1. Chapter 6 PROTEINS AND AMINO ACIDS

2. Sources of Protein in the Diet
Protein deficiency is rare in Canada.
The CCHS found that more than 97% of Canadians consumed protein above the AMDR.
In Canada, disappearance data suggest that about 62% of dietary protein comes from meat, poultry, fish, eggs and dairy products.
Most of the world relies on plant proteins from grains and vegetables.
As a country’s economy improves, the proportion of animal foods in the diet tends to increase.
Copyright 2012, John Wiley & Sons Canada, Ltd. 2

3. Nutrients Supplied by Plant and Animal Foods
Animal products provide sources of protein, B vitamins and minerals such as iron, zinc and calcium.
However, animal products are low in fiber and can be high in fat.
Plant sources of protein are also a good source of B vitamins, iron, zinc, fiber and calcium, but in less absorbable forms.
Copyright 2012, John Wiley & Sons Canada, Ltd. 3

4. Copyright 2012, John Wiley & Sons Canada, Ltd.
Amino Acids
Amino acids are the building blocks of protein.
Each amino acid contains a central carbon atom bound to a hydrogen atom, an amino group, an acid group and a side chain.
Essential amino acids cannot be synthesized by the human body in sufficient amounts to meet needs.
Essential amino acids must be included in the diet.
Copyright 2012, John Wiley & Sons Canada, Ltd. 4

5. Copyright 2012, John Wiley & Sons Canada, Ltd.
Amino Acids
*These amino acids are considered conditionally essential by the Institute of Medicine, Food and Nutrition Board (Dietary Reference Intakes for Energy Carbohydrates, Fiber, Fat, Protein and Amino Acids, Washington, DC: National Academies Press, 2002). See text for explanation.
Copyright 2012, John Wiley & Sons Canada, Ltd. 5

6. Amino Acids: Transamination
When a nonessential amino acid is not available from the diet, it can be made in the body by the process of transamination.
Figure 6.4 Transamination
In this example, transamination transfers the amino group from the nonessential amino acid alanine to
the carbon compound alpha-ketoglutarate to form the 3-carbon compound pyruvate and the amino acid
glutamate.
Copyright 2012, John Wiley & Sons Canada, Ltd. 6

7. Copyright 2012, John Wiley & Sons Canada, Ltd.
Protein Structure
Peptide bonds are chemical bonds that link amino acids together.
Peptide bonds are formed between the acid group of one amino acid and the nitrogen group of the next amino acid.
Dipeptide bonds are formed between two amino acids.
Polypeptides are formed between many amino acids.
A protein is made of one or more polypeptide chains folded into a three-dimensional shape.
Copyright 2012, John Wiley & Sons Canada, Ltd. 7

8. Copyright 2012, John Wiley & Sons Canada, Ltd.
Protein Structure
Figure 6.5 Protein structure
When many amino acids are linked by peptide bonds, they form a polypeptide. Folding of the polypeptide chains creates the three-dimensional structure of the protein.
Copyright 2012, John Wiley & Sons Canada, Ltd. 8

9. Protein Shape Determines Function
The final shape of a protein determines its function.
Connective tissue proteins and collagen are elongated.
Hemoglobin has a spherical shape.
If the shape of a protein is altered, its function may be disrupted.
Copyright 2012, John Wiley & Sons Canada, Ltd. 9

10. If Protein Shape is Altered, Function May Be Altered
Figure 6.6 Sickle cell anemia
In sickle cell anemia, a change in the sequence of amino acids in hemoglobin alters the shape and function of the protein molecule. Sickle cell
hemoglobin forms long chains that distort the shape of red blood cells. (Ingram Publishing/Getty Images, Ltd.)
Copyright 2012, John Wiley & Sons Canada, Ltd. 10

11. Protein Digestion and Absorption
Figure 6.8 Protein digestion and absorption
Protein must be broken down into small peptides and amino acids before it can be absorbed into the mucosal cells.
Copyright 2012, John Wiley & Sons Canada, Ltd. 11

12. Protein Digestion and Food Allergies
Food allergies are triggered when a protein from the diet is absorbed without being completely digested.
Proteins from milk, eggs, nuts, wheat, soy, fish and shellfish and peanuts are common causes of food allergies
A rapid, severe allergic reaction is called anaphylaxis.
People with GI disease are prone to allergies because their damaged intestines allow for the absorption of whole proteins.
Copyright 2012, John Wiley & Sons Canada, Ltd. 12

13. Amino Acid Pool Allows for Amino Acid Availability
Figure 6.9 Amino acid pool
Amino acids in the available pool come from the diet and from the breakdown of body proteins. They
are used to synthesize body proteins and nonprotein molecules, and to generate ATP, or to synthesize
glucose or fatty acids.
Copyright 2012, John Wiley & Sons Canada, Ltd. 13

14. Protein Synthesis: Transcription and Translation
1 In the nucleus, the blueprint, or code, for the protein is copied or transcribed from the DNA gene
into a molecule of messenger RNA (mRNA).
2 The mRNA takes the genetic information from the nucleus to structures called ribosomes in the
cytosol, where proteins are made.
3 In the cytosol, transfer RNA (tRNA) reads the genetic code and delivers the needed amino acids to
the ribosome to form a polypeptide chain.
Figure 6.10 Transcription and translation
DNA in cell nuclei provides the information needed to assemble proteins (transcription and translation).
Copyright 2012, John Wiley & Sons Canada, Ltd. 14

15. Energy Production from Protein
1 The amino group is removed by deamination.
2 Deamination of some amino acids produces 3-carbon molecules that can be used to synthesize glucose, via gluconeogenesis.
3 Deamination of some amino acids results in 2-carbon molecules that form acetyl-CoA, which can enter the citric-acid cycle or
be used to synthesize fatty acids.
4 Deamination of some amino acids forms molecules that are intermediates in the citric-acid cycle.
5 High-energy electrons from the breakdown of amino acids are transferred to the electron transport chain where the energy is
trapped and used to produce ATP and water.
Figure 6.12 Amino acid metabolism
In order for the body to use amino acids as an energy source, the nitrogen-containing amino group must be removed. The
compounds remaining after the amino group has been removed are composed of carbon, hydrogen, and oxygen and can be
broken down to produce ATP or used to make glucose or fatty acids.
Copyright 2012, John Wiley & Sons Canada, Ltd. 15

16. Copyright 2012, John Wiley & Sons Canada, Ltd.
Protein Functions
Enzymes speed up metabolic reactions.
Transport proteins move substances in and out of cells.
Antibodies help the immune system in fighting off foreign bodies.
Contractile proteins help the muscles to move.
Hormones are chemical messengers, such as insulin and glucagon.
Proteins help to regulate fluid and acid-base balance.
Copyright 2012, John Wiley & Sons Canada, Ltd. 16

17. Copyright 2012, John Wiley & Sons Canada, Ltd.
Protein Deficiency
Protein-energy malnutrition (PEM) is a term that covers a range of protein deficiency conditions that may include only protein deficiency or protein deficiency plus energy deficiency.
Kwashiorkor is a pure protein deficiency.
Marasmus is an energy deficiency.
Copyright 2012, John Wiley & Sons Canada, Ltd. 17

18. Copyright 2012, John Wiley & Sons Canada, Ltd.
Protein Excess
Elevated protein intakes over long periods of time can result in:
Hydration and kidney function issues
Bone health issues
Increased risk of heart disease and cancer
Copyright 2012, John Wiley & Sons Canada, Ltd. 18

19. Proteins that May Harm Certain Individuals: Phenylketonuria
PKU is an inherited condition attributed to a defective gene.
Aspartame, a sugar substitute, contains phenylalanine.
Figure 6.18 Phenylketonuria
In individuals with phenylketonuria, phenylalanine accumulates and is converted to phenylketones, which can interfere with brain development.
Copyright 2012, John Wiley & Sons Canada, Ltd. 19

20. Labelling for Allergies
Health Canada has identified the following food allergens: peanuts, tree nuts, sesame seeds, milk, eggs, fish (including crustaceans and shellfish), soy, wheat and sulphites.
These products are responsible for 90% of reported adverse reactions to food.
Food manufacturers are required to clearly state if a product contains any of the priority food allergens.
Copyright 2012, John Wiley & Sons Canada, Ltd.

21. Labelling for Allergies
The 3 ways allergens can appear on the label:
Listed in the ingredient list
Identified in a parenthetical statement
With use of the word “contains.”
Health Canada has published a booklet entitled Common Food Allergies: A Consumer’s Guide to Managing the Risks.
Copyright 2012, John Wiley & Sons Canada, Ltd.

22. Copyright 2012, John Wiley & Sons Canada, Ltd.
Nitrogen Balance
Figure 6.20 Nitrogen balance
Nitrogen balance indicates whether the amount of protein in the body is remaining constant, decreasing, or increasing.
(Cameron Lawson/NG Image Collection; Brian Yarvin/Photo Researchers; Roy Toft/NG Image Collection)
Copyright 2012, John Wiley & Sons Canada, Ltd. 22

23. Determining Protein Requirements
Copyright 2012, John Wiley & Sons Canada, Ltd. 23

24. Calculating Protein Requirements
Following the recommendations of Canada’s Food Guide will result in a diet that includes both animal and plant sources of protein.
A Food Guide serving of milk will provide 8 g of protein.
Serving of beans 7 to 10 g of protein.
Serving of meat 14 to 20 g of protein.
Serving of grains or vegetables 1 to 3 g of protein.
Copyright 2012, John Wiley & Sons Canada, Ltd. 24

25. Protein Labelling Claims
Copyright 2012, John Wiley & Sons Canada, Ltd.

26. Considering Protein Quality
Figure 6.22 Protein digestibility-corrected amino acid score (PDCAAS)
The PDCAAS of plant proteins is generally lower than that of animal proteins. An exception is soy protein.
Source: Protein Quality Evaluation, Report of the Joint FAO/WHO Expert Consultation, FAO/WHO, 1989.
Copyright 2012, John Wiley & Sons Canada, Ltd. 26

27. Considering Protein Quality
Copyright 2012, John Wiley & Sons Canada, Ltd. 27

28. Protein Content of CFG Food Groups
Figure 6.24 Protein content of Canada’s Food Guide food groups
Meats, legumes, eggs, and milk products contain the most protein per serving.
Copyright 2012, John Wiley & Sons Canada, Ltd. 28

29. Meeting Protein Needs with a Vegetarian Diet
A healthy vegetarian diet can be achieved by modifying selections from Canada’s Food Guide.
Servings of vegetables, fruits and grains will remain the same.
Meat and Alternatives group contains– dried beans and peas and nuts and seeds.
Substitute for the dairy foods fortified soy milk.
Copyright 2012, John Wiley & Sons Canada, Ltd. 29

30. Meeting Protein Needs with a Vegan Diet
Figure 6.26 Combining Plant Proteins
Combining complementary sources of incomplete plant proteins can provide a diet containing enough of all the essential amino acids. (Jean Paul
Chassenet/Photo Researchers; Corbis Images; © istockphoto.com/Luca Manieri)
Copyright 2012, John Wiley & Sons Canada, Ltd. 30

31. Meeting Nutrient Needs with a Vegan Diet
Copyright 2012, John Wiley & Sons Canada, Ltd. 31

32. Copyright 2012, John Wiley & Sons Canada, Ltd.
Copyright © 2012 John Wiley & Sons Canada, Ltd. All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein. .
Copyright 2012, John Wiley & Sons Canada, Ltd. 32