(39) Protein Part 1

Food Sources of Proteins

• Animal Sources

  • Commonly recognized sources: beef, pork, poultry, fish

  • Eggs: Rich in protein, primarily in egg whites

  • Dairy products: Milk, cheese, butter contain protein

• Plant Sources

  • Nuts and seeds: Significant protein content

  • Legumes and beans: Including chickpeas, peas, soybeans

  • Vegetables: Contain moderate amounts of protein (1-3 grams per serving)

    • Consuming recommended vegetable servings enhances protein intake

Nutritional Composition

• Animal Proteins

  • Do not contain carbohydrates, contain fats (higher levels of saturated fat)

  • Dairy products contain carbohydrates (lactose) and varying fats

    • Fat content depends on milk type (fat-free, 1%, 2%)

• Plant Proteins

  • Typically contain carbohydrates, varying protein, and fats

  • Essential: Proteins contain carbon, hydrogen, oxygen, and nitrogen

    • Difference from carbohydrates and lipids (which lack nitrogen)

Structure of Proteins

• Amino Acids

  • Basic structure: Carbon and hydrogen at the center, flanked by an amino group and a carboxyl acid group

  • Variable side groups define different amino acids

• Types of Amino Acids

  • 20 total, classified into:

    • Essential Amino Acids: Must be obtained from diet

    • Non-Essential Amino Acids: Synthesized in the body

    • Animal proteins generally complete in amino acids; plant proteins may lack lysine and methionine

    • Complete sources from plants: quinoa and soy; combining sources (e.g., rice and beans) achieves completeness

Protein Structure Complexity

• Levels of Structure

  • Primary Structure: Long chain of amino acids linked via peptide bonds

  • Secondary Structure: Electrical attractions create shapes

  • Tertiary Structure: Hydrophilic and hydrophobic interactions further define structure

  • Quaternary Structure: Multiple polypeptides combine for complexity

Digestion of Proteins

• Process Overview

  • Begins in the mouth (limited enzymatic activity)

  • Stomach: Pepsin enzyme and hydrochloric acid denature proteins, activating pepsinogen to pepsin

  • Small Intestine: Hydrolysis reactions break peptide bonds with the aid of various enzymes

    • Peptides must be broken down into amino acids for absorption

    • Complexity of digestion: Important to understand for digestive issues

Protein Synthesis

• Occurs after amino acids are absorbed into the bloodstream

• Importance of sufficient protein intake for metabolic functions:

  • Carbohydrates are preferred energy source, followed by fats

  • Protein Sparing: Bodily preference to use carbohydrates/fats over proteins for energy

Consequences of Inadequate Protein

• Deficiency: Insufficient dietary protein leads to health issues, especially in impoverished areas

• Excess Remnants: Excess amino acids lead to ammonia production, converted to urea for excretion in the kidneys

Functions of Proteins in the Body

• Structural materials: Skin, muscles, organs, bones

• Functions: Enzymes in metabolic reactions, hormones, fluid balance

• Transport: Proteins transport substances in the body

• Immune Function: Antibodies provide disease protection

• Energy: Minimal fuel source (around 10%); used when carbs and fats are unavailable

• Clotting and Collagen: Structural role in healing and blood clotting

• Importance of adequate dietary protein for optimal body function.