Chapter 6: Proteins

Overview of Protein Body is made up of thousands of protein substances Contains nitrogen Regulates and maintains body functions

Amino Acid R group Acid group Amine group NH2 O R C C OH H

Tyrosine Serine ProlineValine GlycineTryptophan GlutamineThreonine Glutamic acidPhenylalanine CysteineMethionine Aspartic AcidLysine AsparagineLeucine ArginineIsoleucine AlanineHistidine Nonessential AAEssential AA

Dietary Protein High-quality –complete Low-quality –incomplete All-or-none principle in protein synthesis Limiting amino acid Complementary protein

Limiting Amino Acid CCCCC AAAAAAAA CAR CAR CAR RRRRRR CAR CAR R A A A C is the limiting amino acid in this example

Complementary Protein Food 1 Food 2 CC CCCC AAAA AA CAR CAR CAR RRR RRR CAR CAR CAR

Complementary Protein Beans (legumes) GrainsNuts/seeds Vegetables

Protein Synthesis DNA contains coded instructions Copies of codes are transferred to the cytoplasm (via mRNA) Amino acids added one at a time with aid of tRNA

Protein Synthesis

Protein Turnover Protein undergo breakdown and synthesis Responds to change Amino acid can be recycled

Protein Organization Peptide bond Dipeptide Tripeptide Oligopeptide SH SH CH2 CH2 H O CH H2O H O CH H N C OH H N C OH H N C N C OH CH H O CH H O CH3 H2O CH3

Denaturation of Proteins Heat/acid/alkaline/enzymes Results in alteration of the protein’s three dimensional structure

Protein in Foods

Plant Protein Provide protein, minerals, and dietary fiber Contain no cholesterol Limited saturated fats Allow a few weeks for the GI tract to adjust to the higher fiber Availability of Beno®

Digestion of Protein in the Stomach Proteins are denatured by cooking and acid in the stomach Gastrin stimulates the release of acid and pepsin Pepsin is activated and breaks down proteins into peptones

Digestion of Protein in the Small Intestine Stimulates the release of CCK Pancreas release the protein splitting enzymes: trypsin, chymotrypsin, and carboxypeptidase into the duodenum The enzymes will break peptones into smaller peptides and amino acids Peptides and amino acids are ready for absorption

Protein Absorption Active absorption Whole proteins are broken down at the microvilli surface and within the absorptive cells Whole proteins are eventually broken down to amino acids Many different amino acid transport mechanisms Amino acids are sent to the liver via portal circulation

Functions of Proteins Building blocks of body components Maintain fluid balance Contribute to acid/base balance Building blocks for hormones and enzymes Immune function Gluconeogenesis Energy yielding

RDA for Protein Promotes equilibrium 0.8 gm of protein / kg of healthy body weight 154 lb. = 70 kg 2.2 kg/lb. 70 kg x 0.8 g protein = 56 g protein kg healthy body wt

RDA for Protein Increased by ~10-15 gm /day for pregnancy Endurance athletes may need gm/kg healthy weight About 8-10% of total kcals Most of us eat more than the RDA for protein Excess protein cannot be stored as protein New DRI for protein coming

Is a High-Protein Diet Harmful? Low in plant foods (fiber), vitamins, phytochemicals Intake of animal protein increases risk for heart disease (high in saturated fat) Excessive intake of red meat is linked with colon cancer Burden on the kidney Increase calcium loss National Academy of Sciences recommend no more than 2 x RDA for protein

Individual Amino Acid Supplement Supplement may cause imbalances and toxicities Body is designed to handle whole proteins Supplement can overwhelm the absorptive mechanism Excess of one AA can hamper absorption of other AAs

Malnutrition Protein-Energy Malnutrition Marasmus –Seen in hospitalized patients Kwashiorkor

Low protein density diet Energy needs are marginally met Signs and symptoms: –Apathy, listlessness, failure to grow, poor weight gain, change in hair color, nutrient deficiency, flaky skin, fatty infiltration in the liver, massive edema in the abdomen and legs

Marasmus Starving to death Insufficient protein, energy, nutrients “skin and bones” appearance Little or no subcutaneous fat Reduce brain growth

Soy Soy protein is similar to animal protein (used in school lunches) High in linoleic acid and some  linolenic acid Calcium source and bone health Isoflavones Heart disease Cancer

Vegetarian Diets Why become a vegetarian? Vegans Fruitarians Lactovegetarians Lactoovovegetarians

The Vegetarian Diet Pyramid