Primary, Secondary tertiary and quartenary structures of proteins

Proteins can be defined as biological polymers that are essentially made up of amino acids. If several amino acids are linked to each other by peptide bonds, then the chain of amino acids formed is called a polypeptide chain. Several polypeptide chains twisted together in a 3-dimensional shape form a structure known as protein. Proteins are often seen to have a complex structure that involves several, curves, loops, and folds. Folding occurs spontaneously in proteins. Chemical bonding present between polypeptide chain portions helps in holding the protein together and thereby giving it a particular shape. Proteins are of four main structures namely Primary, Secondary, tertiary, and Quaternary structures of protein, and are distinguished according to their complexity in the polypeptide chain. 

Primary Structures of protein

The primary structure of a protein is defined as the distinctive order in which several amino acids are linked to one another to produce a particular type of protein. Mostly the protein structures are constructed from a group of 20 amino acids. Primary structures of protein normally have the following properties. 

Carbon is an α carbon that is bonded to 4 following groups:

• An (-NH2) group or nitro group
• An atom of hydrogen (H)
• An “R” group “variable” group
• A particular Carboxyl group (-COOH)

In all amino acids, it can be seen that the alpha carbon is bonded to a carboxyl group, amino group, and hydrogen atom. The variation of “R” groups occurs within amino acids and specifically finds the difference between various protein monomers. The sequence of amino acids within a protein is decided by the data obtained in the genetic code of the cell. 

Secondary Structures of protein

The secondary structure of a protein is defined as the folding or coiling of a polypeptide chain that provides the protein with its 3-dimensional shape. Two basic types of secondary structures are generally observed in the case of proteins. The first one is known as the α (alpha) helix structure. This particular structure looks like a coiled spring. Further, it is secured through Hydrogen bonding within the polypeptide chain. The second one is known as the β (beta) pleated sheet. This particular structure is seen to be pleated or folded. Further, they are held together through hydrogen bonding between units of polypeptide within the folded chain, lying adjacent to each other. 

Tertiary Structures of protein

The tertiary structure of a protein is defined as the comprehensive 3 –dimensional structure of the polypeptide chain within a particular protein. Various types of forces and bonds are present that hold the tertiary structure of a protein. These have been discussed in the following.

• Hydrogen bonding within the “R” groups amino acids and the polypeptide chain helps in stabilizing the overall protein structure by holding the specific protein in a particular shape via hydrophobic interaction. 
• Hydrophobic interaction highly contributes to the shaping as well as folding of a particular protein. The amino acid’s “R “ group is the group that is either hydrophilic or hydrophobic. The hydrophilic “R” group amino acids will seek to establish contact with their surrounding aqueous medium. On the other hand hydrophobic “R” groups amino acids will try avoiding water thereby positioning themselves at the protein center. 
• Ionic bonding is seen to occur due to the folding of protein between negatively charged groups of “R” and positively charged groups of “R”. This helps them to achieve close contact with each other. 

Quaternary Structures of protein

The quaternary structure of the protein is defined as the macromolecule protein structure formed due to interactions between several polypeptide chains is known as a sub-unit. Quaternary structures of protein may involve multiple protein subunits of the same type. At the same time, they can also be composed of varying subunits. For instance, Haemoglobin is a protein that has a quaternary structure. Hemoglobin that is particularly present in blood can be defined as a protein that particularly contains iron and binds together the molecules of Oxygen. It essentially contains four subunits: 2 β subunits and 2 α subunits. 

Conclusion

Throughout the article, the four main structures of protein namely Primary, Secondary, tertiary, and Quaternary structures of protein have been discussed. Structures of protein are an important concept in Biochemistry and have a wide range of applications. Under this core topic, an individual discussion has been done on Primary structures of protein, secondary structures of protein, tertiary structures of protein, and Quaternary structures of protein.