Proteins Structure

Introduction

Egg whites include huge amounts of proteins known as albumins, and albumins typically have a distinct three-dimensional shape as a result of the formation of links between different amino acids in the protein. As a result of the heating, these connections are broken, exposing hydrophobic (water-hating) amino acids that were previously hidden on the inside of the protein1,2. While trying to get away from the water surrounding them in the egg white, the hydrophobic amino acids will attach to one another, resulting in the formation of a protein network that provides the egg white structure while also rendering it white and opaque.

The formation of a peptide bond (-CO-NH) between the amine group of one molecule and the carboxyl group of the next molecule is followed by the elimination of a water molecule from the reaction. In all other respects, this is an amide linkage. When peptide bonds are formed between amino acids that are more than 10 amino acids in length, the resulting polypeptide chain is formed. When the mass of a polypeptide chain exceeds 10000u and the number of amino acids in the chain exceeds 100, we get what is known as a protein.

The structure of a protein is critical to its ability to perform its job. In order to comprehend how a protein achieves its final shape or conformation, we must first comprehend the four stages of protein structure: primary, secondary, tertiary, and quaternary structure.

Primary structure

• The primary structure of proteins is defined as the precise arrangement of amino acids that comprise their chain.
• The precise sequence of proteins is critical because it influences the final fold and, consequently, the function of the protein once it is synthesised.
• Proteins are formed through the association of a large number of polypeptide chains. These chains include amino acids that have been organised in a precise sequence that is distinctive to the individual protein in question. Any alteration in the sequence of a protein has an impact on the entire protein.

The amino acid sequence contained inside the polypeptide chain is critical for the proper functioning of the protein. This sequence is encoded in the genetic code of the DNA molecule. A mutation in the DNA that results in a change in the amino acid sequence may have an effect on the protein’s ability to function. The amino acid sequence in a protein’s polypeptide chain serves as the protein’s primary structural element. To imagine proteins as Christmas tree ornaments, their main structure could be thought of as the order in which different forms and varieties of popped maize are strung together to form a Christmas tree garland.

The primary structure of a protein is maintained by covalent peptide bonds, which are formed between amino acids and connect them. The main insulin structure, which was the first protein to be sequenced.

Biochemists frequently list the amino acids that begin at the amino-terminus of polypeptide chains as a matter of habit.

All known genetic illnesses, such as cystic fibrosis, sickle cell anaemia, albinism, and others, are produced by mutations that create changes in the primary protein structures, which in turn generate changes in the secondary, tertiary, and most likely quarterly protein structures.

Amino acids are tiny chemical compounds made up of a chiral carbon and four substituents, which are bonded together. Only the fourth amino acid has a side chain that differs from the other amino acids.

Secondary Structure of Protein

In the case of proteins, secondary structure refers to the folded structures that develop within a polypeptide as a result of interactions between atoms in the backbone.

• Proteins do not exist as simple chains of polypeptides, as is commonly believed.
• The interaction between the amine and carboxyl groups of the peptide link is usually responsible for the folding of these polypeptide chains.
• The structure is the shape in which a long polypeptide chain can be found.
• They are found to occur in two main sorts of structures: helix structures and pleated sheet structures. Helix structures are the most common type of structure.
• This structure is formed as a result of the regular folding of the polypeptide chain’s backbone, which is caused by hydrogen bonding between the -CO group and the -NH group of the peptide link.
• On the other hand, parts of the protein chain may develop their own local fold, which is more simpler and commonly takes the shape of a spiral, an expanded shape, or a loop. This is known as a local fold. Secondary elements are local folds that contribute to the formation of the protein’s secondary structure.

(a) α – Helix:

The helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw, with the -NH group of each amino acid residue hydrogen-bonded to the -CO of the adjacent turn of the helix. The helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right-handed screw. The polypeptide chains formed a right-handed screw as a result of the twisting.

(b) β – pleated sheet:

It is in this configuration that the polypeptide chains are stretched out next to one another and then connected to one another by intermolecular hydrogen bonds. Throughout this structure, all peptide chains are stretched out to nearly their maximum extension before being stacked on top of one another, which is held together by intermolecular hydrogen bonds. The pleated folds of draperies are reminiscent of the structure of the pleated sheet, which is why it is called as a pleated sheet.

Tertiary Structure of Protein

• This structure is formed as a result of the protein’s secondary structure being folded more tightly.
• H-bonds, electrostatic forces, disulphide connections, and Vander Waals forces all work together to maintain the stability of this crystal structure
• The tertiary structure of proteins represents the overall folding of the polypeptide chains, as well as the folding of the secondary structure farther down the line.
• It is responsible for the formation of two primary molecular shapes: fibrous and globular.
• Hydrogen bonds, disulphide linkages, van der Waals forces of attraction, and electrostatic forces of attraction are the primary forces that help to maintain the secondary and tertiary structures of proteins.

Quaternary Structure of Protein

In the quaternary structure, the spatial arrangement of various tertiary structures results in the formation of a new structure. Some proteins are made up of two or more polypeptide chains, which are referred to as sub-units, which are linked together. Quinterary structure is the term used to describe the spatial arrangement of these subunits in relation to one another. The exact amino acid sequence of each protein causes it to fold into its own unique and biologically active three-dimensional fold, which is referred to as the tertiary structure in the scientific community. Various combinations of secondary elements make up proteins, some of which are simple and others which are more complex in their compositions. In the case of proteins, domains are segments of the protein chain that have their own three-dimensional fold and can be assigned to a specific function. These are now regarded as the structural and functional building blocks of proteins, both in terms of evolution and function.

Many proteins, the majority of which are enzymes, contain organic or inorganic components that are necessary for their activity and stability in the presence of water. As a result, the study of protein evolution not only provides structural knowledge, but it also serves to link proteins from various sections of the metabolism together.

Conclusion

Proteins are constructed from chains of amino acids, which are subsequently folded into specific three-dimensional configurations. The formation of bonds within protein molecules aids in the stabilisation of their structure, and the final folded forms of proteins are well-suited to their respective roles. Individual proteins are distinguished by their specific shape and structure. Proteins collaborate in a complex and coordinated manner to maintain and support human existence. In other words, understanding the functions of proteins may provide us with clues to the question “What is life?” and closely examining their structures may show how they function.