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Chapter 6

Proteins

Overview of Protein • Form important structures in body, make up key part of blood, help regulate body func9ons, can fuel body cells

• Body made up of thousands of proteins • Contains nitrogen, carbon, hydrogen, and oxygen • North Americans generally consume more than they need to maintain health

• Func9ons • Regulates and maintains body func9ons • Provides essen9al form of nitrogen (amino acids)

Amino Acids—Building Blocks of Proteins

• 20 different amino acids make up all proteins •  Analogous to leFers of the alphabet

• 9 essen9al amino acids •  Not synthesized, must be eaten in diet

• 11 nonessen9al amino acids •  Synthesized in body

• On average supply 4 kcal per gram

Essential Amino Acids

• 9 essen&al amino acids •  Cannot be synthesized by humans in sufficient amounts or at all, must be included in the diet

• Branched Chain Amino Acids • Leucine, isoleucine, and valine

•  Used by muscles for energy needs • Proteins from milk are popular with strength training athletes

• Limi&ng amino acid •  Essen9al amino acid in lowest concentra9on in food or diet rela9ve to body needs

• Condi&onally essen&al amino acids •  Amino acids made from essen9al amino acids if insufficient amounts are eaten

Protein Synthesis and Organization

• Proteins are linked together by chemical bonds, called pep9de bonds • Bonds form between amino group of one amino acid and acid (carboxyl) group of another

•  Dipep9des, 2 groups •  Tripe9des, 3 groups •  Oligopep9des, 4 to 9 groups •  Polypep9des 10 or more groups

• Most proteins are polypep9des, 50-‐2000 groups

Protein Synthesis

Protein Organization

• Order of amino acids in a protein determines its ul9mate shape

• Protein’s final shape determines its func9on in the body

Sickle Cell Anemia

•  Illness that results from malforma9on of red blood cell because of an incorrect structure in part of its hemoglobin protein chains

Denaturation of Proteins • Denatura&on

•  altera9on of a protein’s three-‐dimensional structure, because of treatment by heat, enzymes, acid, alkaline solu9ons, agita9on

• Cooking useful in aiding diges9on • Body needs the amino acids proteins in diet supply

Protein in Foods

• Average American consumed 12.2% less meat and poultry in 2012 than in 2007

• Top five food products in North American diet: • Beef • Poultry • Milk • White bread • Cheese

• Worldwide meat consump9on has been increasing, especially developing countries

Protein in Foods

MyPlate: Sources of Protein

Grains

• Bread • Breakfast cereals • Rice • Noodles

2-3 grams per serving

• Carrots • Corn • Broccoli

Vegetables Protein

• Meat • Eggs • Fish • Dry beans • Nuts

7 grams per serving

8-10 grams per serving

• Cheese • Yogurt • Milk

Dairy Fruits

• Apples • Oranges

<1 gram per serving

• Bananas

Fruits Grains

Vegetables Protein

Dairy

ChooseMyPlate.gov

Fruits Grains

Vegetables Protein

Dairy

Protein Quality of Foods

• Animal and plant proteins can differ greatly in propor9ons of essen9al and nonessen9al amino acids

• Plant proteins in grains are o`en low in one or more of the nine essen9al amino acids

• Animal protein generally contains all 9 essen9al amino acids • High-‐quality (complete) proteins

•  Dietary proteins that contain ample amounts of all nine essen9al • Lower-‐quality (incomplete) proteins

•  Dietary proteins that are low in or lack one or more essen9al amino acids •  All-‐or-‐none principle in protein synthesis

• Limi9ng amino acids • Complementary proteins

Complementary Proteins

• Two food protein sources that make up for each other’s inadequate supply of specific essen9al amino acids

• Together they yield a sufficient amount of all nine and so provide high-‐quality (complete) protein for the diet

• Example: ea9ng a diet of rice and beans or vegetables combined with nuts

A Closer Look at Plant Sources of Proteins

• Per gram many are great source of nutrients • Also contain phytochemicals • Legumes, beans, peas, and peanuts • Nuts and seeds • All contribute to protein, vitamin, fiber in meal • Health and Plant Proteins

•  Heart healthy •  Cancer-‐figh9ng •  Bone health •  BeFer glucose control •  Soy and menopausal symptoms

Food Protein Allergies •  Immune system mistakes food protein for harmful invader • Reac9ons range from mild intolerance to fatal allergic reac9ons •  Introducing allergenic foods early in life may prevent allergies • 8 foods account for 90% of food-‐related allergies; soy, peanuts, tree nuts, wheat, milk, eggs, fish, and shellfish

Digestion

• Denatured •  By cooking and acid in the stomach

• Hormone Gastrin •  Thinking of and chewing food cause release into stomach •  S9mulates the release of acid and pepsin

• Pepsin •  Enzyme produced by the stomach •  Breaks polypep9de into shorter chains of amino acids

Protein Digestion and Absorption

Digestion of Protein in the Small Intestine • Release of CCK

•  Hormone cholecystokinin • Pancrea9c enzymes:

• Trypsin, among others, into the duodenum • Pep9des à amino acids • Small pep9des and amino acids

• Ready for absorp9on Absorption of Protein in the Small Intestine

• Site of diges9on •  Microvilli surface and within absorp9ve cells lining small intes9ne

• Many different amino acid transport mechanisms • Ac9ve absorp9on • Amino acids are sent to the liver

•  Via portal vein

Gluten Sensitivity – Celiac Disease

• Protein found in certain grains, wheat, rye, barley • Incomplete gluten breakdown in small intes9ne leaving small pep9des and amino acids

• Celiac disease, inflammatory response to small pep9des and amino acids

• Autoimmune response, gene9c predisposi9on

Functions of Proteins • Building blocks of body components • Fluid balance maintenance • Acid/base balance (contribute to) • Building blocks of hormones and enzymes • Immune func9on • Forming glucose • Energy yielding (non-‐preferred source) • Contribu9ng to sa9ety

Producing Vital Body Structures

Amino-acid pool in a cell used to form body proteins and other products

• muscles • connec9ve 9ssue • mucus • blood-‐clojng factors • transport proteins in bloodstream •  lipoproteins • enzymes •  immune an9bodies

• some hormones • visual pigments • support structure inside bones

Protein Turnover

• Breakdown and synthesis • Cell responds to change • Amino acids can be recycled • During any day, an adult makes and degrades about 250 grams of protein

Maintaining Fluid Balance

Contributing to Acid-Base Balance • Proteins help regulate acid-‐base balance in blood • Proteins in cell membranes pump chemical ions in and out of cells • Keeps the blood slightly alkaline • Buffers

•  compounds that cause a solu9on to resist changes in acid-‐base condi9ons

Forming Hormones and Enzymes • Amino acids are required for synthesis of many hormones • Thyroid hormones are made from only one type of amino acid tyrosine

•  Insulin hormone composed of 51 amino acids

Contributing to Immune Function

• Key component of cells within immune system • Without sufficient dietary protein, immune system lacks material needed to func9on properly

Forming Glucose

• Without enough carbohydrate, liver produces glucose from amino acids

•  In starva9on, amino acids from muscle 9ssue are converted into glucose

• Wastes muscle 9ssue and can produce edema

Providing Energy • Proteins supply liFle energy for a weight-‐stable person • Can provide energy during prolonged exercise and during weight loss efforts

• Amino group from amino acid is removed, and remaining carbon skeleton is metabolized for energy needs

•  Increase in urea produc9on • Protein is costly source of calories

Contributing to Satiety • Provide the highest feeling of sa9ety a`er a meal • Sa&ety

•  no longer a desire to eat; a feeling of sa9sfac9on • Higher protein diets are appropriate if nutri9onally sound, being moderate in fat and having enough fiber

Synthesis of nonprotein nitrogen-containing

compounds, such as serotonin

Synthesis of body proteins for cell structure and other needed components, such

as enzymes, hormones, and muscle contractile proteins

Energy production from amino-acid carbon

skeletons for body cells: yields on average 4 kcal/g Free ammonia

(NH3)

Amino acid pool in cell

Amino acids from cell breakdown

Fat made from amino- acid carbon skeletons (liver cells only, and generally not much)

Urea synthesis in liver

Excretion of urea by the kidneys

Amino acids from diet

Glucose production from amino-acid carbon

skeletons (liver and kidney cells only)

Metabolism of

Amino Acids

Protein Needs

• Promotes protein equilibrium/balance • Es9ma9ng protein need: • 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 weight

Protein Balance

RDA for Protein • About 10% of total calories, some experts recommend up to 15% • Endurance athletes

•  May need up to 1.7 gm/kg • Provide about 8-‐10% of total kcal • Most of us eat more than the RDA for protein • Excess protein cannot be stored as protein

Protein Intake Recommendations • Dietary Guidelines for Americans 2010

•  Increase intake of fat-‐free or low-‐fat milk and milk products •  Choose a variety of protein foods (seafood, lean meat and poultry, eggs, beans, soy, nuts)

•  Increase amount and variety of seafood consumed •  Replace protein foods high in solid fats

Does Eating a High-Protein Diet Harm You?

• If low in plant foods (fiber), vitamins, phytochemicals • If high in saturated fat and cholesterol • Excessive intake of processed red meat is linked with colon cancer

• Burden on the kidney • May increase calcium loss in the urine • Increase urine produc9on – increase risk for dehydra9on

Amino-Acid Supplements

• Some9mes used by athletes and dieters • The right amount of protein will aid athle9c performance • Using amino acid supplements is not considered safe • Overwhelms absorp9ve mechanisms in small intes9ne • Excess amino acids cause toxicity

•  methionine, cysteine, and his9dine

Protein-Calorie Malnutrition

• Somewhat rare in developed countries • Seen in alcoholics

• In developing countries • Stunts growth and increase risk of infec9on

• Protein-‐Energy Malnutri9on • Marasmus

• Starva9on and insufficient protein and calories • Kwashiorkor

• Marginal amount of calories and insufficient protein

Protein-Calorie Malnutrition

Severe protein (with moderate energy)

deficit; often accompanied by infections or other diseases

Severe energy and protein deficit

• Edema

• Mild to moderate weight loss

• Maintenance of some muscle and subcutaneous fat

• Growth impairment (60%–80% of normal weight for age)

• Rapid onset

• Fatty liver

Characteristics of Kwashiorkor Characteristics of Marasmus

• Severe weight loss

• Wasting of muscle and body fat (skin and bones appearance)

• Severe growth impairment (less than 60% of normal weight for age)

• Develops gradually

Protein Calorie Malnutrition

Why Do People Become Vegetarians?

• Ethics, religion, economics, and health • Evolved over centuries from necessity to an op9onal choice • Gallup poll: 5% of U.S. adults self-‐proclaimed vegetarians • Recent survey: 12% of college students • People who choose vegetarian diet can meet nutri9onal needs • Health benefits

•  Posi9ve impact on heart health •  Contain no cholesterol •  No trans fat, liFle saturated fat •  Contain ample mono and polyunsaturated fats •  Good source of fiber, vitamins, minerals, phytochemicals

Increasing Plant Proteins in Your Diet

• Try the veggie burger • Sprinkle seeds, nuts on salad • Eat soy nuts, edamame • Peanut buFer on bagel • Choose beans with taco seasoning instead of beef or chicken for taco filler

• Use soy milk instead of dairy

Food Planning for Vegetarians

• Vegan •  Eats only plant foods

• Fruitarian •  Eats fruits, nuts, honey, and vegetable oils

• Lactovegetarians •  Plant and dairy products

• Lactoovovegetarians •  Plant products, dairy & eggs

• Concerns for infants and children

Vegan Diets

• Complementary proteins • Nutrient deficiency concerns

•  Vitamin B12 •  Iron •  Zinc •  Calcium •  Omega-‐3 faFy acids