Proteins Structure and Composition

Protein Structure

• Proteins are macromolecules composed of long chains of amino acids linked by peptide bonds.
• Polypeptides contain additional intermolecular forces, contributing to their structure.
• A protein may consist of one or more polypeptide chains.

Examples of Proteins

• Albumin: Comprises a single polypeptide chain of 585 amino acid residues.
• Insulin: Consists of two polypeptide chains.
• Collagen: Made up of three intertwined polypeptide chains.
• Hemoglobin: Contains four polypeptide chains.

Classification Based on Function

• Catalytic Proteins: Enzymes that catalyze biochemical reactions.
• Structural Proteins: Provide structural support; examples include collagen and elastin.
• Contractile Proteins: Involved in muscle contraction; actin and myosin are key examples.
• Transport Proteins: Carry substances throughout the body; hemoglobin and albumin are notable examples.
• Regulatory Proteins: Regulate metabolism; includes hormones like ACTH and insulin.
• Genetic Proteins: Associated with genetic material; histones exemplify this category.
• Protective Proteins: Function in defense; immunoglobulins serve this purpose.

Classification Based on Composition

• Simple Proteins: Composed solely of amino acids.
• Conjugated Proteins: Contain both protein and non-protein components (prosthetic groups).
• Derived Proteins: Result from the degradation of native proteins.

Classification Based on Composition and Solubility

• Simple Proteins Examples: Albumins and globulins.
• Conjugated Proteins Examples: Include glycoproteins and lipoproteins.
• Derived Proteins: Created from hydrolysis of proteins into peptones, peptides, and amino acids.

Classification Based on Shape

• Globular Proteins: Spherical or oval structures; examples include albumin and globulins.
• Fibrous Proteins: Elongated or needle-like structures; examples include collagen and elastin.

Classification Based on Nutritional Value

• Nutritionally Rich Proteins: Contain all essential amino acids; casein in milk is a prime example.
• Incomplete Proteins: Lack at least one essential amino acid; many plant proteins from pulses are deficient in methionine.
• Poor Proteins: Missing more than one essential amino acid; zein from corn lacks tryptophan and lysine.

Learn about proteins, macromolecules made up of amino acids linked by peptide linkages and intermolecular forces. Understand how polypeptides form proteins, with examples of albumin, insulin, and collagen.