Judith E. Brown Prof. Albia Dugger Miami-Dade College Proteins and Amino Acids Unit 15

Protein Protein is an essential component of all living matter, and is involved in almost every biological process in the body Protein Chemical substance in foods Made up of chains of amino acids

Protein’s Image Most people in the US get more than enough protein in their diets High protein diets are usually high in fat and low in fiber

Fat Content of “Lean” Meats

Functions of Protein Catabolism and Anabolism All proteins in the body are continually broken down and rebuilt

Hormones Hormones affect the body’s metabolic processes, such as glucose utilization and fat deposition Hormone A substance, usually a protein or steroid, produced by one tissue and conveyed by the bloodstream to another

Key Terms Immunoproteins Proteins that play a role in the functioning of the immune system (disease defense system) Example: antibodies Proteins found in blood that attack specific foreign proteins

Proteins as an Energy Source Protein can serve as an energy source 4 calories/gram Not a primary energy source Does not have a storage form in the body For proteins to be used as energy, nitrogen must be removed from amino acids Excess nitrogen is excreted in urine

Amino Acids Proteins are made of amino acids that have been linked by peptide bonds into chains 20 common amino acids Order of amino acids is determined by DNA Chains can have >2,500 amino acids Chains fold into complex shapes Order and shape determine protein function

Key Terms Essential (indispensable) amino acids Cannot be synthesized in adequate amounts by humans – must be obtained from the diet Nonessential (dispensable) amino acids Can be readily produced by humans from components of the diet

Complete Proteins Complete proteins Contain all of the essential amino acids in amounts needed to support growth and tissue maintenance Found in animal products such as meat, milk, and eggs

Incomplete Proteins Incomplete proteins Proteins that are deficient in one or more essential amino acids Proteins in plants are incomplete “Complementary” plants sources can be combined to form a “complete” source of protein

Complementary Plant Food Combinations

Amino Acid Supplements High intakes of individual amino acids can disrupt normal protein production Example: methionine Worsens symptoms of schizophrenia Promotes hardening of arteries Impairs fetal and infant development Causes nausea, vomiting

Supplements and Muscle Mass Athletes take amino acid supplements to increase muscle mass and strength The real key is resistance training followed by high-quality protein foods

Food as a Source of Protein In US, average protein intake exceeds RDAs 70% of protein comes from animal products Plant sources of protein are lower in fat Dried beans, grains Most food sources of protein also provide vitamins and minerals

Too Little Protein Protein deficiency can occur by itself, or with a deficiency of calories and nutrients Iron, zinc, vitamin B 12, niacin Body protein is used as an energy source during starvation Reduces strength, lowers immunity, causes abnormal organ functions and death

Too Much Protein Consumption of 45% of total calories from protein is considered too high Causes nausea, weakness, diarrhea High-protein diets Result in weak bones, kidney stones, cancer, heart disease, obesity Very high-protein diets Such as “rabbit fever,” may cause death