Week Six: Protein

Week Six: Protein

Introduction to Proteins

  • Proteins are essential macromolecules composed of:

    • Carbon

    • Hydrogen

    • Oxygen

    • Nitrogen (distinguishing feature from lipids and carbohydrates)

  • Unique roles in the body due to nitrogen content.

Structure of Proteins

  • Composed of:

    • An amine group (contains nitrogen)

    • Unique amino acid side chains

  • Amino Acids:

    • Difference in composition of side chains differentiates proteins.

    • Categories:

    • Indispensable Amino Acids:

      • Cannot be synthesized by the body; must be obtained from food.

    • Conditionally Indispensable Amino Acids:

      • Essential under certain circumstances.

    • Dispensable Amino Acids:

      • Can be synthesized by the body.

Recycling of Amino Acids

  • Unneeded proteins are dismantled into single amino acids.

  • The body recycles amino acids to preserve nitrogen.

  • Amino acids are used as:

    • Raw materials for building proteins.

    • Emergency energy production when carbohydrates are insufficient.

Examples of Proteins and Their Functions

  • Insulin:

    • Acts as a hormone regulating blood glucose levels.

    • Composed of 51 amino acids.

  • Collagen:

    • Structural protein in bones and teeth.

    • Composed of 19 amino acids.

  • Hemoglobin:

    • Oxygen transport protein.

    • Composed of 574 amino acids.

Genetic Determinants of Protein Structure

  • Each protein's composition and shape is genetically determined.

  • Genetic sequence alterations can lead to diseases, e.g., sickle cell disease.

Denaturation of Proteins

  • Denaturing Agents:

    • Heat, alcohol, acids, bases, salts of heavy metals.

  • Denaturation changes protein structure and functionality.

  • Example: Frying an egg denatures proteins, altering their structure irreversibly.

Protein Digestion Process

  1. Mechanical Digestion: Begins in the mouth with chewing.

  2. Chemical Digestion in the Stomach:

    • Hydrochloric acid denatures proteins.

    • Enzyme pepsin breaks down bonds between amino acids.

  3. Small Intestine Digestion:

    • Proteins are further broken down into polypeptides, dipeptides, and tripeptides.

      • Polypeptide: 10 or fewer amino acids.

      • Dipeptide: 2 amino acids.

      • Tripeptide: 3 amino acids.

    • Most dipeptides and tripeptides are reduced to single amino acids for absorption.

    • Absorption sites for different amino acids in intestinal cells.

    • Amino acids released into bloodstream and transported to the liver.

Functions of Proteins in the Body

  1. Support Growth and Maintenance:

    • Amino acids are continuously needed for:

      • Protein turnover: replacement of old proteins.

      • Growth and tissue repair.

    • In adults, approximately 300-400 grams of protein turns over each day, accounting for 20% of basic energy needs.

  2. Building Enzymes, Hormones, and Other Compounds:

    • Enzymes: Catalysts for chemical reactions; a single enzyme can facilitate several hundred reactions per second.

    • Hormones: Messenger molecules regulating functions like metabolism and blood glucose levels.

    • Other Compounds: Synthesis of neurotransmitters from tyrosine and other compounds.

  3. Immune System Functionality:

    • Creation of antibodies to fight foreign substances (antigens).

    • Each antibody targets a specific antigen, aiding in the development of immunity.

    • Antibodies are large proteins released into the bloodstream in response to antigens (bacteria, viruses, toxins).

  4. Fluid and Electrolyte Balance:

    • Proteins regulate internal fluid quantities in cells and bloodstream.

    • Transport proteins facilitate movement of substances in and out of cells.

  5. Acid-Base Balance Maintenance:

    • Proteins act as buffers in the blood, managing hydrogen concentrations.

    • Imbalances can lead to acidosis (excess acid) or alkalosis (excess base), which can be life-threatening.

  6. Blood Clotting and Wound Healing:

    • Special blood proteins initiate clotting in response to injury, preventing blood loss.

  7. Energy Production:

    • When needed, proteins can be dismantled to provide energy or stored as fat.

    • Excess amino acids may be excreted or converted to glucose or fat.

Amino Acid Supplements

  • Regulated as natural health products in Canada.

  • Health claims about amino acid supplements should be critically assessed due to limited safety evidence.

  • Known side effects include:

    • Digestive disturbances.

    • Excess water in the digestive tract.

    • Increased requirement for thiamine.