1. Chapter 7: Proteins

2. Major building blocks Much of the body is made of protein
17% of total body weight
Mostly muscle tissue/lean body tissue
Contain nitrogen (amino acids)
What do amino acids contain?

3. Amino Acid
NH O
R C C OH H
R group Acid group
Amine group

4. Tyrosine
Serine
Proline
Valine
Glycine
Tryptophan
Glutamine
Threonine
Glutamic acid
Phenylalanine
Cysteine
Methionine
Aspartic Acid
Lysine
Asparagine
Leucine
Arginine
Isoleucine
Alanine
Histidine
Nonessential AA
Essential AA

5. Amino acids 9 essential amino acids 11 non-essential amino acids
Cannot be made by the body, must come from diet
Found in foods that come from animal sources
Plant proteins may be combined to make complete proteins containing these essential amino acids
11 non-essential amino acids
Body can make these amino acids from essential amino acids or as long as there is sufficient nitrogen

6. Making an Essential Amino Acid
Phenylalanine Tyrosine
(Essential AA) phenylalanine hydroxyase (Nonessential AA)

7. Phenylketonuria Phenylalanine Tyrosine
(Essential AA) phenylalanine hydroxyase (Nonessential AA)
“ MISSING; LACKING”
Control Intake Becomes essential

8. Synthesis of Nonessential Amino Acids
Transamination
Addition of an amino grp to a carbon skeleton to form a new non-essential amino acid.
Deamination
The removal of an amino group from an amino acid
Occurs during protein metabolism

9. Synthesis of Nonessential Amino Acid
Transamination and Deamination

10. Functions of Proteins in Our Diet
Provide the 9 essential amino acids
Provide the nonessential amino acids or nitrogen to make the nonessential amino acids
Protein have many functions
Regulate and maintain body functions
Cell repair
Supply energy (4 kcal/g)

11. Quality of Protein High quality protein or complete protein
Contains ample amount of all 9 essential AA
Animal proteins: contain all EAA in sufficient quantities
Low quality protein
Deficient or low in one or more essential AA
Plant proteins (except Soybean)
All-or-none principle
Diet must supply all 9 EAA for protein synthesis

12. Limiting Amino Acid CCCCC AAAAAAAA CAR CAR CAR RRRRRR CAR CAR R A A A
The EAA in lowest conc in a diet relative to body needs. C is the limiting amino acid in this example
CCCCC AAAAAAAA CAR CAR CAR RRRRRR CAR CAR R A A A

13. Complementary Proteins
Food 1 Food 2 CC CCCC AAAA AA CAR CAR CAR RRR RRR CAR CAR CAR

14. Complementary Protein: (Table 7.2)
Mixed diets provides high quality protein because a complimentary protein pattern results
Essential amino acids must be 40% of total protein intake for infants and pres-school children
Diets need careful planning
For adults; EAA -11% of total pn intake

15. Complementary Protein: (Table 7.2)
Beans (legumes)
Grains Nuts/seeds
Vegetables

16. Protein Organization Peptide bond Dipeptide Tripeptide Oligopeptide
SH SH
CH CH2
H O CH H2O H O CH
H N C OH H N C OH H N C N C OH
CH H O CH H O
CH H2O CH3
Peptide bond
Dipeptide
Tripeptide
Oligopeptide

17. Protein Synthesis

18. Turnover and Metabolism

19. Protein turnover
Protein turnover – the degradation and synthesis of endogenous protein.
When proteins break down, they free amino acids to join the general circulation…what happens next?
Recycled to make new proteins (or other Ncontaining compounds) OR
– Nitrogen is removed and remaining part of amino acid is used for energy (Deamination: NH2 is removed to make urea)

20. Summary of Protein Synthesis in the Body
• DNA in nucleus of cell acts as a template
• mRNA from cytoplasm of cell enters nucleus
• Portion of DNA unwinds and mRNA matches up with it to transcribe the pattern
• mRNA leaves nucleus and goes to cytoplasm of cell
• mRNA hooks onto ribosomes
• tRNA brings in single amino acids one-at-a-time
• Amino acid placed on mRNA where so directed by template (called translation)
• Amino acids enzymatically joined into a protein
• Protein is released into cell fluid

21. When an essential amino acid (EAA) is missing, protein synthesis stops, and the remaining amino acids are deaminated and the nitrogen is excreted in the urine.
Vegetarians must pay CLOSE attention to protein complementation so as to not be deficient in any EAA!

22. Protein Organization Primary structure Secondary structure
Sequence of AA; affects protein’s shape
Related to sickle cell anemia (fig 7.3)
Secondary structure
Bends and folds held together by bonds
Formed by interactions of AA at various positions
Tertiary structure
3-D shape: affects function of protein
Quaternary structure
2 or more proteins interacting together

23. Denaturation of Proteins
Heat/acid/alkaline/enzymes
Result in alteration of the protein’s three dimensional structure

24. Digestion of Protein in the Stomach
Proteins are denatured by the cooking and the stomach acid
Gastrin (hormone) stimulates the release of pepsinogen and acid from cells in the stomach
Pepsinogen is converted to pepsin by the acid in the stomach
Pepsin (an enzyme produced in the stomach) breaks down proteins into peptones

25. Digestion of Protein in the Small Intestine
Partially digested pns from stomach stimulate the release of CCK (cholesystokinin)
Causes pancreas to release the protein splitting enzymes: trypsin, chymotrypsin, and carboxypeptidase into the duodenum
The enzymes will break peptones into smaller peptides and amino acids
Peptides and amino acids are ready for absorption

26. Protein Absorption (fig 7.7)
Active absorption
Whole proteins are broken down at the microvilli surface and within the absorptive cells
Whole proteins are eventually broken down to amino acids
Many different amino acid transport mechanisms
Amino acids are sent to the liver via portal circulation

27. Protein Digestion and Absorption Mouth
– no enzymatic digestion taking place; mechanical breakdown of proteins taking place
Stomach
HCl acid uncoils the large protein molecule so that Pepsin can begin to break the protein chain apart into smaller polypeptides, tripeptides, and dipeptides
Gastrin is released in the stomach to stimulate HCl acid production

28. Protein Digestion & Absorption Cont.
• Small Intestine
In the lumen, pancreatic and intestinal proteases break polypeptides into smaller tripeptides, dipeptides, and amino acids
At the brush border, intestinal tripeptidases and dipeptidases break down the tripeptides and dipeptides, respectively into amino acids for absorption
Note: these enzymes are “amino-acid” specific
Amino acids are absorbed into blood stream
most of the absorption takes place in the lower part of the small intestine

29. Functions of Proteins Building blocks of body components
Muscle, connective tissue, mucus, blood clotting factors, bone,
Collagen, actin, myosin, hemoglobin, keratin
Maintain fluid balance
Albumins and globulins – blood proteins
Prevent excessive build up of fluid in the extracellular spaces
Reduces risks of edema
Contribute to acid/base balance
Maintenance of normal pH in blood
Act as buffers: regulate ion concentration blood and cells

30. Functions of Proteins Building blocks for hormones and enzymes
Immune function: antibodies
Lack of protein leads to anergy: reduced immune function
Gluconeogenesis
Formation of glucose
Energy yielding

31. Functions of Proteins in the Body
Growth and Maintenance (collagen, muscle)
Formation of enzymes
Fluid balance – proteins attract water
Acid/base balance – act as buffers
Antibody formation
Hormone synthesis
Act as transport protein
Blood clotting – fibrin, collagen
Vision – opsin
Stored as fat if consumed in excess!

32. Measuring protein utilization and nitrogen balance (fig 7.9)
Protein not used is deaminated
Nitrogen is excreted in urine
16% of protein molecule is N
Normally N intake = N out
Positive N balance : N in> N out
Growth, pregnancy, building muscles
Negative N balance
Wasting of body tissues
Loss of weight

33. RDA for Protein Promotes equilibrium
0.8 gm of protein / kg of healthy body weight
154 lb = 70 kg
2.2 kg/lb.
70 kg x g protein = 56 g protein
kg healthy body wt

34. RDA for Protein Increased by ~10-15 gm /day for pregnancy
Endurance athletes may need gm/kg healthy weight
About 8-10% of total kcals
Most of us eat more than the RDA for protein
Excess protein cannot be stored as protein
The Food and Nutrition Board does not support any higher needs

35. Is a High-Protein Diet Harmful?
Likely to limit fruits and veg. and decrease fiber, vitamins, phytochemicals
Intake of animal protein increases risk for heart disease (high in saturated fat)
Excessive intake of red meat is linked with colon cancer
Burden on the kidney; need additional fluid to secrete N. may result in dehydration
Increase calcium loss
National Academy of Sciences recommends no more than 2 x RDA for protein

36. Individual Amino Acid (AA) Supplement
Supplement may cause imbalances and toxicity (especially with methionine and tyrosine)
Body is designed to handle whole proteins
Supplement can overwhelm the absorptive mechanism
Excess of one AA can hamper absorption of other AAs

37. Vegetarian
Without animal proteins, a diet can be deficient in essential amino acids –
Complete protein (animal) –
contains all of the amino acids essential in human nutrition in amounts adequate for human use
Incomplete protein (plant) –
limiting amino acid -EAA in the shortest supply, relative to the amounts needed for protein synthesis
Complementary proteins –
proteins that have different amino acid profiles, but when put together, resemble that of a complete protein source

38. Types of Vegetarians Semi-vegetarian – Lactovegetarian –
some animal products, included in diet such as poultry and fish
Lactovegetarian –
will consume milk products in the diet
Ovo-vegetarian –
will consume eggs in the diet
Lacto-Ovo vegetarian
– will consume milk and eggs in the diet
Strict Vegetarian (vegan)
– no animal sources consumed, only foods of plant origin

39. Protein Complementation
Combine cereal grains + legumes
Combine legumes + seeds & nuts
Rice + Beans
Peanut butter + Bread
Chili + Cornbread
Split pea soup + Sesame crackers

40. Protein Sources Supplies protein in abundance:
Meats
Milk and dairy products
Supplies a moderate amount of protein:
Vegetables
Breads & Cereals
Supplies NO protein:
Fruits
Fats

41. Vegetarianism: Plant Protein
Somewhat less efficient (than animal protein)
No cholesterol and low in saturated fat
High in (soluble) dietary fiber, phytochemicals
Lacking in one or more essential amino acid

42. Soy Protein Similar to animal protein (used in school lunches)
High in linoleic & a-linolenic acid
Contains Ca for bone health
Lowers blood cholesterol
Contains isoflavones (genistein and diadzein)
plantlike estrogen
Sources: tofu, soy milk, soy flour, tempeh, miso
Recommend 2-4 servings a week
Not recommended for women WITH breast cancer (or family history)

43. Evaluation of Protein Quality
Ability to support body growth and maintenance
Measured under the condition that the amount of protein consumed is < body’s needs
Protein exceeding this amount becomes less efficient
Egg protein – has the highest quality protein; used as the “standard” from which all proteins in food are measured.

44. Biological Value
Biological Value – the amount of protein nitrogen that is retained for growth and maintenance,
expressed as a percentage of the protein nitrogen that has been digested and absorbed; a measure of protein quality
Measure protein (AA) retention
Nitrogen retained
Nitrogen absorbed
BV =
X 100

45. Protein Efficiency Ratio
Used by FDA to set standards for baby food
Compares the weight gained in a growing rat after 10 days or more eating a standard amount of protein
Measures BV (protein retention)
PER =
Gram weight gain
Gram protein consumed

46. Chemical Score of Protein
Amount of each essential AA in a gram of protein in the food divided by an “ideal” amount for that essential AA
The lowest AA score is the C.S. for that food
Chem. Score
Mg of ess. AAn per gm of protein
Required mg needs of the ess. AAn per gm of protein =

47. Protein Digestibility Corrected AA Score (PDCAAS)
Most widely used (on food labels)
Maximum value is 1.0 (= milk, eggs, soy protein)
PDCAAS = Chem. Score x (~ )
Range of digestibility of that
protein

48. Malnutrition Protein-Energy Malnutrition
Marasmus: disease of starvation
Seen in hospitalized patients
Kwashiorkor
Protein Malnutrition

49. Kwashiorkor Low protein density diet Energy needs are marginally met
Signs and symptoms:
Apathy, listlessness, failure to grow, poor weight gain, change in hair color, nutrient deficiency, flaky skin, fatty infiltration in the liver, massive edema in the abdomen and legs

50. Marasmus Starving to death Insufficient protein, energy, nutrients
“skin and bones” appearance
Little or no subcutaneous fat
Reduce brain growth