Module Six: Proteins

Module Six: Proteins

Introduction to Proteins

  • Welcome message and focus on proteins as one of the macronutrients.

  • Importance of discussing protein functions, dietary sources, and identification.

Learning Objectives

  • Discuss the identification of proteins.

  • Explore Dietary Reference Intakes (DRIs) for proteins.

  • Review health benefits related to protein.

Overview of Proteins in the Body

  • Proteins constitute approximately 20% of the human body.

  • Functions served by proteins include:

    • Structural integrity

    • Immune function

    • Muscle maintenance

  • Unique characteristics of proteins compared to other macronutrients:

    • Proteins contain nitrogen, which is absent in carbohydrates and lipids.

Energy Contribution from Proteins

  • Protein provides energy but is not the primary source:

    • Main energy sources are carbohydrates and lipids.

    • Proteins are not stored in the body; excess protein cannot be stored like fats and carbohydrates.

Composition of Proteins

  • Proteins are composed of amino acids, known as the building blocks of proteins.

  • Over 20 different amino acids exist, each with distinct functions.

    • Combinations of amino acids create various proteins.

Structure of Amino Acids

  • Amino Acid Structure:

    • Central carbon atom connected to four groups:

    1. Amino group (amine)

    2. Hydrogen group

    3. Carboxylic acid group

    4. R-group (side chain, varies among amino acids)

  • Examples of amino acids:

    • Glycine (simplest structure)

    • Complexity varies with amino acids being nonpolar, charged, acidic, or basic types.

Types of Amino Acids

  • Essential Amino Acids (9 total):

    • Required from dietary intake; our bodies cannot synthesize them.

  • Non-Essential Amino Acids (11 total):

    • Synthesized in adequate amounts by the body through transamination (transfer of an amine group).

  • Conditionally Essential Amino Acids:

    • Not normally essential but must be consumed during certain conditions (e.g., infancy, growth, illness).

Peptide Bonds and Protein Structure

  • Amino acids linked together by peptide bonds, forming proteins.

  • Four levels of protein structure:

    1. Primary Structure: Linear sequence of amino acids.

    2. Secondary Structure: Local folding (e.g., alpha helices, beta sheets).

    3. Tertiary Structure: Overall 3D shape of a polypeptide.

    4. Quaternary Structure: Arrangement of multiple polypeptide chains (e.g., hemoglobin).

Protein Denaturation

  • Definition: Alteration of a protein's physical properties due to changes in structure.

  • Causes of denaturation include:

    • Heavy metals, heat, acids, enzymes, agitation, and alcohol.

  • Examples of denaturation in cooking:

    • Cooking eggs causes proteins to unfold, resulting in texture changes (e.g., whipped egg whites into meringue).

Protein Functionality and Shape

  • Protein function is determined by shape; structure arises from amino acid sequencing.

  • Accurate amino acid sequences lead to predictable protein structures; errors can cause diseases (e.g., sickle cell anemia).

Functions of Proteins in the Body

  1. Hormonal Functions:

    • Regulate physiological processes (e.g., insulin and glucagon for glucose homeostasis).

  2. Structural Functions:

    • Proteins provide structure to cells and tissues (e.g., collagen).

  3. Fluid Balance:

    • Proteins such as albumin help maintain osmotic balance, crucial for proper fluid distribution in the body.

    • Edema arises from disrupted balance due to low protein levels.

  4. pH Balance:

    • Proteins serve as buffers to maintain blood pH (normal range: 7.35 - 7.45).

  5. Immune Function:

    • Proteins defend against foreign pathogens (e.g., antibodies).

  6. Enzymatic Functions:

    • Enzymes speed up biochemical reactions needed for digestion and metabolism (e.g., salivary amylase, lipase).

    • Deficiencies can lead to metabolic disorders (e.g., phenylketonuria - PKU).

  7. Transport Functions:

    • Proteins facilitate transportation of molecules in circulation (e.g., hemoglobin for oxygen transport).

    • Proteins interact with lipids for nutrient distribution (e.g., lipoproteins).

  8. Energy Source:

    • Proteins can be used for energy but are less efficient than carbohydrates or fats.

Protein Turnover and Nitrogen Balance

  • Definition: Continuous synthesis and breakdown of proteins in the body.

  • New protein synthesis requires essential amino acids; absence leads to limiting amino acids.

  • Amino acid pool available through protein breakdown.

  • Deamination Process:

    • Amine group removal from amino acids, producing ammonia that gets converted to urea for excretion.

  • Nitrogen Balance Concept:

    • Evaluates nitrogen consumed versus nitrogen excreted to determine protein needs.

Dietary Reference Intakes (DRIs) for Protein

  • Focuses on maintaining a balance of protein intake and utilization.