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Introduction, Classification, Chemical Nature and Biological Role of Proteins

Every cell contains protein, which is the most abundant macromolecule in life. Furthermore, it is the most versatile of all organic molecules.



Every cell contains protein, which is the most abundant macromolecule in life. Furthermore, it is the most versatile of all organic molecules in living systems and is found in countless varieties, ranging in size from very small peptides to very large polymers. Using peptide bonds, amino acids are assembled into polymers called proteins. Proteins are made up of twenty amino acids, which are naturally occurring. These amino acids combine to form proteins.


Physiochemically, structurally, shape-wise and solubility-wise, proteins can be classified into:
1. Simple proteins - An amino acid residue is all that a simple protein consists of. They can be hydrolyzed to yield constituent amino acids. The amino acids are further subdivided into:
  • Collagen, Elastin, and Keratin, which are fibrous proteins
  • Proteins found in the globules: Albumin, Globulin, Glutelin, Histones
2. Conjugated proteins - A conjugated protein is a protein that is attached to a non-protein moiety. Example – lipoproteins, metalloprotein, phosphoprotein, nucleoprotein
3. Derived protein - A derived protein is a degradation product or derivative of a simple or conjugated protein. They can be either two of the following type:
  • Primary derived protein – metaproteins, coagulated proteins, proteas.
  • Secondarily derived proteins – peptones, proteoses or albunoses, peptides.

Chemical nature

The unfolding of polypeptide chains can be caused by agents such as heat and urea that do not cause hydrolysis of peptide bonds. Secondary and tertiary structures are destroyed by denaturing agents, but the primary structure is left intact. The process of renaturing a denatured protein after removing the denaturing agent is known as renaturation.

A coagulum is an insoluble aggregate formed by protein denatured by heat. The majority of proteins, such as albumins and globulins, are not heated coagulable.

An amino acid's average molecular weight is 110. The molecular weight of a protein is determined by multiplying its amino acid content by 110. The molecular weights of proteins are different because of their amino acid compositions. Most proteins have a molecular weight of 5000 Daltons or more.

Biological role

Growing and repairing our bodies are facilitated by proteins, whose functions are endless. Furthermore, they are the most important final products of information pathways, as they have a wide range of biological functions.
  • An amino acid-containing protein plays numerous roles in the body (e.g., as an enzyme, a structural component, a hormone, and an antibody).
  • The structural components of hair, nails, and bones, for example, are keratin and collagen.
  • These proteins are the molecules that carry out genetic instructions.
  • Hemoglobin and special enzymes in red blood cells perform their functions in transporting oxygen and carbon dioxide.
  • They play a role in homeostatic control of circulating blood and interstitial fluid volume through their interaction with plasma proteins.
  • By producing thrombin, fibrinogen, and other proteins, they contribute to blood clotting.
  • Antibodies they produce protect against infections.
  • Nucleoproteins of the cell nucleus are responsible for hereditary transmission.
  • Storage proteins like ovalbumin and glutelin are among them.
  • As contractile proteins, actin and myosin play a crucial role in muscle contraction.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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