Protein
Chapter 7
Learning Outcomes
• Describe how amino acids form proteins
• Define essential and nonessential amino acids and
explain why adequate amounts of each of the
essential amino acids are required for protein
synthesis
• Distinguish between high quality and low quality
proteins and list sources of each
• Describe how 2 low quality proteins can be
complementary to each other to provide the
required amounts of essential amino acids
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Learning Outcomes
• Explain the methods used to measure the protein
quality of foods, including assessment of
biological value
• List the factors that influence protein needs.
Calculate the RDA for protein for a healthy adult
with a given body weight
• Explain positive nitrogen balance, negative
nitrogen balance and nitrogen equilibrium and list
conditions under which they may occur
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Learning Outcomes
• Describe how protein is digested and absorbed in
the body
• List the primary functions of protein in the body
• Describe how protein-energy malnutrition can
eventually lead to disease in the body
• Develop a vegetarian diet plan that meets the
body’s protein needs
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What makes proteins different
from carbohydrates and lipids?
• What elements are proteins composed of?
• What is different about their chemical
structure?
• How much energy is in protein?
• What types of foods are high in protein?
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Exchanges Lists
Food CHO (g) Protein(g) Fat(g) Kcal
Starches 15 0-3 0-1 80
Fruits 15 0 0 60
Vegetables 5 2 0 25
Meat 0 7 0-10 45-100
Fat 0 0 5 45
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Structure of Protein
• Contains hydrogen, oxygen, carbon and
nitrogen
• Comprised of amino acids
– Nitrogen group (amine)
– Acid group (carboxyl group)
– Hydrogen
– Side chain (R-portion)
• Determines protein name
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Amino Acids
• Nonessential amino acids
– Body can produce
• Conditionally essential amino acids
– Essential during infancy, disease or trauma
• Essential amino acids
– Must be taken in via food
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Synthesis of Non Essential
Amino Acids
• Transamination
– Transfer of an amine group from an amino acid
to a carbon skeleton to form a new amino acid
• Deamination
– Amino acid losing an amine group
– Amine Group is incorporated into urea in the
liver
– Excreted in urine
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Complete and Incomplete
Proteins
• Complete Proteins
– Adequate amounts of all 9 of the essential amino acids
– Animal proteins-exception gelatin
• Incomplete Proteins
– Inadequate amounts of the essential amino acids
– Plant proteins-exception soy
• Complementary Proteins
– Combining plant proteins to compensate for limiting
amino acids
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Complementary Proteins
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Synthesis of Protein
• Amino acids are
linked by peptide
bonds to form
proteins
• Synthesis of protein
determined by gene
expression
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Instructions for protein synthesis
are in the DNA genetic code
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Synthesis of Proteins (Gene Expression)
• DNA unwinds
• DNA sequence is
TRANSCRIBED (copied)
into a complementary
mRNA strand in nucleus
• DNA stays, but mRNA
travels to the cytosol
• In the cytosol the ribosomes
read the mRNA and
TRANSLATE the message
to make a specific amino
acid
• The amino acids bond to
form a protein
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Sequencing gone wrong
Sickle cell anemia Sickle cell
• The amino acid valine
(GUG) replaces glutamic
acid (GAG) in the DNA
sequence in ½ the
polypeptide chains of the
protein hemoglobin
• This changes the shape of
the protein (hemoglobin)
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Sequencing gone wrong: MTHFR
C>T (ala to val) mutation
• Thymine is in place of the
more common cytosine in
the MTHFR gene
• This results in an amino acid
change, instead of alanine
there is a valine
• This changes the structure
of the enzyme, so those with
the mutation have a less
active enzyme
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Synthesis of Protein
• Protein Organization
– Primary Structure
• Sequential order of amino acids determine shape
– Secondary Structure
• Spiral like shape determined by bonds between
amino acids
– Tertiary Structure
• 3-D configuration determines function
– Quaternary Structure
• Interaction of 2 or more polypeptides 22
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Denaturation and Adaptation
• Denaturation of Protein
– Altering protein’s 3D structure
– Acid, alkaline, heat, enzymes and agitation
• Adaptation of Protein Synthesis
– Constant state of breakdown, rebuilding and
repair
– Protein turnover
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Sources of Protein
• Diet and recycling of body protein
• North America-70% supplied by meat,
poultry, fish, milk and milk products,
legumes and nuts
• Worldwide-35% of protein comes from
animal
• How to incorporate more plant protein?
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Evaluation of Food Protein Quality
• Biological Value (BV)
– Measures how efficiently the absorbed food protein in
converted into body tissue proteins
– Nitrogen retained (g)/Nitrogen absorbed (g) * 100
– Important clinically if protein intake is limited
• Protein Efficiency Ratio (PER)
– Compares amount of wt gain by a growing lab rat vs
consuming equal amount of a reference protein
– Weight gain (g)/ Protein consumed
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Evaluation of Food Protein
Quality
• Chemical Score
– Calculate the amount of each essential amino acid in a
gram of the food divided by the “ideal” amount for that
amino acid in a gram of the reference food
– The lowest amino acid ratio for the essential amino
acids in the chemical score
• Protein Digestibility Corrected Amino Acid Score
(PDCAAS)
– Most widely used
– Chemical score x digestibility
– Most animal proteins and soy are 1.0
– Used to calculate the DV on nutrition labels 29
Recommended Intakes of Protein
• Equilibrium
– Protein intake equals protein losses
• Positive Nitrogen Balance
– Protein intake exceeds protein losses
• Negative Nitrogen Balance
– Protein losses exceed protein intake
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Protein RDA
• Adults
– .8 g/kg healthy body weight
• Recovery states
– .8 –2 g/kg body weight
• Endurance or strength athletes
– .8 –1.7 g/kg body weight
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Protein Digestion and Absorption
• Cooking denatures protein
• Stomach
– Hydrochloric acid denatures
– Pepsin begins enzymatic digestion
– Gastrin controls the release of pepsin
• Small intestine
– CCK released which stimulates release of proteases
• Amino acids absorbed into the portal vein
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Functions of Proteins
• Producing Vital Body Structures
• Maintaining Fluid Balance
– Edema
• Contributing to Acid Base Balance
– Buffers
• Forming Hormones, Enzymes and
Neurotransmitters
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Functions of Proteins
• Transporting Nutrients
• Forming Glucose
– Gluconeogenesis
– Muscle wasting is cachexia
• Providing Energy
– 4 kcal/gm
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Functions of Proteins
• Immune Function
– Innate or non specific immunity
– Acquired or specific immunity
• Role of protein
• Benefits of breastfeeding
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Health Concerns
• Protein- Energy Malnutrition (PEM)
– Marasmus
• Minimal amounts of energy, protein and other
nutrients
– Kwashiorker
• Minimal amounts of protein and moderate energy
deficit
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Food protein allergies
• When certain foods trigger an immune
response
• WBC stimulate antibodies to cause the
symptoms associated with an allergic
reaction
• Eight foods account for 90% of allergies
(peanuts, tree nuts (walnuts), milk, eggs,
fish, shellfish, soy, and wheat)
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Special Considerations: Renal
diets
• Kidney role in protein metabolism
• Early stages of renal disease: low protein
• If dialysis: high protein, low phosphorus
• Renal disease has high risk of CVD and
type 2 diabetes
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Special Considerations:
Protein Supplements
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Special Considerations: Protein bars
Protein Blend (Soy Protein Isolate, Whey Protein
% DV* Isolate, Calcium Caseinate), Glucose Syrup,
Kcal 300
Chocolatey Coating (Sugar, Fractionated Palm
Total Fat 6g 9% Kernel Oil, Cocoa, Whey, Nonfat Milk, Soy Lecithin,
Natural Vanilla Flavor), Glycerin, Maltitol Syrup,
Sat fat 3.5g 18%
Cookie Bits (Rice Flour, Sugar, Canola Oil, Alkalized
Trans Fat 0g Cocoa, Rice Starch, Baking Soda, Salt), Natural
Cholesterol 0mg 0% Flavor, Almond Butter, High Oleic Canola Oil, Soy
Lecithin, Peanut Flour, MINERALS: Calcium
Sodium 170mg 7%
Phosphate, Magnesium Oxide, Zinc Gluconate, Iron
Total Carb 38g 13% (Ferrous Fumarate), Copper Gluconate, Chromium
Aspartate, VITAMINS: Vitamin C (Ascorbic Acid),
Dietary Fiber 1g 4%
Vitamin E Acetate, Vitamin B3 (Niacinamide),
Sugars 18g Pantothenic Acid (Calcium Pantothenate), Vitamin
B6, Vitamin B2, Vitamin B1 (Thiamin Mononitrate),
Protein 23g 46%
Folic Acid, Biotin, Vitamin B12. CONTAINS
ALMOND, MILK, PEANUT AND SOY
INGREDIENTS. MADE ON EQUIPMENT
THAT ALSO PROCESSES WHEAT.
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Special Considerations: Weight loss
• High Protein diets
• VLCD
– 500-800 kcal/day, 50 grams of protein/day from
non fat milk and egg white
• Protein Sparing Modified Fast
– 1.2-1.5 grams of protein per kilogram of ideal
body weight, low fat, low glycemic index
vegetables
• Weight Loss Surgery
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– 60-80 g/day
Vegetarian Diets
• Types of Vegetarians
– Vegan, Lacto-ovo-vegetarians and Lacto-
vegetarians
• Nutrient Concerns
– Protein (BV value)
– No dairy (Calcium, D, riboflavin)
– No meat (zinc, B12, omega 3)
• Special Concerns for Infants and Children
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Food Plan for Vegetarians
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Non- meat sources of protein
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Here are some ways for vegetarians to
incorporate these nutrients into their diets:
• Iron: Eggs, fortified breakfast cereals, soy-based foods, dried prunes and apricots, nuts
beans, legumes, whole-wheat bread, and baked potatoes are rich in iron.
• Calcium, which builds bone, is plentiful in cheese, yogurt and milk. Ovo-vegetarians
and vegans can get it in soy products, legumes, almonds, sesame tahini, calcium-
fortified orange juice, and dark, leafy vegetables like collard greens and bok choy.
• Zinc, which boosts the immune system, is ample in soybeans and soymilk, veggie
"meats," eggs, cheese and yogurt, fortified breakfast cereals, nuts, breads, mushrooms,
and peas. Wheat germ and pumpkin seeds also have high zinc content
• Vitamin B12: Soy-based beverages, some breakfast cereals, and fortified veggie
"meats" are all good sources of vitamin B12
• Riboflavin: Almonds, fortified cereals, cow's milk, yogurt, mushrooms, and soy milk
are riboflavin-rich foods.
• Linolenic acid (omega-6): Canola oil and flaxseeds and flaxseed oil contain linolenic
acid, along with soybeans, tofu, walnuts, and walnut oil.
• Omega-3 Fatty Acids: Cold-water fish, such as salmon and mackerel, are high in
omega-3 fatty acids For vegetarians who do not eat fish, good sources of omega-3s are
flaxseed, walnut, soy and canola oils. Supplements are fine, too
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Vegetarian Diets
• 190 pound male, athlete, practicing a
vegetarian diet
• Protein needs?
• BF
• Lunch
• Dinner
• Snack
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