Types of Protein: Structure, Function and Classification (original) (raw)

Last Updated : 23 Jul, 2025

**Proteins are large and complex biomolecules made up of long chains of amino acid residues that play a crucial role in cells. They are essential in our day-to-day life for good health and benefit in growing something faster. Proteins are made up of smaller units called amino acids. The protein consists of hydrogen, carbon, oxygen, sulfur, and nitrogen.

Table of Content

• What is Protein?
• Protein Structure Hierarchy
• Importance of Protein
• Classification of Protein
• Function of Protein
• Conclusion - Proteins
• FAQ's - Proteins

What is Protein?

**Proteins are very complex molecules involved in some chemical processes that are important for life. Protein is made of small units of amino acids. These proteins help in metabolism, communication, and movement in our body.

**Also Read: Difference Between Globular and Fibrous Protein

**Protein Structure Hierarchy

There are four levels in the structural hierarchy of proteins. They are:

**Primary Structure of Protein

In the primary structure of proteins, the polypeptide chain are linked together to form a sequence of amino acids called polypeptide chain. The primary structure of this level contains mainly amino acids which are present in the chain. Peptide bonds are present in the primary structure of the protein.

The primary structure of protein is important as it determines the final fold and hence the function of the protein. Any change in the sequence of amino acids completely changes the entire protein.

If two amino acids are there to form a chain of proteins it is called a dipeptide bond. Similarly, if three amino acids are ready to form a link it is called tripeptide.

Characteristics of peptide bond:

• A peptide bond is rigid and planar
• It is not able to charge but it is polar.
• It has a partial double bond character.

**Secondary Structure of Protein

This secondary structure of proteins contains a folding structure polypeptide chain. The secondary structure is formed by the H-bonds. It is formed mostly with the alpha helix and beta pleated sheets. Example: Myoglobin.

There are some types of secondary structure

• Alpha Helix
• Beta plated sheet
• Strand
• Loops

**Tertiary Structure of Protein

The tertiary structure of proteins is in the form of a 3-dimentional structure of the monomeric and multimeric structures. This 3D structure of a polypeptide is simply called the tertiary structure of the protein. This tertiary structure is because of the lowest energy and greatest stability state of the polypeptide chain. The structure came from folding secondary structure of the protein.

Function of tertiary structure is that it has a unique function like interacting with other molecules.

**Quaternary Structure

The quaternary structure of proteins is in the form of a 3-Dimensional structure of macromolecules which is a combination of individual polypeptide chains. This quaternary structure is also formed from a special combination of tertiary structures. Quaternary structure is also known as oligomeric proteins. Example: Hemoglobin

Functions of quaternary structure:

• It helps in the chromosome replication process.
• It helps in metabolism

Also Read: Protein Structure

**Importance of Protein

• Protein helps in maintaining good shape and fit for our body.
• Protein repairs the body's damaged tissues.
• Protein is used to build bones, skin, and muscles.

**Classification of Protein

Classification of proteins is based on the

• Based on the shape
• Based on Constitution
• Based on the Nature of molecules

**Based on shape

• Fibrous protein
• Globular proteins

**Based on the constitution

• Simple proteins
• Conjugated proteins

**Based on nature of molecules

• **Acidic proteins: They exist as anion and contain acidic amino acids. Example of acidic protein is **Alpha-synuclein.
• **Basic proteins: They exist as cations and are rich in basic amino acids. Example of acidic protein are lysine, arginine etc.

The Basic Unit of Protein - Amino Acids:

Amino acids are the basic structural unit of protein. Amino acids consist of the carbon atom, a carboxyl group (COOH), and a hydrogen atom.

Amino acids are classified as follows:

• **Aromatic: Tyrosine, Tryptophan, Phenylalanine.
• **Positively charged: Lysine, Arginine, Histidine.
• **Negatively charged: Aspartate, Glutamate.
• **Nonpolar, aliphatic: Leucine, Methionine, Isoleucine.

Function of Protein

**Enzymatic protein

The function of enzymatic protein:

• It accelerates the metabolic process in our cells.
• It also accelerates the metabolic process in stomach digestion, liver functions, and blood clotting.

**Hormonal protein

The function of hormonal protein

• Hormonal proteins are protein-based chemicals secreted by endocrine glands.
• By using hormonal protein each hormone affects particular cells in the body.

**Structural protein

The function of structural protein

• Structural proteins are very important for the body because they are fibrous proteins.
• It helps in developing muscles, bones, skin, and cartilage.

**Defensive protein

The function of defensive protein

• These defensive proteins help in developing antibodies for attacking.
• These antibodies are developed in white blood cells to attack bacteria.

**Storage protein

The function of storage protein

• Storage protein stores minerals like potassium.
• Storage protein contains ovalbumin and casein found in milk, and egg whites.

**Transport protein

The function of transport protein

• Transport protein called calbindin which is useful for absorption of calcium from intestinal walls.
• Transport proteins carry important materials to the cells of the body.

**Receptor protein

The function of receptor protein

• It controls the substances which enter and leave the cells.

**Contractile protein

The function of contractile protein

• It helps in regulating the strength, speed of the heart, and muscle contractions.
• Contractile proteins cause heart complications if the heart produces severe contractions.

Conclusion - Proteins

Proteins are complex biomolecules which are the building blocks of living organisms. The protein consist of amino acids. The proteins are classified on: basis of shape, constitution, and nature of molecule. The protein structure has hierarchy of four levels i.e. primary structure, secondary structure, tertiary and quaternary structure.