1. Protein

2. Introduction to Protein
Protein’s Primary Jobs
Structure
Muscles, tendons, & ligaments
Skin & hair
Blood & tissues
Working proteins
Enzymes
Antibodies
Transport vehicles
Hormones
Protein’s Secondary Job
Energy = 4 kcal/g

3. Amino Acids: The Building Blocks of Protein
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Body uses 20 amino acids to make proteins
Consist of:
Central Carbon
Amino group (NH2)
Acid group (COOH)
Side Chain (R-group)

4. Examples of amino acids
©2001 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
Examples of amino acids

5. Classification of Amino Acids
Essential
Body can’t make, must come from diet
Nonessential
Body can make
Conditionally essential
Becomes essential due to inadequate availability or disorder of metabolism
Ex: PKU makes tyrosine essential

6. Classification of Amino Acids

7. Primary Structure of Proteins
# & sequence of amino acids
Amino acids bound in peptide bonds = polypeptide
Determines protein’s physical & chemical properties and its function
Like letters in alphabet make words

8. Sickle Cell Anemia
Disease caused by single error in amino acid sequence of hemoglobin
Red blood cells rigid, sticky, shaped like a sickle
Signs
Anemia, pain in chest, abdomen & joints, swollen hands & feet, frequent infections, stunted growth, vision problems

9. Secondary Structure of Protein
Polypeptide strand forms coils and folds because of chemical attractions between individual amino acids

10. Structure of Proteins Tertiary Structure Quaternary Structure
folds and loops of coils
Quaternary Structure
The union of several polypeptides in a protein
Ex:hemoglobin

11. Protein Synthesis
mRNA = messenger RNA
tRNA = transfer RNA

12. Protein Breakdown & Digestion
Denaturation = disruption of shape
Heat --- cooking (ex: frying egg)
Acids/bases --- chemicals in digestive system
Salts of heavy metals --- toxins (ex: mercury)
Goal of digestion is to liberate amino acids so body can reconfigure them

13. Protein Digestion Stomach Small intestine
HCl and enzyme gastrin break up protein strands
Small intestine
Numerous enzymes break down polypeptide strands into smaller di- and tripeptides.
Amino acids absorbed through intestinal wall

14. Food Allergies When larger polypetides are absorbed
Body’s immune system responds
Side effects
Mild rashes
Swelling of throat &
airways

15. Sources & Quality of Amino Acids & Proteins in Diet
Protein Sources:
Meat, Poultry, Fish
Eggs
Dairy products
Legumes, soy
Nuts
Complete vs incomplete
Quality Score
PDCAAS = protein digestibility corrected amino acid score
-used by DRI committee in evaluating people’s protein intakes
-scale 100 to 0, re digestibility and aa ratios compared to human need
Egg whites, ground beef, chicken, tuna, skim milk score 100
soy scores 94. Lower in methionine
most legumes 50-60, incomplete

16. Protein Complementation
Combining foods with incomplete proteins to provide adequate amounts of all essential amino acids
Examples:
Rice & beans
Corn & beans
Photo 6.2

17. Functions of Amino Acids & Protein in Body
Water diffusees freely across membranes, but proteins too big to pass through cell walls or blood vessels. Protein attracts water, and thereby plays a role in fluid balance in body compartments.

18. Protein and Energy Use of Amino Acids During Times of Need:
--Glucogenic amino acids
--Cells can oxidize amino acids
Use of Amino Acids in Times of Abundance
--Amino acids redirected from gluconeogenesis & ATP pathways
--Converted to lipids

19. RDA for Protein 0.8 g protein/kg body weight Increases during
Infancy
Pregnancy
Lactation
Do athletes need more?
Do vegetarians need more?

20. Protein in Sports Nutrition
Increased protein or AA intake alone does not trigger muscle growth
Exercise is required stimulus!
Research:
Studies based on nitrogen balance; methods controversial
Novel training increases protein needs
As fitness improves, protein needs return to baseline
Accepted ranges:
Endurance athletes: g/kg
Strength athletes: g/kg

21. Vegetarian Diets Types Lactovegetarian Lacto-ovo-vegetarian Vegan
Include milk
Lacto-ovo-vegetarian
Include milk & eggs
Vegan
No animal products whatsoever

22. Additional Guidelines for Protein Intake
Natl. Acad Sci Inst. of Med. recs:
10-35% of energy
Assumes kcal intake is sufficient
DGAs & MyPyramid
Fat-free or low-fat milk
2-7 oz. lean meat
Legumes cups
Problem with excess?
Prob w/ excess:
High protein intakes accompanied by:
Fat, Saturated fat, Cholesterol – CVD risk
Colorectal cancer & red meat & processed meats
If liver or kidney disease present, excess protein damaging
May be contraindicated in bone health