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Lesson 8 - Protein Functions and Metabolism

Student Performance Objectives

1. List 5 structural and 5 functional uses of proteins in the human body.
2. Define protein turnover, positive nitrogen balance and negative nitrogen balance.
3. Calculate the approximate daily protein requirement of a person of known sex and weight

Lesson Outline
A. Protein Functions
    1. Structure
        a. Bone substance - 1/3 collagen.
        b. Hair - keratin.
        c. Skin - collagen and elastin in the dermis; keratin in the epidermis.
        d. Cartilage - collagen and elastin in the matrix.
        e. Ligaments, tendons, and fascia - mostly collagen fibers.
        f. Muscle - actin and myosin myofilaments; troponin and tropomyosin regulators.
    2. Function
        a. Water balance - albumin of blood maintains intercellular fluid volume (in starvation, albumin drops
            and edema results).
        b. Acid-base balance - the proteins of the intra and extracellular fluids provide 75% of the buffering
            capacity of the human body. The protein buffer "buffers" the other buffers (e.g., bicarbonate,
        c. Immunity - some proteins act as surface markers on cells, antibodies are proteins of the
            gamma-globulin fraction of the blood, and the complement system.
        d. Metabolic regulators - as polypeptide hormones like oxytocin and as larger protein hormones like
            insulin and glucagon.
        e. Lipid transporters - as part of the blood's lipoprotein particles that transport triglycerides and
           cholesterol around the body (e.g., HDL and LDL particles).
        f. Mineral storage - as ferritin storing iron in bone marrow.
        g. Nervous system function - several amino acids serve as neurotransmitters.
        h. Blood clotting.
        i. Visual processing.
        j. Energy generation - oxidation of protein yields 4kcal/gram.
B. Protein metabolism
    1. Protein turnover - based on the action of cortisol.
        a. Obligatory conversion of approximately 35 grams of protein (from bone, immune system )into
           carbohydrate daily.
        b. Replaced by dietary intake of proteins digested to amino acids and then
            synthesized into replacement proteins.
    2. Nitrogen balance -
        a. Positive nitrogen balance - growth, pregnancy, body building.
        b. Negative nitrogen balance - dieting, fasting, and wasting illness.
    3. Individual, approximate daily, dietary protein need:
        Your weight in Kg x 0.8 = approximate grams protein required/day