide groups, form hydrogen bonds. These hydrogen bonds can be with water or with other peptide groups.
• All the peptides exist as linear chains while proteins can exist as primary, secondary, tertiary, and quaternary.