SAS 13

• Proteins are polypeptide structures made of amino acid residues, carrying out various organism functions
• Primary Structure of a protein is a linear chain of amino acids
• Secondary Structure of a protein consists of regions of amino acid chains stabilized by hydrogen bonds, forming alpha-helix and beta-pleated sheets
• Tertiary Structure of a protein is the three-dimensional shape determined by interactions of side chains
• Quaternary Structure is formed by interactions between two or more polypeptides, influencing the protein's shape
• Simple Proteins:

  • Yield only amino acids upon hydrolysis
  • Classified based on solubility in solvents and heat coagulability
• Albumins:

  • Proteins soluble in water, dilute acids, and alkalies
  • Coagulated by heat
  • Deficient in glycine
  • Examples: Serum albumin and Ovalbumin
• Globulins:

  • Proteins insoluble in water but soluble with neutral salts
  • Coagulated by heat
  • Deficient in methionine
  • Examples: Serum globulin and Fibrinogen
• Prolamins:

  • Proteins insoluble in water but soluble in aqueous alcohol
  • Yield proline and amide nitrogen upon hydrolysis
  • Deficient in lysine
  • Examples: Gliadin and Zein
• Glutelins:

  • Proteins insoluble in water and alcohol but soluble in alkalies and acids
  • Found in plants
  • Example: Glutenin
• Histones:

  • Small basic proteins with large amounts of histidine
  • Soluble in water but insoluble in ammonium hydroxide
  • Occur in globin and nucleoproteins
• Protamines:

  • Simple proteins soluble in water
  • Not coagulated by heat
  • Basic due to arginine
  • Found in sperm cells of certain fish
  • Lacking tyrosine and tryptophan
• Albuminoids:

  • Highly stable and insoluble proteins
  • Similar to albumin and globulins
  • Resistant to enzymes
  • Form supporting structures like hair, horn, and nails
• Conjugated Proteins are simple proteins combined with non-protein substances known as prosthetic groups
• Nucleoproteins are basic proteins in salt combination with nucleic acids as the prosthetic group, important in nuclei and chromatin
• Mucoproteins are proteins composed of simple proteins with carbohydrates like mucopolysaccharides, e.g., hyaluronic acid and chondroitin sulphates
• Chromoproteins are proteins containing colored prosthetic groups, e.g., haemoglobin, flavoprotein, and cytochrome
• Lipoproteins are proteins conjugated with lipids such as neutral fat, phospholipids, and cholesterol
• Metalloproteins are metal-binding proteins like transferrin combining with iron, copper, and zinc
• Phosphoproteins are proteins containing phosphoric acid linked to certain amino acids like serine, e.g., casein in milk
• Derived Proteins are obtained through partial to complete hydrolysis from simple or conjugated proteins by acids, alkalies, or enzymes
• Primary-derived Proteins are protein derivatives formed with minimal changes in the protein molecule and properties, with little hydrolytic cleavage of peptide bonds
• Metaproteins are proteins formed by the action of acids and alkalies on proteins, insoluble in neutral solvents
• Coagulated Proteins are insoluble products formed by heat or alcohol action on natural proteins, like cooked meat and cooked albumin
• 1. Proteans: Insoluble products formed by water, dilute acids, and enzymes, particularly from globulins but insoluble in dilute salt solutions.
• Secondary-derived Proteins are formed through the progressive hydrolytic cleavage of peptide bonds in a protein molecule
• Proteoses are hydrolytic products of proteins soluble in water and not coagulated by heat
• Peptones are hydrolytic products simpler in structure than proteoses, soluble in water, and not coagulated by heat
• Peptides are composed of relatively few amino acids, water-soluble, and not coagulated by heat
• In the complete hydrolytic decomposition process, the order is: protein, protean, metaprotein, proteoses, peptones, peptides, and finally amino acids
• Catalytic Proteins, known as enzymes, function as biocatalysts within living cells, significantly enhancing reaction rates
• Regulatory Proteins are polypeptides and small proteins with crucial regulatory roles in complex metabolic reactions, such as growth hormone and insulin
• Protective Proteins, like antibodies, defend against diseases by binding to foreign substances and antigens
• Storage Proteins store amino acids as nutrients and building blocks, like globulins in pulses and glutelins in rice
• Transport Proteins bind and transport specific molecules through blood, like haemoglobin transporting oxygen
• Toxic Proteins, like ricin in castor beans or trypsin inhibitors, have toxic properties that prevent protein availability
• Structural Proteins serve as structural materials, like myosin in muscles, keratin in skin and hair, and collagen in connective tissue
• Contractile Proteins, like actin and myosin, are essential for the contractile system in skeletal muscle
• Secretary Proteins, like fibroin secreted by spiders and silkworms, are used to form webs and cocoons
• Exotic Proteins, like antifreeze glycoproteins in Antarctic fishes, prevent freezing in extremely cold waters