Chapter 06

Proteins

Overview of ProteinOverview of Protein

• Body is made up of thousands of proteins

• Contains nitrogen, carbon, hydrogen, and oxygen

• Functions– Regulates and maintains body functions– Provides essential form of nitrogen (in the

form of amino acids)

Structure of Amino AcidsStructure of Amino Acids

Amino AcidsAmino Acids

• 20 different amino acids make up all proteins

– analogous to letters of the alphabet

• 9 essential amino acids

• 11 nonessential amino acids

Relationship of Essential and Relationship of Essential and NonNon--essential Amino Acidsessential Amino Acids

•• Example:Example:Phenylalanine Phenylalanine tyrosinetyrosine(essential (essential ------ nonnon--essential)essential)

•• But in PKU diagnosed individuals:But in PKU diagnosed individuals:Phenylalanine tyrosinePhenylalanine tyrosine

(essential (essential ---------- NOW essential) NOW essential)

X

Classification of Amino AcidsClassification of Amino Acids

Protein SynthesisProtein Synthesis

• DNA contains coded instructions

• Copies of codes – Transferred to the cytoplasm (via mRNA)

• Amino acids added one at a time – With aid of transfer RNA (tRNA)

• Requires energy

Protein SynthesisProtein Synthesis

Protein OrganizationProtein Organization

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

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

Protein OrganizationProtein Organization

Sickle Cell AnemiaSickle Cell Anemia

DenaturationDenaturation of Proteinsof Proteins

Heat/acid/alkaline/enzymesHeat/acid/alkaline/enzymesResults in alteration of the proteinResults in alteration of the protein’’s s

threethree--dimensional structuredimensional structure

Protein in FoodsProtein in Foods

My Plate:Sources of Protein

Grains

• Bread• Breakfast cereals• Rice• Noodles

2-3 grams perserving

2-3 grams perserving

• Carrots• Corn• Broccoli

Vegetables Protein

• Meat• Eggs• Fish• Dry beans• Nuts

7 grams perserving

8-10 grams perserving

• Cheese• Yogurt• Milk

DairyFruits

• Apples• Oranges

<1 gram perserving

• Bananas

Fruits Grains

VegetablesProtein

Dairy

ChooseMyPlate.gov

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Fruits Grains

VegetablesProtein

Dairy

(eggs, beans): © IT Stock/PunchStock RF; (milk): © Ingram Publishing/SuperStock RF

Dietary ProteinDietary Protein• High-quality

– Complete

• Low-quality

– Incomplete

• All-or-none principle in protein synthesis

• Limiting amino acids

• Complementary proteins

Animal ProteinAnimal Protein

• Contribution to our diet

– ~70% of our protein intake

• Top 5 contributors of protein in U.S. diet:

– Beef– Poultry– Milk– White bread– Cheese

• Worldwide, 35% comes from animal sources

Health and Plant ProteinsHealth and Plant Proteins

• Heart healthy

• Cancer-fighting

• Bone health

• Better glucose control

• Soy and menopausal symptoms

Plant SourcesPlant Sources

• Provide protein, minerals, and dietary fiber

• Contain no cholesterol

• Limited saturated fats

• High fiber

– Time needed to adjust to the higher fiber load

Complementary ProteinComplementary Protein

Food 1 Food 2 CombinedFood 1 Food 2 Combined

CC CCCCCC CCCCAAAA AA CAR AAAA AA CAR CARCAR CARCARRRR RRR RRRRRR CAR CAR CARCAR CARCAR

Digestion of Protein in the StomachDigestion of Protein in the Stomach

• Denatured

– By cooking and acid in the stomach

• Gastrin

– Stimulates the release of acid and pepsin

• Pepsin

– Breaks down proteins

DenaturationDenaturation

Protein Digestion and AbsorptionProtein Digestion and Absorption

Digestion of Protein in the Small IntestineDigestion of Protein in the Small Intestine

• Release of CCK

• Pancreatic enzymes:

– Trypsin, among others, into the duodenum

• Peptides amino acids

• Small peptides and amino acids•

– Ready for absorption

Protein AbsorptionProtein Absorption

• Site of digestion

– Microvilli surface and within absorptive cells

• Many different amino acid transport mechanisms

• Active absorption

• Amino acids are sent to the liver

– Via portal vein

Protein TurnoverProtein Turnover

• Breakdown and synthesis

• Responds to change

• Amino acids can be recycled

Functions of ProteinsFunctions of Proteins•• Building blocks of body componentsBuilding blocks of body components

•• Fluid balance maintenanceFluid balance maintenance

•• Acid/base balance (contribute to)Acid/base balance (contribute to)

•• Building blocks of hormones and enzymesBuilding blocks of hormones and enzymes

•• Immune functionImmune function

•• Forming glucoseForming glucose

•• Energy yielding (nonEnergy yielding (non--preferred source)preferred source)

•• Contributing to satietyContributing to satiety

Fluid BalanceFluid Balance

Metabolism of Amino AcidsMetabolism of Amino AcidsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Synthesis of nonproteinnitrogen-containing

compounds, such asserotonin

Synthesis of body proteinsfor cell structure and otherneeded components, such

as enzymes, hormones, andmuscle contractile proteins

Energy production fromamino-acid carbon skeletons

for body cells: yields onaverage 4 kcal/g Free

ammonia(NH3)

Amino acidpool in cell

Amino acids fromcell breakdown

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

Urea synthesisin liver

Excretion of ureaby the kidneys

Amino acidsfrom diet

Glucose productionfrom amino-acid carbon

skeletons (liver andkidney cells only)

Protein BalanceProtein Balance

RDA for ProteinRDA for Protein

•• Promotes equilibriumPromotes equilibrium

•• 0.8 gm of protein / kg of healthy body weight0.8 gm of protein / kg of healthy body weight154 lb.154 lb. = 70 kg= 70 kg2.2 kg/lb.2.2 kg/lb.

70 kg x 70 kg x 0.8 g protein 0.8 g protein = 56 g protein= 56 g proteinkg healthy body weightkg healthy body weight

RDA for ProteinRDA for Protein• Increased by ~10-15 gm /day for pregnancy

• Endurance athletes

– May need 1.2 – 1.7 gm/kg healthy weight

• 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 RecommendationsProtein 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 proteins foods high in solid fats

Is a HighIs a High--Protein Diet Harmful?Protein Diet Harmful?

• Low in plant foods (fiber), vitamins, phytochemicals

• 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 production – increase risk for dehydration

MalnutritionMalnutrition

• Protein-Energy Malnutrition

• Marasmus

– Seen in hospitalized patients

• Kwashiorkor

Protein Calorie MalnutritionProtein Calorie MalnutritionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Severe protein (with moderate energy)

deficit; often accompaniedby infections orother diseases

Severe energy andprotein deficit

• Edema

• Mild to moderate weight loss

• Maintenance of somemuscle andsubcutaneous fat

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

• Rapid onset

• Fatty liver

• Severe weight loss

• Wasting of muscle and body fat(skin and bonesappearance)

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

• Develops gradually

Protein Energy Malnutrition

Characteristics of MarasmusCharacteristics of Kwashiorkor

(Kwashiorkor): © Kevin Fleming / Corbis; (Marasmus): © Peter Turnley / Corbis

Vegetarian DietsVegetarian Diets

• Why become a vegetarian?

• Vegans

• Fruitarians

• Lactovegetarians

• Lactoovovegetarians

• Concerns for infants and children

Vegetarians = Vegetarians = People who eat plantPeople who eat plant--based dietsbased diets

Types of Vegetarians

• Lactovegetarian• Consumes milk and milk products

• Ovovegetarian• Consumes eggs

• Lactoovovegetarian• Consumes eggs and milk and milk products•

• Vegan• Consumes only plant foods

Note: carnivore – herbivore - omnivore

Vegan DietsVegan Diets

• Complementary proteins

• Nutrient concerns

– Vitamin B12– Iron– Zinc– Calcium– Omega-3 fatty acids

Complementary ProteinsComplementary Proteins

Combining Complementary ProteinsCombining Complementary Proteins• Mixing plant foods with different amino acids• This will provide all essential amino acids

– no animal proteins required

• To assure an adequate mix of proteins, combine one or more foods from at least two different food groups:

– Legumes (peas, peanut butter, soy beans, other beans– Grains (wheat, rice, oats, barley, corn)– Tree nuts and seed (cashews, pistachios, sesame seeds,

sunflower seeds, pumpkin seeds)

– Amino acids often low or limiting in plant proteins:• tryptophan, threonine, lysine, and methionine

Complementary Dishes

Insert couscous photo from page 209

Peanut Butter (legume) on Bread (grain)

Couscous (grain) with Chickpeas (legume)

Complementary Protein DishesComplementary Protein Dishes

•• Insert Table 7.3 Insert Table 7.3

Is Vegetarianism a Healthy Lifestyle?

Pros• Compared to

nonvegetarians, vegetarians tend to:– Weigh less – Have less heart disease

(eat less saturated fat and cholesterol)

– Often exercise more, meditate for relaxation, and avoid tobacco and alcohol

Cons• If diets are poorly

planned, vegetarians may lack:– Kilocalories– High-quality protein– Omega-3 fatty acids– Vitamins B-12 and D– Zinc, iron, and calcium

Vegetarian Children and Teens

Children• May be difficult to consume adequate protein and

energy, because plant foods tend to be filling– Growth rates of vegan children need close

monitoring. Teens

Pro: Can be healthy diet because more fruits and vegetables are consumed

Con: May be at risk of anorexia nervosa, an eating disorder

Vegetarian Women

Pregnancy• May need vitamin B-12 supplements

– Infant could be deficient in B-12

Breastfeeding• Breastmilk may be deficient in vitamin B-12

– Infant may develop severe developmental delays if fed breast milk that lacks vitamin B-12