What are Proteins? [Updated] Structure and classification of Proteins

Structure and Classification of Proteins

The macromolecules occurring in ample amounts in all the cells are called proteins. These units are the most important for living beings. Hundreds and thousands of protein molecules of different sizes constitute a living body. Proteins appear when two amino acids link together through a peptide bond. They are involved in many chemical processes and attains elevated nutritional value.

In 1838 Jons Jacob introduced the term “Proteins,” derived from the Greek word “Proteios.” These are organ-specific from species to species. Approximately 20 different amino acids naturally occur in nature.

Proteins with the same function will have the same structure as well. The human body contains 10000 different kinds of proteins, and you can even find its sequence using Expasy Translate Tool.

A plant can synthesize amino acids, but animals cannot. You will comprehend the structure, properties, and sources of proteins after going through this article.

Peptide and Proteins

The compound formed by condensation of two or more similar or different amino acids is called peptides. They contain –CO-NH- bond in their structure.

It is called peptide bond or peptide linkage. The bond formed between the carbonyl group of one amino acid and an amino group of another amino acid with the elimination of a water molecule is called a peptide bond.

Two amino acids join to form three dipeptide units that further generate a tripeptide. A large number of amino acids join by peptide bonds and make a polypeptide. A polypeptide is a peptide with 10,000 molecular weight. Whereas a Peptide with a molecular mass of more than 10,000 is called protein. The human body contains at least 10,000 different proteins. They are present in the skin, hair, muscles, and non-bony tissues of the body. Let’s check out the structure and properties of polypeptides and proteins below.

Structure and Properties

According to Biochemistry Study, the amino acid composition of protein consists of a long chain of alpha-amino acids. α- amino acids define a unit having amino group (−NH2), carboxyl group, and an alkyl group

Acid nature of Amino Acid

In the acidic condition, pH is less than 4, and the –COO group combines with a hydrogen atom and converts it into –COOH group, which is uncharged.

Alkali Nature of Amino Acid

In alkali, condition pH remains above 9, the amino group (−NH+3) release hydrogen ion and convert it into (−NH2).

What is Zwitter Ion?

The molecule of amino acid consisting of dipolar ions is called a Zwitter ion. These amino acid carries both positive and negative charge and do not migrate with an electric field.

More than 100 amino acids are present, but almost 20 of them occur naturally.

Formation of Protein Molecules

Different alpha-amino acids link together through a peptide bond to form a long chain molecule called protein.

What is Peptide Bond?

A peptide bond is formed between the amino and carboxyl groups of two different amino acids through a peptide linkage. When this peptide molecule reacts with another amino acid to eliminate water, it yields a tripeptide.

peptide bond formation

We generally discuss the N- terminal or free alpha-amino acid on the left side and the C terminal or free carboxyl group found on the right side. These macromolecules are joined through a peptide bond. Many amino acids are linked and form the structure of the protein.

A long peptide chain involves the linkage of more than 100 amino acids.

Classification of proteins

classification of proteins

Proteins have three classes based on physicochemical properties 

  1. Simple Proteins
  2. Compound Proteins
  3. Derived Proteins

Simple Proteins

Proteins yield amino acids on hydrolysis, where their derivatives are called simple proteins. Examples include collagen, globulins, legumin, albumins, etc. Globulins are found in animals that are insoluble in water but soluble in a dilute salt solution. Similarly, body muscles contain lactoglobulins. The legumin and collagen are present in the connective tissues of the body. They are abundantly present, forming 25 to 35% of body protein.

Compound or Conjugate proteins

These molecules are attached with some non-protein groups called conjugated proteins, such as phospho-proteins conjugate with phosphoric acid and lipoproteins with lipids. (Cholesterol, Lecithin)

Derived Proteins

These are procured from simple and conjugated proteins that can be either primary or secondary derived proteins. Some examples include metaproteins and milk from the primary section, while proteoses, peptides, peptones, etc., are from the secondary.

Protein Sources

numerous protein sources

There are several protein sources, including meat, vegetables, poultry, eggs, seafood, soy products, seed, nuts, etc.

Alternative Sources

Numerous alternative sources like whey and soy hump are utilized for proteins. Its benefits mostly meet the person who exercises regularly because whey proteins are better for regenerating muscles & mass.

What is Whey Protein?

protien synthesis

Whey protein is a by-product of cheese making, basically, the watery portion that separates. This protein is usually utilized to improve athletic performances and strengthens the muscles. People with HIV defects consume whey protein that helps them reduce the weight loss problem. Moreover, it helps prevent allergic issues in infants.

Final Statement

We hope to clear all concepts relating structure and classification of proteins, but the knowledge doesn’t end here. Proteins are largely consumed in catalytic, nutritional, defensive, regulatory, and transport mechanisms.

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