Proteins: Classification and Types

Proteins: Classification and Types

• Proteins are classified based on their chemical composition and properties into three main groups: Simple proteins, Conjugated proteins, and Derived proteins.
• Simple proteins yield only amino acids or their derivatives upon hydrolysis.
• Albumins are a type of simple protein with the following characteristics:
  • They have a low molecular weight (around 68,000).
  • They are soluble in pure water.
  • They are heat-coagulable.
  • Found mainly in animal tissues.
• Globulins are another type of simple protein with the following characteristics:
  • They have a higher molecular weight (approximately 150,000).
  • They are insoluble in pure water but soluble in diluted solutions of salts, alkalis, and acids.
  • They are heat-coagulable.
  • Found in both animal and plant tissues.
• Glutelins are plant proteins that are insoluble in neutral solvents but soluble in very dilute acids and alkalis.
• Prolamins (or alcohol-soluble proteins) are found in plant seeds and are soluble in 70-80% alcohol but insoluble in water, neutral solvents, or absolute alcohol.
• Histones are basic proteins that are positively charged and bind to negatively charged nucleic acids.
• Protamins are also basic proteins and are rich in arginine. They often occur in tissues in combination with nucleic acids.
• Albuminoids (or scleroproteins) are a group of highly insoluble proteins that make up structural components of the body. Examples include keratin, collagen, and elastin.
  • Keratin is found in hair, fingernails, and skin and is rich in cysteine residues, forming cysteine cross-links.
  • Collagen is the most abundant protein in vertebrates and is a major component of bone, skin, tendons, and cartilage.

Collagen: Structure and Function

• Collagen is a fibrous protein that provides structural support to tissues.
• The basic unit of collagen is the tropocollagen molecule, which is a triple helix composed of three polypeptide chains.
• Each chain has about 1000 amino acids and is characterized by a repeating tripeptide sequence: Gly-X-Y.
  • X is often proline.
  • Y is usually proline or hydroxyproline.

This quiz explores the classification of proteins, focusing on simple, conjugated, and derived proteins. It highlights specific types such as albumins, globulins, and glutelins, along with their characteristics and solubility properties. Test your knowledge on the different classes and properties of proteins.