VM

Lecture 6

Chemical Structure of Proteins

  • Proteins are essential for a healthy diet as they provide nitrogen necessary for amino acids.

    • Amino acids can be categorized as essential (must be consumed) and nonessential (can be synthesized by the body).

  • Proteins also contain sulfur.

Components of Amino Acids

  • Amino acids consist of an

    • Amine group (contains nitrogen)

    • Acid group

    • Side chain (varies between different amino acids)

  • Amino acids bond via peptide bonds.

    • Dipeptide (2 amino acids), Tripeptide (3), Oligopeptide (4-50), Polypeptide (50-99), Protein (100+).

Importance of Protein in Diet

  • Proteins are crucial due to their role in enzyme production; inadequate protein leads to health issues.

  • High protein diets are common in the U.S., often exceeding needs—advocating for more plant-based options.

  • Denaturation of proteins occurs through heat, acids, bases, salts, heavy metals, and agitation (e.g., cooking).

    • Denaturation can be beneficial (e.g., cooking eggs to prevent salmonella) but can cause issues if extreme (e.g., battery acid).

Amino Acid Sequences and Genetic Influence

  • DNA sequences determine the order of amino acids in proteins.

    • Alterations can lead to diseases (e.g., sickle cell disease—valine replaces glutamic acid).

  • Essential amino acids (9) vs. nonessential (11).

    • Complete proteins (contain all essential amino acids) mainly arise from animal products; some plant foods are complete (e.g., soy, quinoa).

Combining Proteins for Complete Intake

  • Incomplete proteins can be made complete through combinations (grains and legumes).

    • Examples include:

      • Peanut butter sandwich (grains + legumes)

      • Veggie stir fry (grains + vegetables)

      • Grains + seeds.

Protein Quality and Nutrition in Vegetarian Diets

  • Vegetarians may require higher protein intake due to reduced digestibility and fewer complete protein sources.

  • Understanding the combining of plant foods is essential for adequate amino acid intake.

  • Protein digestibility is measured with the PDCAAS (Protein Digestibility Corrected Amino Acid Score).

    • Highly digestible foods include tuna, chicken, and egg whites (100% score).

Daily Protein Requirements

  • DRI for healthy sedentary adults: 0.8 g/kg of body weight.

  • Athletes need significantly more (1.2 - 1.8 g/kg depending on activity level).

Protein Energy Malnutrition Diseases

  • Marasmus: Severe calorie and protein deficiency; leads to extreme weight loss and a lack of fatty insulation.

  • Kwashiorkor: Adequate calorie intake but insufficient protein; results in edema and fatty liver.

Overconsumption of Protein Risks

  • Excessive protein intake can lead to weight gain, heart disease, elevated homocysteine, kidney stress for individuals with existing conditions, kidney stones, osteoporosis, and potential cancer risk (linked to red meat).

  • High protein diets typically lack fiber, which is crucial for digestive health.

  • Higher water intake is necessary for protein metabolism (350g of water required for 100 calories of protein).

Summary of Protein Functionality

  • Proteins serve numerous functions:

    • Enzymes

    • Hormones (e.g., insulin, glucagon)

    • Structure (muscle tissue, connective tissue, skin)

    • Immune response (antibodies)

    • Fluid balance

    • Buffering maintenance of pH.

  • It's essential for an individual to maintain a balanced and adequate intake of protein for overall health.