What is a Polypeptide?

by Kevin Cunningham - Posted 11 months ago

What is a Polypeptide?

A polypeptide is an unbroken sequence of amino acids linked together by peptide bonds. The peptide bond binds the carboxyl group of one amino acid to the amine group of the following amino acid to form an

Proteins are significant in biology because they are the building blocks of bones, hair, and nails, as well as enzymes, antibodies, muscles, connective tissue, and many other things. Peptides vary from polypeptides because they are composed of shorter amino acid chains. 

Structure of a Polypeptide

Proteins are made up of one or more polypeptide chains. Each polypeptide chain is composed of smaller sub-units or amino acids linked together. Polypeptides are protein building blocks, and amino acids are polypeptide building units.

Consider an amino acid to be a paper clip. A paper clip chain is made by connecting many paper clips. Hundreds of amino acids are joined together to create a polypeptide chain. A polypeptide chain can operate as its protein. On the other hand, many proteins are constructed from several polypeptide chains. 

Formation of Polypeptides

Polypeptides are formed in the presence of water. Each amino acid has an amino group. The letters NH2 denote an amino group, where N represents nitrogen and H stands for the hydrogen. Amino acids have a carboxyl group that looks like COOH.

Carbon, oxygen, and hydrogen are represented by the letters C, O, and H, respectively. When the polypeptide is formed, at least two amino acids saddle up next to one another. When they do so, they reach out to one another.
The amino group reaches out to the other, but the carboxyl group does not. They chemically connect their hands to form a peptide bond, a covalent relationship between two amino acids. After holding someone's
hand for too long, we've all noticed how a coating of light sweat accumulates between the fingers.

Water is produced when two amino acids join their hands to create a peptide bond. Condensation occurs when two or more molecules combine to make an even bigger molecule while simultaneously releasing a smaller one.

The amino acid with the carboxyl end gives out an OH, whereas the amino acid with the amino end gives off an H. OH + H = H2O, which is the same as water.

Function of Polypeptides

Proteins and peptides are crucial biological components that perform critical functions in cells. Proteins give cells their shape and respond to external signals. Peptides have a vital role in modulating the action of other drugs.

Proteins and peptides are structurally similar in that they are made up of chains of amino acids held together by peptide bonds (also called amide bonds). Peptides, on the other hand, can be categorized as oligopeptides, which contain a limited number of amino acids, and polypeptides, which have a significant number of amino acids.

Proteins are formed by the joining of one or more polypeptides. Proteins are very long peptides. Some researchers use peptides to refer to oligopeptides or small amino acid chains, whereas polypeptides are proteins or chains of 50 or more amino acids.

Synthesis of Polypeptides

Polypeptide synthesis is a perplexing name because it is also employed in producing oligopeptides and proteins. While these molecules change in several ways, their essential structure - various lengths of amino acid chains - remains the same.

A single amino acid is precisely that: an amino acid. It forms a peptide when it binds with another amino acid. Joined amino acids are all peptides, regardless of how many amino acids are linked together or the structure.

Peptides are further classified based on their length. Oligopeptides are linear strings of two to twenty amino acids long. A dipeptide (two-bound amino acids) is also an oligopeptide, as is a pentapeptide (five-bonded amino acids), as seen in the figure above.

Polypeptides are linear strings of twenty to fifty amino acids long. These might take the shape of primary or secondary structures. Larger peptides are classified based on their system. Proteins comprise at least fifty amino acids and frequently wrap into different forms.

They are divided into primary, secondary, tertiary, and quaternary structures. A more complicated protein must first exist in the preceding form to be produced.

• The amino acid sequence of a simple peptide chain is referred to as its primary structure.

• Secondary structures, most often alpha-helix, beta-strand, or betasheet, use hydrogen bonds to generate spirals, coils, or sheet shapes from a single polypeptide chain.

• Tertiary structure similarly involves a single polypeptide chain but folds it further to form a globule-like molecule held together by hydrogen bonds and salt bridges, for example.

• Two or more polypeptide chains combine to create a protein with a single function in quaternary structures. The oxygen-carrying molecule in human blood, hemoglobin, is a quaternary protein composed of two pairs of bonded polypeptide chains.

Peptide Bonding

Peptide bonds connect two amino acids in a ribosome. These are chemical linkages formed by the carboxyl group of one amino acid and the amino group of another. When these two residues bind, a single molecule of water is released - a dehydration synthesis process.

To create H20, the carboxyl group loses its negatively charged hydroxyl ion, and the amino group loses a positively charged hydrogen ion. The connected amino acids dehydrate, and water is generated.

Therefore this process is sometimes referred to as a condensation reaction. Because of the loss of ions from newly-linked amino acid molecules, several textbooks state that polypeptides and proteins are
built from amino acid residues.

The ribosome brings the carboxyl group of one amino acid closer to the amino group of the next to generate peptide bonds. Adenosine triphosphate is required to create a peptide bond (ATP).

This reaction may be reversed by adding water; however, breaking a peptide bond in this manner occurs at a considerably slower pace than the dehydration synthesis reaction. This is owing to an additional double
bond in amino acid residues. Enzymes in the body accelerate this response.

Water's -OH ion eliminates the carboxyl's positive charge, loosening the connection. The water molecule's +H ion influences the amino group's negative nitrogen ion.

Both processes disrupt the peptide link and restore both amino acids' full carboxyl and amino groups. Amino acids in a chain should be between twenty and fifty for the polypeptide bond, and the equivalent number of bonds should be between nineteen and forty-nine.


Polypeptide chains are crucial because they are the building blocks of proteins. Proteins are macromolecules that perform a variety of critical tasks within the cell. Proteins are structural components of the cell that include the cytoskeleton. They also produce enzymes, which accelerate chemical processes within the cell.