Proteins Quiz

Proteins

• Complex organic macromolecules containing carbon, hydrogen, oxygen, nitrogen, and usually sulfur
• Linear polymers of amino acids connected by peptide bonds
• Diverse and abundant class of biomolecules, making up about 50% of the dry weight of cells
• Not stored in the body, so they must be consumed daily

Amino Acids

• Organic compounds containing an amino group (NH2) and a carboxylic acid group (COOH)
• Building blocks of proteins
• 20 common amino acids, with most being chiral molecules
• Most amino acids are α-amino acids, and all amino acids in the body are L-isomers
• Exceptions: Glycine (simplest amino acid, achiral) and Proline (imino acid)

Classification of Proteins

• According to composition: derived proteins (e.g. denatured proteins and peptides)
• According to nutritional basis:
  • Complete proteins: contain all essential amino acids in correct proportion (e.g. meat, fish, dairy, egg)
  • Incomplete proteins: lack one or more essential amino acids in correct proportion (e.g. grains, nuts, beans, seeds, peas, corn)
  • Complementary proteins: combining two or more incomplete proteins to create a complete protein

Properties of Proteins

• Denaturation: loss of secondary, tertiary, and quaternary structures, but primary structure remains intact
• Factors that cause protein denaturation: heat, detergents, acids and bases, salts, reducing agents, heavy metal ions, alcohol, and mechanical stress

Protein Hydrolysis

• Breaking peptide bonds by treatment with aqueous acid, base, or certain enzymes
• Primary structure of protein is cleaved by the addition of water
• Involved in the development of antibodies and has important antiviral properties

Specific Amino Acids

• Leucine: helps maintain nitrogen balance and energy supply, supports muscle building, and lowers cholesterol and LDL levels
• Limiting amino acids: amino acids in shortest supply in relation to need, inhibits protein synthesis, and usually found in incomplete proteins

Examples of Limiting Amino Acids

• Lysine: involved in growth, tissue repair, and collagen synthesis
• Threonine: involved in lipid metabolism and intestinal health
• Methionine: involved in detoxification, antioxidant functions, and liver health
• Tryptophan: involved in neuronal function, immunity, and gut homeostasis

Functions of Proteins

• Structure: provides strength to cells and tissue, chief constituents of skin, bones, hair, and nails
• Other functions: enzymatic, transport, storage, and defense-related functions