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Chapter 6 – Protein: Amino Acids
Learning Objectives
After completing Chapter 6, the student will be able to:
6.1 Recognize the chemical structures of amino acids and proteins.
6.3 Describe how the body makes proteins and uses them to perform various roles.
a. Explain the process used by the body to synthesize new proteins.
6.4 Explain the differences between high-quality and low-quality proteins, including notable food sources of
each.
a. Discuss the factors used to evaluate protein quality.
Assignments and Other Instructional Materials
The following ready-to-use assignments are available in this chapter of the instructor’s manual:
• Case Study 6-1: Protein Adequacy
• New! Case Study 6-2: Amino Acid Supplements
• Worksheet 6-1: Significance of Amino Acids
1
• Worksheet 6-2: Nitrogen Balance Calculations
• Worksheet 6-3: Quick Protein Intake Assessment
2
• New! Worksheet 6-4: Chapter 6 Crossword Puzzle
3
• Worksheet 6-5: Proteins from Foods (Internet Exercise)
• New! Critical thinking questions with answers
100
Lecture Presentation Outline
4
Key to instructor resource annotations (shown to the right of or below outline topics):
TRA = Transparency acetates: 13e = 13th edition, 12e = 12th edition, 11e = 11th edition, 10e = 10th edition
I. The Chemist’s View of Proteins
A. Amino Acids – Explain amino acids, including: 10e TRA 58, 59; IM WS 6-1
1. Unique Side Groups (Figure 6-1 and 6-2)
2. Nonessential Amino Acids
3. Essential Amino Acids
4. Conditionally Essential Amino Acids
B. Proteins – Explain proteins, including: 10e TRA 60
1. Amino Acid Chains
2. Primary Structure—Amino Acid Sequence – The sequence of amino acids varies greatly (Figure 6-4)
3. Secondary Structure—Polypeptide Shapes
4. Tertiary Structure—Polypeptide Tangles
6. Protein Denaturation – Explain protein denaturation
a. Proteins can be denatured by heat and/or acid
b. After a certain point, cannot be reversed
II. Digestion and Absorption of Proteins
A. Protein Digestion – Explain the digestion of protein in the following anatomical areas (Figure 6-6):
1. In the Stomach
a. Protein is denatured by hydrochloric acid
b. Pepsinogen
III. Proteins in the Body
A. Protein Synthesis – Explain the process of protein synthesis (Figure 6-7) 10e TRA 61
1. Synthesis is unique for each human being
2. Delivering the Instructions
a. Transcription
101
b. Translation
3. Lining Up the Amino Acids – Transfer RNA lines up the amino acids
B. Roles of Proteins – Discuss the roles of proteins, including:
1. As Structural Materials
a. Matrix
b. Collagen
c. Tissue replacement.
5. As Acid-Base Regulators
a. Acids
b. Bases
c. Buffers
7. As Antibodies
a. Fight antigens
b. Provide immunity
8. As a Source of Energy and Glucose – If needed
C. A Preview of Protein Metabolism
1. Protein Turnover and the Amino Acid Pool
a. Protein turnover
b. Amino acid pool
2. Nitrogen Balance IM WS 6-2
3. Using Amino Acids to Make Other Compounds
4. Using Amino Acids for Energy and Glucose
5. Using Amino Acids to Make Fat
6. Deaminating Amino Acids (Figure 6-11)
a. Nitrogen-containing amino groups are removed
b. Ammonia and keto acids
7. Using Amino Acids to Make Proteins or Nonessential Amino Acids
102
b. Transamination (Figure 6-12)
8. Converting Ammonia to Urea – Ammonia and carbon dioxide are combined in the liver to make urea
(Figure 6-13) 10e TRA 78
9. Excreting Urea (Figure 6-14) 10e TRA 79
IV. Protein in Foods
A. Protein Quality
1. Digestibility – Depends on protein’s food source
a. Animal proteins 90%-99% absorbed
b. Plant proteins 70%-90% absorbed
c. Soy and legumes 90% absorbed
B. Complementary Proteins 10e TRA 64; IM HN 6-1
1. Combining plant foods that together contain all the essential amino acids
2. Used by vegetarians
V. Health Effects and Recommended Intakes of Protein IM CS 6-1, WS 6-5
A. Health Effects of Protein
1. Protein Deficiency 10e TRA 65
2. Heart Disease
3. Cancer – A high intake of animal protein is associated with some cancers
4. Adult Bone Loss (Osteoporosis)
a. High protein intake associated with increased calcium excretion
b. Inadequate protein intake affects bone health also
c. Ratio of calcium intake to protein intake may determine whether Ca loss is significant
5. Weight Control
6. Kidney Disease
B. Recommended Intakes of Protein IM WS 6-3; Website HN 6-2
1. 10%-35% energy intake
2. Protein RDA
103
C. From Guidelines to Groceries IM CA 6-3
1. Protein Foods
3. Fruits, Vegetables, and Grains – Small amounts in vegetables and grains
D. Read Food Labels
1. Explain how to read the protein content on a food label
1. Many reasons for supplements
VI. Highlight: Nutritional Genomics (Figure H6-1)
A. A Genomics Primer – Define and explain: 12e TRA 12, 13; 11e TRA 15
1. DNA (Figure H6-2)
2. Chromosomes
3. Nucleotide bases
B. Genetic Variation and Disease (Figure H6-3)
1. Small differences in individual genomes
2. May affect the results of dietary modifications intended to manage/treat a disease
C. Clinical Concerns
1. An increased understanding of the human genome may impact health care by:
a. Increasing knowledge of individual disease risks
b. Individualizing treatment
104
Case Studies
5
Case Study 6-1: Protein Adequacy
Erin is a 28-year-old professional woman who is 5 feet 8 inches tall and vigilantly maintains her weight at 118
pounds by following a lacto-ovo (non-fat milk and egg whites only) vegetarian diet that supplies approximately
1200 calories a day. With her understanding that protein should provide between 10 and 35 percent of her daily
calories, she reasons that her daily intake of 40 grams of protein from milk, eggs, legumes, and nuts is adequate for
her needs. She is concerned, however, that she has been sick more than usual and has experienced two stress
fractures in her leg over the past three years while exercising.
1. Explain why Erin’s assumptions about her protein needs are unrealistic based on her current weight.
2. Assuming a healthy weight for Erin is 141 pounds, use the information from the “How to” feature (p. 187) in
this chapter to calculate her recommended daily protein requirement. Show your calculations.
3. What percentage of Erin’s current energy intake comes from protein? Remember that protein provides
approximately 4 kcalories per gram.) Is this adequate? Why or why not?
4. Erin’s energy needs for a healthy weight are closer to 1600 calories a day. How might her low calorie intake
influence her protein status and possibly contribute to her current health issues?
5. How would you explain to Erin how her low intake of calories and protein contribute to her risk for
osteoporosis?
6. Assuming Erin consumes 20 grams of protein from whole grains, vegetables, and legumes each day, calculate
how she can meet the remainder of her protein needs with dairy foods and egg whites.
Answer Key
1. Protein needs are based on “healthy body weight.” Erin is underweight so her actual weight is not a good
parameter for calculating her protein needs. In addition, her total kcal intake is so low that a protein intake near
the low end of the 10-35% range is less than her protein requirement based on her current weight.
Case 6-2: Amino Acid Supplements
Danielle F. is a 78-year-old retired school teacher who is seeking ways to increase her protein intake. She does very
little cooking and avoids fish, poultry, and meat for personal reasons. She eats eggs occasionally but relies more on a
liquid amino acid product that claims to contain essential and non-essential amino acids in “naturally-occurring
amounts.”
Danielle decides to compare the protein quantity and quality of this product to an egg. Initially she learns that 1
whole egg contains 18 amino acids (9 essential amino acids and 9 non-essential amino acids). ½ teaspoon of liquid
amino acid product contains 16 amino acids (9 essential amino acids and 7 non-essential amino acids). Then she
examines the Nutrition Facts label for these two products. (See below.)
5
Contributed by Barbara Quinn.
105
Egg Nutrition Facts
Amino Acid Supplement Nutrition Facts
Nutrition Facts
Serving Size 1 egg (50g)
Servings Per Container 12
Amount Per Serving
Calories 70
Calories from Fat 45
% Daily Value*
Total Fat 5g
8%
Protein 6g
13%
Vitamin A 6%
•
Vitamin C 0%
Calcium 2%
•
Iron 4%
Vitamin D 10%
•
Thiamin 0%
Riboflavin 10%
•
Vitamin B6 4%
Nutrition Facts
Serving Size 1/2 tsp (2.5mL)
Amount Per Serving
Calories 0
Calories from Fat 0
% Daily Value*
Total Fat 0g
0%
1. Danielle notices that protein is measured differently on the two Nutrition Facts labels. Knowing that 1 gram =
1000 milligrams, what can Danielle learn about the protein quantity of one serving of liquid amino acid as
compared to one whole egg?
2. Approximately how many teaspoons of liquid amino acid would Danielle need to eat every day to receive the
amount of protein in one egg? (Notice that the nutrition information for this product is for a ½ teaspoon
serving.)
3. Looking at the Nutrition Facts label, what other important nutrients besides protein will Danielle find in an egg
that are not present in her amino acid supplement?
4. What is the sodium content of an egg compared to one serving of the liquid amino acid product?
5. According to information in this chapter, what is the safest way for Danielle to obtain the protein and amino
acids she needs? Why?
6. What precautions should Danielle take regarding the use of amino acid supplements?
Answer Key
1. ½ teaspoon liquid amino acid = 310 milligrams or 0.31 grams protein. 1 egg = 6 grams or 6000 milligrams
protein. The egg provides over 19 times the protein as the supplement.
106
Suggested Classroom Activities
Newcomers to nutrition too often think that improving nutritional status is simply a matter of introducing more
nutrients into the body. Some people think it is like dropping pennies into a jar—the more you put in, the more will
be there. They need to appreciate the enormous compensating ability of the body before they can understand how
little (or how much) nutrients affect nutritional status.
Classroom Activity 6-2: Demonstration of Diffusion and Active Transport
7
Key concept: Transfer of molecules across a membrane Class size: Any
Materials needed: Balloons (quantity = ½ the number of students)
Instructions: Divide the class physically in half with a space down the center (the cellular membrane). Demonstrate
diffusion by giving half the class small balloons to bounce up in the air (an area of higher concentration). A line of
students can then be placed in the “membrane” space to demonstrate how active transport assists in the process of
transferring the “molecule” balloons.
Classroom Activity 6-3: Protein Options (Meal Comparison)
8
Key concept: Applying protein recommendations to food choices Class size: Any
Instructions: Present the three dinner meal plans below to students and use the discussion questions to prompt them
Discussion questions:
1. Calculate the protein needs for a 25-year-old female who weighs 110 pounds using the RDA of 0.8 g/kg. Which
of the dinner meal plans would provide at least 50% of her daily need for protein? How does this illustrate how
easy it is to consume excess protein?
2. Which of the meal plans is primarily high-quality protein? Low-quality protein?
3. How can you modify the meal plans for vegetarians so that they fit the vegetarian meal plans reviewed in
Chapter 1?
4. Does the protein content of any of the foods surprise you?
Answer key:
1. 0.8 g/kg × 50 kg = 40 grams protein. Each meal provides greater than 50% of her daily need for protein. It is
1% milk, 1 cup
102
8
12
0.07
Totals
685
39.9
70
4.03
Dinner #2 Menu Item
Cal
Pro
CB
Fe
Frittata with spinach, potatoes & leeks, 1/6 of 10” pie
185
12.5
18.9
3.0
Corn, ½ cup
72
2.5
16
0.33
Totals
590
28.3
93.2
3.98
Key: Cal = kcalories, Pro = protein (grams), CB = carbohydrate (grams), Fe = iron (milligrams)
Classroom Activity 6-4: Protein Content of Over-the-Counter Protein and Amino Acid Supplements
Key concepts: Protein sources; protein/amino acid supplements Class size: Any
Instructions: Protein powder supplements are marketed as providing substantial amounts of protein and enhancing
athletic performance. Instruct students to go to the grocery or drug store and record the following regarding the
protein powder supplements they locate: name of supplement, cost of supplement, recommended daily dose, protein
content of suggested dose, and the percent of the DV for protein per serving/dose. Discuss in class and generate
suggestions for more safe, effective, enjoyable, and economical choices through food intake.
How To “Try It” Activities Answer Key
How to Calculate Recommended Protein Intakes
The student should first determine the weight to use: her or his weight in kg if within the healthy BMI range, or if
not, then the weight at the midpoint of the healthy BMI range for a person of her/his height. The student should then
multiply her or his weight in kg by 0.8 g/kg (or 0.85 g/kg if only 17 or 18 years old) to determine the protein RDA.
For example, a 19-year-old student who is 5’6” and weighs 115 lb. (BMI = 18.6) would use his/her current weight
and calculate an RDA of 42 g protein per day.
Study Card 6 Answer Key
1. The primary structure of a protein is determined by the sequence of amino acids. The secondary structure of
proteins is determined by weak electrical attractions within the polypeptide chain. As positively charged
hydrogens attract nearby negatively charged oxygens, sections of the polypeptide chain twist into a helix or fold
6. Enzymes are proteins that facilitate chemical reactions without being changed in the process (catalysts). As
facilitators, enzymes help to break down substances, build substances (such as bone), and transform one
7. In the body, amino acids can be used to make body proteins or other nitrogen-containing compounds, or they
can be stripped of their nitrogen and used for energy (either immediately or stored as fat for later use).
Deamination is the removal of the amino (NH2) group from a compound such as an amino acid—the first step
11. In general, plant proteins are lower quality than animal proteins, and plants also offer less protein (per weight or
measure of food). For this reason, many vegetarians improve the quality of proteins in their diets by combining
12. a
13. Selecting too many protein-rich foods may crowd out fruits, vegetables, and whole grains, making the diet
inadequate in other nutrients. A high-protein diet may contribute to the progression of heart disease. Foods rich
in animal protein also tend to be rich in saturated fats, and there is a correlation between animal-protein intake
fired meats and dairy products) and heart disease. On the other hand, substituting vegetable protein for animal
14. In setting protein recommendations, the authorities consider the two reasons the body needs dietary protein:
First, dietary protein is the only source of the essential amino acids, and second, it is the only practical source of
nitrogen with which to build the nonessential amino acids and other nitrogen-containing compounds the body
15. Branched-chain amino acid supplements may be beneficial for individuals with certain conditions such as liver
disease. Tryptophan may be effective for inducing drowsiness in insomniacs, but caution is still advised. For
16. b 17. d
Critical Thinking Questions
9
1. What characteristics account for the complexity of proteins as a macronutrient as compared with carbohydrates
and lipids?
2. How would you explain to an individual the role of protein in the development of edema?
3. Compare the nitrogen balance state of a healthy adolescent female, aged 16, with that of a 45-year-old, healthy
male adult.
4. What is the significance of increased high-quality protein consumption in the American diet? Are there any
dietary strategies to enhance quality protein consumption other than direct consumption of high-quality
proteins?
5. The relationship between protein and health is complex. Functional protein deficiency states can lead to
significant disease processes, and yet there is also clinical evidence that certain proteins may be linked to the
development of chronic conditions such as cardiac disease. How can protein be considered to be both beneficial
and detrimental at the same time?
6. How would you provide adequate dietary protein for an individual diagnosed with renal disease?
Answer Key
1. Even though the body must break down all macronutrients into constituent parts to facilitate energy metabolism,
proteins are more complex in nature when compared to carbohydrates and lipids. In terms of chemical structure
and composition, proteins contain nitrogen, unlike carbohydrates and lipids. The side group attached to the
2. The serum level of protein in the body plays a critical role in the regulation of water balance. If there are protein
deficiencies, fluid is more likely to shift from intravascular into interstitial spaces, resulting in a physiological
mechanism that leads to the cyclical presence of edema. This is because serum proteins such as albumin attract
110
3. An adolescent female would be considered to be in a positive nitrogen balance state due to the fact that the
4. The ingestion of high-quality proteins in the diet enables the body to effectively utilize all essential amino acids.
High-quality proteins are digested more easily as compared to low-quality proteins. High-quality proteins, by
5. The genetic expression of protein is a basic requirement of life. Protein assumes various roles in the body that
are critical to life, such as: growth, structure, enzymes, hormones, fluid/electrolyte/acid-base balance, transport,
immune function (antigen/antibodies), and as an energy source. If there are differences in protein sequencing,
various abnormalities can occur. Protein deficiency states throughout the life cycle can result in various
6. Renal impairment can lead to altered ability to eliminate waste products of metabolism. As protein contains
nitrogen as a unique element, the consumption and breakdown of this nutrient can be affected by the kidney’s
inability to excrete urea. Buildup of nitrogenous end-products of metabolism can affect all body systems,
IM Worksheet Answer Key
Worksheet 6-1: Significance of Amino Acids
Client
Essential
Non-essential
Conditionally
Required
Sequencing Error
Newborn baby
diagnosed with PKU
X
↑ Phenylalanine
X
↓ Tyrosine
X
Autosomal recessive
disorder
Elderly female
diagnosed with PEM
X*
Variable amino
acids levels seen →
usually decreased
X*
Variable amino
acids levels seen →
usually decreased
X*
Variable amino
acids levels seen →
usually decreased
Worksheet 6-2: Nitrogen Balance Calculations
1a. 135/2.2 = 61 kg; 61 0.8 g/kg = 49 g
Worksheet 6-3: Quick Protein Intake Assessment – Answers will vary.
Worksheet 6-4: Chapter 6 Crossword
1. nutrigenomics
4. calcium
7. antibodies
10. genetic information
Worksheet 6-5: Proteins from Foods (Internet Exercise)
1. b 2. a
112
Worksheet 6-1: Significance of Amino Acids
Amino Acid Concept
Application
Essential
Must be provided to the body in that form; absence is incompatible with life
Non-essential
Can be made by the body using other sources
For each of the following clinical examples, indicate whether the client is at risk to develop a problem related to
amino acids.
Client
Essential
Non-Essential
Conditionally
Required
Sequencing Error
Newborn baby
diagnosed with PKU
113
Worksheet 6-2: Nitrogen Balance Calculations
Nitrogen Balance Studies
Nitrogen Balance (NB) = Nitrogen Intake (NI) – Nitrogen Loss (NL)
NB > -5 g/day = severe stress
NB = 0 to -5 g/day = moderate stress
For each of the following examples:
a. Calculate the client’s recommended protein intake.
1. 45-year-old female, weight 135 lbs., protein intake of 38 grams and UUN = 8 grams
a.
2. 89-year-old male, weight 142 lbs., protein intake of 69 grams and UUN = 6 grams
a.
b.
c.
d.
114
Worksheet 6-3: Quick Protein Intake Assessment
Most people in the United States and Canada receive more protein than they need. This is not
surprising considering the abundance of food eaten and the central role meats hold in the North
American diet. Using a 1-day food diary, estimate your protein intake for the day. Multiply the
number of servings you consumed by the estimated protein per serving to guesstimate your total
protein intake.
Food group
Amount consumed
Estimated protein
Totals
Grains
3 grams/ounce
Vegetables
2 grams/cup equivalent
The protein RDA for young adults (19 to 24 years old) is 46 grams for women and 58 grams for
men. Health experts advise people to maintain moderate protein intakes—between the RDA and
twice the RDA.
1. Do you receive enough, but not too much, protein daily?
2. How often do you select plant-based protein foods?
115
Worksheet 6-4: Chapter 6 Crossword Puzzle
1
2
3
4
5
6
7
8
9
10
11
12
Across:
Down:
10. DNA contains the _____ that tells the body how to
assemble proteins.
12. Refers to amino acids that the body is able to
manufacture
disassembled into amino acids
4. Increased dietary protein intake can lead to
insufficient dietary _____ are consumed.
6. What the body uses to assemble its own proteins
8. Proteins that provide sufficient quantities of
essential amino acids are referred to as _____.
9. What happens when proteins are exposed to heat or
acid such as stomach acid
116
Worksheet 6-5: Proteins from Foods (Internet Exercise)
On the website, click on Protein to answer questions 1 through 3.
1. Complementary proteins, when combined, do not include all of the essential amino acids.
a. True
b. False
2. Research studies have refuted the idea that foods must be eaten at the same meal to achieve the concept of
3. Match the amount of protein with the food selection.
a. ½ cup of milk
b. 3 ounces of meat
c. 1 cup of dry beans
4. The daily adult RDA requirement for protein is 0.8 g/kg.
a. True
b. False
5. Proteins can be used interchangeably in the body because they have similar structures.
6. Yogurt is an example of an incomplete protein.
7. The Daily Value for protein is 50 grams.
