2.16 Role of Proteins | Molecular Biology | Biology 11

Proteins are fundamental macromolecules involved in nearly all cellular functions. They are categorized based on their primary roles: structural (providing support and composition) and functional (participating in physiological activities).

Structural Proteins

These proteins are involved in the support, shape, and composition of body parts.

Protein	Role
Collagen	Forms the matrix of bone and cartilage; a key component of ligaments and tendons.
Elastin	Provides support and elasticity for connective tissues like tendons and ligaments.
Keratin	A fibrous protein that strengthens protective coverings such as hair, nails, quills, feathers, horns, and beaks.
Histone	A protein complex that helps organize and compact DNA into chromosomes within the nucleus.

Functional Proteins

These proteins are involved in various physiological and metabolic activities within the body.

Protein	Role
Enzymes	Act as biological catalysts to speed up biochemical reactions, thereby controlling the body's metabolism.
Hormones	Some hormones (e.g., insulin) are proteins that regulate physiological activities like blood glucose levels, digestion, and blood pressure.
Antibodies	Produced by white blood cells (WBCs) in response to foreign particles (antigens) to provide immunity.
Haemoglobin	A protein found in red blood cells (RBCs) responsible for transporting oxygen and, to a lesser extent, carbon dioxide.
Fibrinogen	A blood plasma protein that is converted to fibrin during the blood clotting process.
Ovalbumin & Casein	Storage proteins; Ovalbumin is found in egg whites and Casein is found in milk. They serve as a reserve of amino acids.

Movement and Transport

Proteins like Actin and Myosin are essential for muscle contraction and cellular movement. Additionally, proteins in the Plasma Membrane→ act as carriers or channels for Membrane Transport→.

Biochemical Tests for Proteins

Specific chemical tests can be used to confirm the presence of proteins or amino acids in a sample.

Test	Procedure	Positive Observation	Inference
Biuret Test	Add 2 ml NaOH and a few drops of 1% copper sulphate solution to 2 ml of the test solution. Shake well.	The solution turns pink or violet.	Protein is present.
Millon's Test	Add 1 ml of Millon's reagent to 1 ml of the test solution. Shake and let it settle. Heat if necessary.	An initial white precipitate forms, which turns red upon heating.	Protein is present.
Ninhydrin Test	Add 3-4 drops of aqueous ninhydrin reagent to 2 ml of the test solution. Boil the mixture and let it cool.	A purple or violet color appears.	Amino acids or protein is present.

Structural Proteins

These proteins are involved in the support, shape, and composition of body parts.

Protein	Role
Collagen	Forms the matrix of bone and cartilage; a key component of ligaments and tendons.
Elastin	Provides support and elasticity for connective tissues like tendons and ligaments.
Keratin	A fibrous protein that strengthens protective coverings such as hair, nails, quills, feathers, horns, and beaks.
Histone	A protein complex that helps organize and compact DNA into chromosomes within the nucleus.

Functional Proteins

These proteins are involved in various physiological and metabolic activities within the body.

Protein	Role
Enzymes	Act as biological catalysts to speed up biochemical reactions, thereby controlling the body's metabolism.
Hormones	Some hormones (e.g., insulin) are proteins that regulate physiological activities like blood glucose levels, digestion, and blood pressure.
Antibodies	Produced by white blood cells (WBCs) in response to foreign particles (antigens) to provide immunity.
Haemoglobin	A protein found in red blood cells (RBCs) responsible for transporting oxygen and, to a lesser extent, carbon dioxide.
Fibrinogen	A blood plasma protein that is converted to fibrin during the blood clotting process.
Ovalbumin & Casein	Storage proteins; Ovalbumin is found in egg whites and Casein is found in milk. They serve as a reserve of amino acids.

Proteins like Actin and Myosin are essential for muscle contraction and cellular movement. Additionally, proteins in the Plasma Membrane→ act as carriers or channels for Membrane Transport→.

Biochemical Tests for Proteins

Specific chemical tests can be used to confirm the presence of proteins or amino acids in a sample.

Test	Procedure	Positive Observation	Inference
Biuret Test	Add 2 ml NaOH and a few drops of 1% copper sulphate solution to 2 ml of the test solution. Shake well.	The solution turns pink or violet.	Protein is present.
Millon's Test	Add 1 ml of Millon's reagent to 1 ml of the test solution. Shake and let it settle. Heat if necessary.	An initial white precipitate forms, which turns red upon heating.	Protein is present.
Ninhydrin Test	Add 3-4 drops of aqueous ninhydrin reagent to 2 ml of the test solution. Boil the mixture and let it cool.	A purple or violet color appears.	Amino acids or protein is present.