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
A. Protein Functions
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.
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
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
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