2CHAPTER 6: PROTEINS & AMINO ACIDS LEARNING OBJECTIVESAt the end of this chapter, you should be able to:Describe the structure of proteins and amino acids and explain their role in health and diseasePlan a diet to meet protein recommendations
3THINK about this – then share within a PAIR – then SHARE with the class What do you know about proteins and amino acids?What are benefits of eating plant foods over animal foods?
4Sources of protein Animal: meat, eggs, dairy products High in saturated fat and cholesterol; provide B vitamins and some absorbable mineralsPlant: grains, nuts, legumesLow in saturated fat and cholesterol; high in fiber, phytochemicals, and unsaturated fatLegumes: starchy plant seeds producing bean pods, including peas, peanuts, beans, soybeans, lentils
5Sources of proteina. Animal products are high in protein, iron, zinc, and calcium but add saturated fat and cholesterol to the diet.
6Sources of proteinMichael Newman/Photo Editb. Plant sources of protein are rich in fibre, phytochemicals, and monounsaturated and polyunsaturated fats.
7Amino acids Amino acids: building blocks of proteins Carbon, hydrogen, amino group (contains nitrogen), acid group, and a unique side chain20 different side chains make 20 different amino acids
8Amino acids link to form proteins We obtain amino acids from eating plant and animal foods.Our bodies reassemble the amino acid building blocks into our body proteins.
9Match the building blocks with the nutrient: ____ complex carbohydrates a) amino acids____ triglycerides b) fatty acids and glycerol____ proteins c) monosaccharides
10Essential vs. non-essential amino acids Essential/indispensable: Cannot be made in the body so “essential” to eat themIf one is missing, body proteins are broken down to make new proteinsNon-essential/dispensable: Body can make them from essential amino acids so not essential to eat them
11Essential vs. non-essential amino acids b. Twenty amino acids arecommonly found in proteins. The table shown here lists them based on whether they are essential or nonessential and indicates those that are conditionally essential.
12Essential vs. non-essential amino acids Food AFood B
13Essential vs. non-essential amino acids Can you use only the amino acids from Food A to make this protein?
14Essential vs. non-essential amino acids Can you use only the amino acidsfrom Food A to make this protein?The yellow triangle is a non-essential amino acid
15Essential vs. non-essential amino acids Can you use only the amino acidsfrom Food A to make this protein?The blue square is alimiting amino acid
16Essential vs. non-essential amino acids Can you use only the amino acidsfrom Food A to make this protein?
17Essential vs. non-essential amino acids Can you use only the amino acidsfrom Food B to make this protein?
18Essential vs. non-essential amino acids Can you use only the amino acidsfrom Foods A and B to make this protein?
19Essential vs. non-essential amino acids Did you use all of the amino acidsfrom Foods A and B to make this protein?It not, what did the body do with the extras?
20Essential vs. non-essential amino acids Foods A and B are complementary: each supplies some amino acids for the full set of needed amino acids
21Essential vs. non-essential amino acids Cannot be madeNeed to be eatenNon-essential amino acidsCan be made from others
22Conditionally essential amino acids Under certain conditions some of the nonessential amino acids cannot be made in the bodyExample: in phenylketonuria (PKU) phenylalanine cannot be converted to tyrosine thus tyrosine, a nonessential amino acid in healthy individuals, becomes an essential amino acid in people with PKU
23Protein structurePeptide bonds: join the acidic group of one amino acid with the amino group of another amino acidPolypeptides: a chain of amino acids linked by peptide bondsProteins: made of one or more polypeptide chains folded into specific three-dimensional structures
28Concept checkWhich chemical element is found in protein but not in carbohydrate or lipid?What determines whether an amino acid must be consumed in the diet?What determines the shape of a protein?How does denaturation affect protein function?
29Protein digestionProteins have to be broken down to tripeptides, dipeptides and amino acids, before they can be absorbed into the mucosal cells of the small intestineMechanical digestion of proteins starts in the mouth, continues in the stomach and the small intestineChemical digestion of proteins begins in the stomach but most of it occurs in the small intestine
30Protein absorptionIn the mucosal cells of the small intestine dipeptides and tripeptides are broken down to single amino acidsAmino acids are moved from the mucosal cells to blood by the transporting systemSince the transporting system has a limited capacity, amino acid supplements may reduce the absorption of some dietary amino acids
32ApplicationInsulin is a protein. Why do diabetics need to inject insulin rather than take it orally?
33Concept checkThe purple amino acids are absorbed by the same transport system as the green amino acids. If you consume a sports drink that is supplemented with the green amino acids what will happen to the absorption of the purple ones.nothingthe larger amount of green ones will limit the absorption of the purple onesthe small amount of the purple ones will be absorbed firstboth will be absorbed equally because the body needs them
34Concept check Where does the chemical digestion of protein begin? Why might supplementing one amino acid reduce the absorption of other amino acids?
35Amino acid poolAmino acid pool: amino acids available for use in the bodyFrom the diet or breakdown of body proteinsUsed to make other proteins or chemicals (for example: DNA, RNA, histamine, etc.)Used to provide energy or make glucose or fatty acids
36Amino acid poolAmino acids enter the available pool from the diet and from the breakdown of body proteins. Of the approximately 300 grams of protein synthesized by the body each day, only about 100 grams are made from amino acids consumed in the diet. The other 200 grams are produced by the recycling of amino acids from protein broken down in the body. Amino acids in the pool can be used to synthesize body proteins and other nitrogen-containing molecules, to provide energy, or to synthesize glucose or fatty acids.
37Protein synthesis Protein synthesis is regulated by genes Depending whether a gene is turned on (expressed) or turned off, the protein is synthesized or its synthesis stopsChemicals can turn genes on and offFor example, high iron turns on the ferritin gene to make more ferritin which is needed for iron storage
38Limiting amino acidA shortage of just one essential amino acid can stop the process of protein synthesisLimiting amino acid is the essential amino acid present in short supply relative to body’s needNonessential amino acids can be made in the body via transaminationTransamination: amino acid group from one amino acid is transformed to carbon-containing molecule to form another amino acid
41Protein functions Structure (e.g., skin, hair, muscle) Speed up chemical reactions (enzymes)Chemical signaling (e.g., hormones)Transportation of substances (e.g., blood proteins)Movement (e.g., muscles)Immunity (e.g., antibodies)Blood clottingFluid balanceMaintenance of pH
42Protein functionsStructure: Collagen, which is the most abundant protein in the body, plays important structural roles. It is the major protein in ligaments, which hold our bones together, and in tendons, which attach muscles to bones, and it forms the protein framework of bones and teeth.
43Protein functionsCatalyzing reactions: Enzymes, such as this one that speeds up the breakdown of starch, are protein molecules. All chemical reactions occurring within the body require the help of enzymes. The specific structure or shape of each enzyme allows it to interact with the molecules in the specific reaction it accelerates. Without enzymes, metabolic reactions would occur too slowly to support life.
47Protein functions Fluid balance: Blood proteins contribute to the number of dissolved particles in the blood. Since proteins are charged particles, they help attract water to keep it in the blood. If protein levels in the blood fall too low, osmosis causes fluid to leak out of the blood vessels and accumulate in the tissues, causing swelling known as edema, shown here. Proteins also regulate fluid balance because some are membrane transporters, which pump dissolved substances from one side of a membrane to the other.
48Functions of amino acids Amino acids from the diet are used to make proteins and nitrogen-containing moleculesExtra amino acids cannot be stored as proteinsExtra amino acids are used for energy or stored as fat
49Using proteins for energy When we do not consume enough calories, body proteins are broken down and amino acids used to provide energyDeamination removes amino group (NH2)Produces urea which is excreted in urineCarbon, hydrogen, and oxygen from amino acids can be converted to glucose and can be broken down to produce ATP
51Protein deficiencyProtein-energy malnutrition: loss of fat and muscle and decreased immunity from long-term protein and calorie deficienciesTypes:Kwashiorkor: pure protein deficiencyMarasmus: overall protein-energy deficiency
52Protein deficiency: Kwashiorkor Kwashiorkor, seen in this child from Haiti, is characterized by a swollen belly, which results from fluid accumulating in the abdomen and fat accumulating in the liver. Growth is impaired, but because energy intake is not necessarily low, the child may not appear extremely thin. The lack of protein also causes poor immune function and an increase in infections, changes in hair colour, and impaired nutrient absorption.
53Protein deficiency: Marasmus Marasmus, seen in this Somalian boy, ischaracterized by depletion of fat stores and wasting of muscle. It has devastating effects on infants because most brain growth takes place in the first year of life; malnutrition in the first year causes decreases in intelligence and learning ability that persist throughout the individual’s life.
54Concept checkWhy does protein synthesis stop when the supply of an amino acid is limited?How does the body know in what order to assemble the amino acids when making a protein?When is protein used as an energy source?
55High-protein dietsExcess dietary amino acids can be deaminated and converted to fatty acids and stored as triglycerides in adipose tissueIncreased urea outputIncreased demands on the kidneysIncreased loss of water from the bodyPossible increased loss of calciumIncreased risk of kidney stones
56High-protein diets Often: high in animal proteins with high saturated fat and cholesterol and low in fiberlow in grains, fruits, and vegetableshigh in calories and fatIncreased risk of heart disease, cancer, obesity, diverticulosis (outpouching of the colon wall) and diabetes mellitus
58Concept checkWhat are consequences of low or high protein diets?
59Food allergiesFood allergy: an adverse immune response to a specific food product
60Protein allergiesWhen a protein is absorbed intact, the immune system can recognize it as an antigen and start cellular reactionsThe second time immune system detects that same allergen (allergy-causing antigen), there is an allergic reactionMajor food allergens: milk, eggs, peanuts, tree nuts, fish, shellfish, soy, and wheat
61Food sensitivitiesFood intolerance or food sensitivity: an adverse reaction to food; usually does not involve production of antibodiesTriggers various symptoms after consumptionExamples:MSG symptom complex or Chinese restaurant syndromeGluten intolerance or Celiac diseaseIngestion of gluten in rye, wheat or barley triggers an autoimmune reaction against villi in the small intestines
63Protein balanceProtein intake recommendations are based on nitrogen balanceNitrogen balance: the amount of nitrogen consumed versus nitrogen excreted
64Nitrogen balanceNitrogen balance: nitrogen intake equals nitrogen lossMaintenance of body protein and weightNegative nitrogen balance: more nitrogen lost than consumedFrom illness, injury, or decreased consumptionPositive nitrogen balance: more nitrogen consumed than lostDuring growth, pregnancy, or weight training
66Recommended daily allowance (RDA): 0.8 g/kilogram of body weight for adultsWith more weight, more protein is needed for maintenance and repair70 kg (154 lb) adult = 56 g of protein/dayTypical Canadian adult consumes less than 80 g of protein/dayHigher needs in infants, children, during pregnancy and lactation (breast feeding), after injury, and in athletesPregnant/lactating women: add 25 g of protein/day
68Protein intake in athletes Endurance athletes, like triathlete Simon Whitfield, need more protein than others because some protein is used for energy and to maintain blood glucose during endurance events, such as triathlons. Endurance athletes may benefit from the daily consumption of 1.2 to 1.4 g of protein/kilogram of body weight.Andy Lyons/Staff/Getty Images SportStrength athletes, such as weight lifter Marie-Eve Beauchemin-Nadeau, need extra protein to provide the raw materials needed for muscle growth; 1.2 to 1.7 g kilogram/day is recommended.Laurence Griffiths/Staff/Getty Images Sport
70How much protein does this person need? Calculate100 pound adultweight in kilograms equals weight in pounds x0.45 kg/lbProtein RDA = 0.8 g/kilogram of body weightHow much protein does this person need?
71Choosing correct protein intake During the first year of life, growth is rapid, so a large amount of protein is required per unit of body weight. As growth rate slows, requirements per unit of body weight decrease but continue to be greater than adult requirements until age 19. What is the RDA for a 2-year-old child who weighs 14 kilograms?14 g/day15.4 g/day11.2 g/day21 g/day
72Recommended protein intake Acceptable Macronutrient Distribution Range for protein:10% to 35% of caloriesProtein quality: measure content of essential amino acids compared to body needsProtein digestibility corrected amino acid score (PDCASS): most commonly used for determining protein quality
73Protein quality High-quality, or complete dietary proteins Contain all amino acids to meet body’s needsHigher PDCASSMore easily digestedAnimal proteins and soyIncomplete dietary proteinsLower in one or more essential amino acidsMost plant proteinsCombine complementary proteins
74Complementary proteins Protein complementation: combining proteins from different sources to assure presence of all essential amino acidsExample: legumes with grains
75Complementary proteins The amino acids that are most often limited in plant proteins are lysine (lys), methionine (met), and cysteine (cys). As a general rule, legumes are deficient in methionine and cysteine but high in lysine. Grains, nuts, and seeds are deficient in lysine but high in methionine and cysteine.
76Complementary proteins Many traditional diets take advantage of complementary plant proteins, such as lentils and rice or chickpeas and rice in India, rice and beans in Mexico and South America, hummus (chickpeas and sesame seeds) in them Middle East, and bread and peanut butter (peanuts are a legume) in Canada. Complementary proteins do not need to be consumed in the same meal, so eating an assortment of plant foods throughout the day can provide enough of all the essential amino acids.Melanie Acevedo/FoodPix, Getty Images, Inc.
77Canada Food Guide Recommendations Choose variety of foods to meet body needs of the essential amino acids
79What are some menu items Get protein without too much saturated fatEat both animal and plant proteinsGo with beansWhat are some menu itemsyou could consume?
80Which foods provide the cheapest source of protein? CalculateWhich foods provide the cheapest source of protein?
81Types of vegetarian diets Vegetarian diets: plant-based diets that eliminate some or all animal foods
82Vegetarian diets Reasons to be vegetarian: Limited land and/or resourcesHealthReligionPersonal ethicsEnvironmental concernsBenefits: lower cost and healthierRisks: amino acid, mineral, and B vitamin deficiency
86Concept check How can nitrogen balance be maintained? What are benefits and risks of consuming a plant-based diet?How can vegetarians avoid nutrient deficiencies?
87Think criticallySickle cell anemia is an inherited disease caused by an abnormality in the gene for the protein hemoglobin. It causes red blood cells to take on a sickle shape.Sickle cell hemoglobin differs from normal hemoglobin by one amino acid. Why might this difference change the shape of the hemoglobin?Do you think sickle-shaped red blood cells can travel easily through narrow capillaries?How might this disorder affect the ability to get oxygen to the body’s cells?
88What are similarities and differences between: Proteins and amino acids?Plant and animal proteins?Kwashiorkor and marasmus?Vegetarian and vegan diets?
89ApplicationsWhat advice could you give to a loved one about protein consumption to decrease disease risk?
90Checking student learning outcomes How do proteins contribute to health and disease?What advice would you give to a loved one about protein consumption?