Protein Structure Quiz

Primary Structure of Proteins

• The primary structure consists of a sequence of amino acids linked by peptide bonds.
• All bond angles in the structure are 120°, resulting in a zigzag arrangement in three-dimensional models.

Tertiary Structure

• Tertiary structure refers to the complete three-dimensional arrangement of atoms in a polypeptide chain.
• Myoglobin contains 153 amino acid residues, providing cardiac muscle with its red color.
• Hemoglobin is composed of four polypeptide chains (two α and two β subunits) carrying a heme unit.
• Both proteins are globular and conjugated, containing a heme, which surrounds a Fe²⁺ ion that binds to O₂.
• Hemoglobin transports O₂ in the bloodstream, while myoglobin stores O₂ in tissues.

Quaternary Structure

• The quaternary structure involves spatial relationships and interactions between multiple polypeptide chains.

classifications of Proteins Based on Function

• Catalytic Proteins - Enzymes that catalyze biochemical reactions.
• Defense Proteins - Immunoglobulins or antibodies that protect against diseases.
• Transport Proteins - Include hemoglobin (transports O₂), HDL, LDL.
• Messenger Proteins - Hormones such as insulin, glucagon, and human growth factor.
• Contractile Proteins - Myosin and actin involved in muscle movement.
• Structural Proteins - Collagen and α-keratin providing support and strength.
• Transmembrane Proteins - Include protein channels that facilitate transportation across membranes.
• Storage Proteins - Examples include ferritin and myoglobin which store nutrients.
• Regulatory Proteins - Bind with messenger molecules to regulate biological processes.
• Nutrient Proteins - Include casein in milk and ovalbumin in eggs.

Functions of Proteins

• Structure - Collagen and keratin are primary structural proteins found in skin, bone, hair, and nails.
• Catalysts - Enzymes catalyze virtually all biochemical reactions in living organisms.
• Movement - Myosin and actin are proteins that make up muscle fibers.
• Transport - Hemoglobin carries oxygen from lungs to cells; proteins also transport molecules across membranes.
• Hormones - Many hormones, including insulin and human growth hormone, are protein-based.
• Protection - Proteins like fibrinogen are involved in blood clotting; antibodies fight infections.
• Storage - Proteins such as casein and ovalbumin store nutrients for developing organisms; ferritin stores iron in the liver.
• Regulation - Certain proteins regulate gene expression and the timing of expression.

Characteristics of Amino Acids

• Amino acids link via amide bonds to form proteins.
• Functional groups include an amino group (NH₂) and a carboxyl group (COOH).
• Amino acids can be classified as:
  • Acidic Amino Acids - Contain an additional COOH group.
  • Basic Amino Acids - Contain an additional nitrogen atom (N).
  • Neutral Amino Acids - Lack acidic or basic properties.
• There are 20 naturally occurring amino acids, each represented by a common 3-letter or 1-letter abbreviation.

Classification of Proteins Based on Shape

• Fibrous Proteins - Have an elongated shape significantly longer in one dimension; typically insoluble and structural, providing support (e.g., collagen and keratin in connective tissues).