1. CH 6: Proteins

2. Proteins
Consider last as protein is the body’s least desirable source of energy
4 kcal/gram
When body uses protein for energy it is not available to perform other critical functions
No protein stores – all protein has a function in the body
We’ll come back to this soon

3. Chemical Nature of Proteins
Proteins are made from amino acids (aa)
There are 20 different aa
Amino acids all contain: C, H, O, N
Carbs and lipids do not contain N
Cannot make protein from carbs and lipids
Each aa has an amino group, an acid group, a hydrogen atom, and a side group.
It is the side group that makes each amino acid unique.

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5. Chemical Nature of Proteins
Proteins are chains of amino acids (a.a.) joined by peptide bonds
Order of the a.a. is determined by your DNA
The sequence of amino acids in each protein determines its unique shape and function.
For the protein to function the amino acids must be in the correct order and the chain must fold up properly

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7. © 2008 Thomson - Wadsworth

8. Amino Acids
The body cannot make 9 of the amino acids – these are the essential amino acids
These amino acids must be supplied by the diet
The body can make 11 of the amino acids
These are the nonessential a.a.
Some amino acids are conditionally essential, required under certain conditions
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9. Amino Acids
Diet must provide all 9 of the essential a.a. on a regular/daily basis for proteins to be made
Need all 20 a.a. to make most proteins
Animal sources of proteins contain all 9 essential aa (one exception, gelatin)
Plant sources are missing or low in at least one essential aa (one exception, soy)

10. Protein Intake Recommended level of intake is expressed 2 ways:
10 – 25 % daily caloric intake
0.8 grams protein per kg body weight (RDA)
Computer programs use this value
Most meet this level EASILY

11. Protein Function page 223
Growth, maintenance, and repair of body tissue
Need protein to make muscles, skin, hair, blood vessels……..
Cannot grow without protein
Replace lining of GI tract every 3 days (maintenance example)

12. Protein Function Enzymes
Enzymes are proteins that catalyze (speed up) chemical reactions
Every reaction in the body requires a specific enzyme

13. Protein Function Hormones Hormones are chemical messengers
Travel to target cells/organs and ilicit a response
Examples:
Insulin and glucagon
Growth hormone
Thyroxin – regulates metabolic rate

14. Protein Function Antibodies Component of immune system
Attack foreign substances in the body

15. Protein Function Transportation of Substances
Proteins are needed to transport lipids in the blood
Proteins are needed to transport substances across cell membranes
Need for nerve and muscle contraction
Proteins are needed to absorb calcium and iron

16. Protein Function Fluid Balance – page 222 Proteins attract water
Proteins are too big to pass through plasma membranes or out of capillaries
Water moves between the compartment
If protein levels in the blood drop, water leaks out of the blood into surrounding tissues  edema

17. Protein Function
Edema occurs when there are inadequate plasma proteins
This occurs when:
Liver disease
Inadequate protein/food intake
Kidney disease  blood proteins excreted
Injury breaks open cells

18. Protein Function Acid Base Balance Proteins can act as acids and bases
Help keep body fluids at a safe pH
Serve as buffers in the body

19. Protein Function Energy 4 kcal/gram
Use as a source of energy when glucose/glycogen stores are empty

20. Amino Acids
The body regularly breaks down proteins and remakes them or uses them for energy as needed – page 224
If an essential a.a. is missing the body cannot make all of the proteins it needs
Hair and nails may grow more slowly
Immune system compromised (antibodies are proteins)

21. Nitrogen Balance pg 225 Positive Nitrogen Balance
Making more protein than breaking down
Anabolism > catabolism
Pregnant women
Infants and children
Athletes (building muscle)
Recovering from surgery, injury, or illness

22. Nitrogen Balance Negative Nitrogen Balance
Breaking down more protein than you are making
Catabolism > anabolism
Illness, fever
Burn victims
Starvation/anorexia

23. Nitrogen Balance/Equilibrium
In Zero Nitrogen Balance
Protein made = protein broken down
Anabolism = catabolism
Most healthy adults are in nitrogen balance/equilibrium

24. Protein in the Diet Complete Proteins Food Sources
Contain all 9 essential a.a. in adequate amounts
Food Sources
Most animal sources of protein are complete proteins (exception is gelatin)
Meat, poultry, fish, eggs, dairy
Soy products (plant source of complete protein)

25. Protein in the Diet Incomplete Proteins Food Sources
Lack or are low in 1 or more of the essential a.a.
Food Sources
Most plant sources are incomplete proteins
Nuts, seeds, legumes, grains, and vegetables
Gelatin

26. Protein in the Diet Complementary Proteins
Two or more protein sources that together provide all 9 of the essential a.a.
Most combinations of at least 2 categories of plant proteins will complement each other
Seeds and nuts (with legumes)
Grains (with legumes)
Legumes (with seeds, nuts, grains)
Vegetables (with grains, nuts, seeds)

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28. Protein in the Diet
Examples of meals/foods containing complementary proteins:
Rice and beans
…..

29. Protein Digestion Digestion Mouth Stomach
Protein is denatured by hydrochloric acid.
Pepsinogen is converted into its active form pepsin by hydrochloric acid.
Pepsin chemically breaks proteins into smaller polypeptides

30. Protein Digestion In the Small Intestine
Pancreatic enzymes (proteases) digest protein into short peptide chains called oligopeptides, which contain four to nine amino acids.
SI enzymes (peptidases) split proteins into amino acids.

31. Protein Absorption
Amino acids are absorbed into the cells of the SI and enter the blood
Amino acids are transported to the liver for processing