Download Unit One: Introduction to Physiology: The Cell and General Physiology

Chapter 69: Protein Metabolism
Guyton and Hall, Textbook of Medical Physiology, 12th edition
Basic Properties
• Amino Acids- peptide linkages and peptide chains
Fig. 69.1 Amino acids
Protein Metabolism
• Other Linkages-hydrogen bonding
Protein Metabolism
• Transport and Storage of Amino Acids
a. Blood amino acids- account for only 2-3 mEq of
negative ions in the blood
b. When absorbed from the GI tract, most are
absorbed by the liver
c. Carried into cells by active transport; stored as
proteins once inside the cell
Protein Metabolism
• Functional Roles of Plasma Proteins
a. Major types are albumin, globulin, and fibrinogen
b. Albumin-provides colloid osmotic pressure
c. Globulins-enzymatic functions and immunity
d. Fibrinogen-converted into fibrin to form blood
clots
Protein Metabolism
• Formation of Plasma Proteins
a. All of the albumin, fibrinogen, and 50-80% of
the globulins are formed in the liver
b. Formation by the liver can be as much as 30 g/day
•
Plasma Proteins are a Source of Amino Acids for
Tissues
Protein Metabolism
Fig. 69.2 Reversible equilibrium among the tissue proteins, plasma proteins, and plasma amino acids
Protein Metabolism
• Essential and Nonessential Amino Acids
a. Group of amino acids that cannot be synthesized
by the body but must be supplied in the diet
b. Nonessential aa can be synthesized; mostly from
alpha-keto acids such as pyruvic acid (process of
transamination)
Protein Metabolism
• Essential and Nonessential Amino Acids
Fig. 69.3 Synthesis of alanine from pyruvic acid by transamination
Protein Metabolism
• Use of Proteins for Energy- once cells are filled to
their limit with proteins, any additional aa
are degraded and used for energy or stored as
fat or glycogen
a. Degradation occurs in the liver and begins with
the process of deamination
b. Begins with the removal of the amine group
Protein Metabolism
Transamnation schema for the deamination
of amino acids
Protein Metabolism
• Hormonal Regulation
a. Growth hormone increases the synthesis of cellular
proteins
b. Insulin is necessary for protein synthesis
c. Glucocorticoids increase the breakdown of most
tissue proteins
d. Testosterone increases protein deposition in tissues
e. Estrogen causes some deposition of protein in
tissues, but minor compared to testosterone
f. Thyroxine increases the rate of metabolism and
indirectly affects protein metabolism