What Are Proteins? Lecture 9: Proteins. Proteins: large complex molecules composed of amino acids. Nutrition 150 Shallin Busch, Ph.D.

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1 What Are Proteins? Lecture 9: Proteins Nutrition 150 Shallin Busch, Ph.D. Proteins: large complex molecules composed of amino acids. Contain carbon, hydrogen, oxygen, nitrogen Primary source of nitrogen in our diets 20 different amino acids are used to make proteins The shape of a protein molecule is important for its function Amino Acid Structure Examples of Amino Acids Side group varies Amino group Acid group Glycine Alanine Aspartic acid Phenylalanine

2 Two Amino Acids can form a Dipeptide Amino acid + Amino acid Dipeptide Proteins fold to form complex structures Amino acid sequence determines the shape of the polypeptide chain Polypeptides are chains of 3+ amino acids. Digestion of Proteins Protein Digestion in Stomach Hydrochloric acid breaks down protein structure Hydrochloric acid activates pepsin Pepsin: an enzyme that breaks down proteins into short polypeptides and amino acids.

3 Pancreas Pancreatic enzymes called proteases complete the digestion of proteins into single amino acids Small intestine Specific carriers on intestinal cells transport amino acids, dipeptides, and tripeptides Enzymes in small intestine cells convert dipeptides and tripeptides to single amino acids If not used in intestinal cell, amino acids absorbed into the blood stream where they travel to liver Functions of Proteins in the Body Cell growth, repair, and maintenance Enzymes Hormones Fluid and electrolyte balance ph balance Antibodies to protect against disease Energy source Swelling due to edema caused by protein deficiency and resultant fluid imbalance. Adequate supplies of protein in the bloodstream keep fluids out of the tissues.

4 Enzymes: Facilitate both digestion (breakdown) and the formation of new complexes. A B Enzyme The separate compounds, A and B, are attracted to the enzyme s active site, making a reaction likely. A B Enzyme The enzyme forms a complex with A and B. A B New compound Enzyme The enzyme is unchanged, but A and B have formed a new compound, AB. How Much Protein Should We Eat? Recommended Dietary Allowance (RDA) 0.8 grams protein per kg body weight 12-20% of total energy intake should be from protein How Much Protein Should We Eat? Proper protein intake depends on Age Health status Activity level How Much Protein Should We Eat? People who require more protein include Children Adolescents Pregnant or lactating women Vegetarians

5 Body s Amino Acids Needs To build the body s many protein, all amino acids are needed. If the body lacks an amino acid, the protein will not be made. Essential amino acids Cannot be produced by our bodies Must be obtained from food Nonessential amino acids Can be made by our bodies Essential Amino Acids Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Non-essential Amino Acids Alanine Arginine Asparagine Aspartic Acid Cysteine Glutamic Acids Glutamine Glycine Proline Serine Tyrosine Proteins in the Diet Incomplete protein: does not contain all essential amino acids. Not sufficient for growth and health Considered a low quality protein Typically from vegetables (soy is exception) Complete protein: contains sufficient amounts of all 9 essential amino acids. Considered a high quality protein Typically from animal products Proteins in the Diet Mutual supplementation: using two incomplete proteins together to make a complete protein. Complementary proteins: two protein sources that together supply all 9 essential amino acids. Examples: beans and rice, hummus (garbanzo beans and sesame seeds), peanut butter and bread, tofu and broccoli with almonds, spinach salad with pine nuts and kidney beans

6 Complementary Proteins Isoleucine Lysine Methionine Tryptophan Legumes Grains Together Protein Quality (PDCAAS) Amino acid composition (Does it have amino acids in ratio that humans need?) Score dictated by limiting amino acid Digestibility Determined by studies in rats Table 6-3 Page 196 Risks of Too Much Protein? High cholesterol and heart disease Diets high in protein from animal sources are associated with high cholesterol Possible bone loss High protein diets MAY cause excess calcium excretion leading to bone loss Kidney disease High protein diets are associated with an increased risk of kidney disease Especially for people who may be susceptible to kidney disease

7 Protein Supplements? Inappropriate for MAJORITY of people Single and unusual combinations of amino acids can be harmful Toxicity Deficiency in other amino acids due to competition for absorption Can lead to diseases Ingestion of amino acids in foods is optimal for healthy individuals Vegetarian Diets Vegetarianism: restricting the diet to foods of plant origin and, in some cases, consuming some animal products There are many reasons to adopt a vegetarian diet both for health and ethics Health Benefits of Vegetarianism Lower intake of fat and total energy Lower blood pressure Reduce the risk of heart disease Reduce the risk of some types of cancer Fewer digestive problems Challenges of Vegetarianism Vegetarian diets can be low in some vitamins (B 12, Vitamin D) and minerals (iron, calcium, zinc). Vegetarians must plan a balanced and adequate diet (complementary proteins) Vegetarians can use soy products as a protein source (soy is a complete protein)

8 Protein Energy Malnutrition Disorder caused by inadequate intake of protein and energy. Marasmus Disease resulting from severely inadequate intakes of protein, energy, and other nutrients. Marasmus symptoms include There are two common forms: Marasmus Kwashiorkor Kwashiorkor Disease resulting from extremely low protein intake due to diet or infection Kwashiorkor symptoms include Some weight loss and muscle wasting Edema resulting in distention of the belly Retarded growth and development Severe wasting of muscle tissue Stunted physical growth Stunted brain development Anemia Child with kwashiorkor Belly is swollen due to: Edema Enlarged liver Potentially parasites