Proteins and Amino Acids: Function Follows Form

1. Proteins and Amino Acids:Function Follows Form BIOL 103, Chapter 7

2. Today’s Topics • Why is Protein Important? • Amino Acids are building blocks of proteins • Functions of Body Proteins • Protein Digestion and Absorption • Proteins in the Body • Proteins in the Diet • The Pros and Cons of Vegetarian Eating • The Health Effects of Eating Too Little or Too Much Protein

3. Why is Protein Important? • A part of every cell • Needed in thousands of chemical reactions • Keep us “together” structurally • In short, proteins have many, many functions from replacing skin cells, producing antibodies to assisting in nutrient transport and muscle contractions.

4. Food Sources of Proteins • Beef • Chicken • Fish • Milk • Plant foods: beans, peas, grains, nuts, seeds, and vegetables (garlic, green peas, mushrooms)

5. Amino Acids are Building Blocks of Proteins • Proteins are sequences of amino acids • There are 20 amino acids: • Essential (9) • Non-essential (11) • Conditionally essential (6) • Table 7.1 List of Amino Acids

6. Amino Acids Identified by Side Chains

7. Protein structure: unique 3D shapes and functions • Amino Acid Sequence • Amino acids are linked by peptide bond: • Dipeptide: 2 amino acids • Oligopeptide: 4-10 amino acids • Polypeptide: >10 amino acids • Protein: a chain with >50 amino acids • Protein shape • A sequence of AA determines protein shape • Shape of protein determines its function.

8. Protein Denaturalization: Destabilizing a Protein’s Shape • There are factors that can cause a protein to unfold and lose shape (denature) • Changes in Acidic or Alkalinity in environment • High temperature/heat • Alcohol • Oxidation • Denatured proteins lose their ability to function properly.

9. Functions of Body Proteins

10. Protein Digestion • Protein digestion • Cells produce proteases (protein-digesting enzymes)as proenzymes (inactive forms of enzymes) • In the stomach: • Proteins are denatured by HCl • Pepsin begins digestion: 10-20% of proteins • Which one is a protease? A proenzyme?

11. Protein Digestion and Absorption • In the small intestine: • Proteases (from pancreas) break down remaining proteins  small peptides • Intestinal lining cells break down small peptides  amino acids • Amino acids are then absorbed into your intestinal cells  travel via portal vein to liver  released to general circulation

12. Summary of Protein Digestion and Absorption

13. Undigested Proteins • If not digested, continues down the GI tract  feces • Diseases of the intestinal tract cause problems with digestion/absorption of proteins • Celiac disease: allergic to protein gluten • Cystic fibrosis: sticky mucus prevents digestive enzymes (e.g. proteases) from reaching small intestine  poor digestion  nutrients are not absorbed  malnutrition

14. Proteins in the Body • Protein Synthesis: • Draws on AA pool as needed. If your body is missing… • Non-essential AA: • Cell will make that AA • Obtain it from liver • Essential AA: • Body make break down its own protein to supply the AA

15. Proteins in the Body • Amino Acid Pool and Protein Turnover • Cells in your body constantly build and breakdown proteins  Protein turnover • “protein recycling” • When cells make proteins, they use amino acids from amino acid pool: available amino acids in body tissues and fluids that can be used to make new proteins.

16. Proteins in the Body • Synthesis of non-protein molecules • Proteins are precursors of DNA, RNA, and neurotransmitters • Protein and Nitrogen Excretion • Breakdown of amino acids by removing nitrogen (amino) group/-NH2 • Amino groups converted to urea • Urea + water = urine excretion (in kidney)

17. Function of Blood Amino Acid Pool

18. Nitrogen Balance • We can evaluate our nitrogen balance to evaluate what is happening in our body • Nitrogen intake vs. nitrogen output • Nitrogen equilibrium • Nitrogen intake = nitrogen output • Healthy adults • Positive nitrogen balance • Nitrogen intake > Nitrogen output • Growth; recovery from illness • Negative nitrogen balance • Nitrogen intake < Nitrogen output • Injury and illness

19. Proteins in the Diet • Recommended protein intake • Adult RDA = 0.8g/kg of body weight • Infants have highest needs relative to body weight • Why? • Physical stress increase your body’s needs for proteins • Infection, burns, fevers, surgery, intensive weight training • Consumption in the US • Generally within or higher than recommended range

20. Problem Set 7, Question 1: • How is it that our bodies are able to synthesize so many proteins in our body when our dietary protein requirement is relatively low?

21. Protein Quality • Protein Quality • Complete proteins: supply all essential amino acids • “high-quality proteins” • Examples: animal proteins, soy proteins • Incomplete proteins: low in one or more essential amino acids • “low quality proteins” • Examples: most plant proteins

22. Protein Quality • Incomplete and Complementary Proteins • Except soy, proteins in other plant foods is incomplete (lacks 1 or more essential AA). • Two incomplete complementary proteins = complete protein • Examples: rice and beans, peanut butter and bread, pea soup with crackers, corn and tortilla.

23. Evaluating Protein Quality • A high-quality protein: • Provides all the essential amino acids at amounts the body needs • Provides enough other amino acids to serve as nitrogen sources for making non-essential amino acids • Easy to digest • Protein digestibility-corrected amino acid score (PDCAAS): measure of protein quality that takes account the AA composition of the food and the digestibility of the protein.

24. Proteins and Amino Acids as Additives and Supplements • Protein and AA additives • Contribute to structure, texture, taste of foods • Protein and AA supplements • Used for a variety of reasons: dieters, athletes, certain diseases. • Risks are unknown

25. Vegetarian vs. Vegan Vegetarian Vegan “Diet + Lifestyle” Don’t Eat: Meat, eggs, milk, honey, or any food derived from animals. Products: Avoids using animal-derived products including clothing, cosmetics, household, foods. • “Diet” • Don’t Eat: Meat, seafood • Types: • Ovo-vegetarian: eats eggs • Lacto-vegetarian: eats dairy products • Products: Don’t mind using animal-derived products.

26. Pros and Cons of Vegetarian EatingProblem Set 7, Question 4 Health Benefits Health Risks

27. The Pros and Cons of Vegetarian Eating • Diet recommendations (pg. 258): • Choose a variety of foods • Choose whole, unrefined foods • Choose a variety of fruits and vegetables • Choose lower-fat dairy products and eggs in moderation • Consume a regular source of vitamins B12 and D • Fortified foods or supplements

28. The Health Effects of Too Little Protein • Dietary protein = essential amino acids • Protein deficiency: occurs when energy and/or protein intake is inadequate • Protein-energy malnutrition (PEM) • Kwashiorkor: severe protein deficiency • Symptoms: edema, poor growth, bloated belly • Affects those between age of 18-24 months old • Associated with extreme poverty

29. The Health Effects of Too Little Protein • PEM, cont. • Marasmus: severe calorie deficiency • Chronic PEM; “withering” • Affects Infants and 6-18 months old children • Usually the children are short and thin for their age • How to treat? • Nutritional rehabilitation • Gradual and careful refeeding • Must start with fluid and electrolyte balance, then introduce nutrients

30. Protein-Energy Malnutrition

31. The Health Effects of Too Much Protein

32. Problem Set 7, Q5 • Name two health effects related to consuming a very high protein diet.