Proteins classification based on composition

Proteins can be classified based on their composition into three main types:

 

1. Simple proteins (Homoproteins)- Composed only of amino acids.

Examples:

• Albumins (e.g., Serum albumin)

• Globulins (e.g., Immunoglobulins)

• Histones (e.g., Nucleoproteins)

• Protamines (e.g., Salmine in fish sperm)

 

2. Conjugated proteins (Heteroproteins)- Contain both amino acids and a non-protein component (prosthetic group).

 

Subtypes based on the prosthetic group:

• Glycoproteins – Carbohydrate (e.g., Mucin)

• Lipoproteins – Lipid (e.g., HDL, LDL)

• Metalloproteins – Metal ions (e.g., Hemoglobin with iron)

• Phosphoproteins – Phosphate group (e.g., Casein in milk)

• Nucleoproteins – Nucleic acid (e.g., Ribosomes)

• Chromoproteins – Colored prosthetic group (e.g., Hemoglobin, Cytochromes)

 

3. Derived proteins- Formed by the partial hydrolysis or degradation of simple or conjugated proteins.

 

Examples:

• Peptones – Intermediate products of protein digestion

• Proteoses – Smaller fragments of proteins

• Polypeptides – Short chains of amino acids

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