1. Chapter 6 Proteins and Amino Acids: Function Follows Form

2. Why Is Protein Important?
Major component of all plant and animal issues
Vital to many aspects of health
Provide energy and help keep skin, hair, and nails healthy
Deficiency leads to wasting
Excess protein intake a greater problem in the U.S.

3. Amino Acids Are the Building Blocks of Proteins
Proteins are sequences of amino acids (AA)
20 different amino acids
9 essential amino acids
Body cannot make them
Must get them through diet
11 nonessential amino acids
Do not need to be supplied by diet
If body cannot make them, categorized as conditionally essential amino acids

5. Amino Acids as Building Blocks
Amino acid structure
One central carbon atom
One hydrogen atom (H)
One carboxylic acid group (-COOH)
One amino group (-NH2)
One side group unique to each amino acid
Side group gives the amino acid its identity

6. Protein Structure Amino Acid Sequence
Each amino acid is joined to the next by a peptide bond
Peptide bonds
Dipeptide (2 AA)
Oligopeptide (3 AA)
Polypeptide (4-10 AA)

7. Protein Structure Protein Shape
Sequence and properties of AA determines protein shape
Shape determines protein’s function

9. Protein Denaturation Denaturation Disrupts shape
Protein unfolds and loses its shape (denature)
Caused by acidic or alkalinity, high temperature, alcohol, oxidation, and agitation

10. Functions of Body Proteins
Each protein has a specific function determined by its unique shape

11. Functions of Body Proteins
Structural and mechanical functions
Collagen
Most abundant
Gives skin and bone their elastic strength
Keratin
Primary constituent of hair and nails
Motor proteins
Turn energy into mechanical work

12. Functions of Body Proteins
Immune functions
Antibodies
Blood proteins that attack and inactivate bacteria and viruses
Part of the body’s immune response

13. Functions of Body Proteins
Enzymes
Catalyze, or speed up, chemical reactions
Every cell contains thousands of types of enzymes

16. Functions of Body Proteins
Hormones
Regulate body processes
Acid-base balance
Proteins help maintain stable pH levels by acting as buffers
Acidosis or alkalosis occurs when proteins unable to fulfill buffer function

17. Functions of Body Proteins
Transport functions
Proteins act as
Channels and pumps, allowing substances to flow through membranes
Carriers, transporting important substances in the blood stream

18. Functions of Body Proteins
Fluid Balance
Fluids found inside and outside cells
Inside cells: intracellular fluid
Outside cells: extracellular
Two types:
Interstitial fluid (between cells)
Intravascular fluid (in the blood)

19. Functions of Body Proteins
Fluid Balance
Blood proteins maintain appropriate fluid levels in vascular system
Edema results when diet lacks enough protein to maintain normal levels of blood proteins
Edema: Swelling caused by buildup of fluid between cells

21. Functions of Body Proteins
Source of Energy and Glucose
Carbohydrates and fat are protein-sparing
Body prefers burning them for energy
Will resort to burning protein for energy if necessary
Body readies protein for use as energy through deamination
Removal of amino group from an amino acid

22. Protein Digestion and Absorption
In the stomach
Proteins are denatured by hydrochloric acid
Pepsin begins digestion
10–20% of digestion
In the small intestine
Proteases and intestinal lining cells break down large peptides into smaller peptides

24. Protein Digestion and Absorption
Undigested Protein
Pass out of the body in feces
Diseases of the intestinal tract cause problems with digestion by decreasing absorption efficiency
Celiac disease
Cystic fibrosis

25. Protein Digestion and Absorption
Amino Acid and Peptide Absorption
Travel via portal vein to liver  released into general circulation

26. Protein in the Body Protein Synthesis
AA assembled in specific sequence
Draws on AA pool as needed
Dispensable AA missing
Cell will make that AA or obtain it from the liver

27. Protein in the Body Protein Synthesis Draws on AA pool as needed
Indispensable AA missing
Body may break its own protein down to supply the missing AA
Indispensable AA unavailable
Protein synthesis halts and partially completed protein used elsewhere in the body

28. Protein in the Body Amino Acid Pool and Protein Turnover The AA pool
Available AA
Protein synthesis; produce energy and glucose
Protein turnover
Constant recycling of protein

29. Protein in the Body Synthesis of Nonprotein Molecules
Amino acids as precursors of DNA, RNA, and coenzymes
Also used to make neurotransmitters:
Chemicals that send signals from nerve cells to other parts of the body

30. Protein in the Body Protein and Nitrogen Excretion
Breakdown of amino acids
Removes nitrogen (amino) group
Amino groups converted to urea for excretion

31. Protein in the Body Nitrogen Balance
Nitrogen intake vs. nitrogen output
Nitrogen equilibrium
Nitrogen intake = nitrogen output
Healthy adults

32. Protein in the Body Positive nitrogen balance
Nitrogen intake > nitrogen output
Growth; recovery from illness
Negative nitrogen balance
Nitrogen intake < nitrogen output
Injury and illness

34. Protein in the Diet Recommended Intakes of Protein
Adult RDA = 0.8 gram per kilogram of body weight
Severe physical stress can increase body’s need for proteins
Infections, burns, fevers, surgery increase protein losses
Diet must replace lost protein

35. Protein in the Diet Protein Consumption in the United States
Generally higher than recommended range

36. Protein in the Diet Protein Quality Complete Proteins
Supply all indispensable amino acids
Animal proteins; soy proteins
Incomplete and Complementary Proteins
Low in one or more indispensable amino acids
Most plant proteins

37. Protein in the Diet Protein Quality Complementary proteins
Two incomplete proteins can equal a complete protein
One makes up for the other’s lack of specific essential amino acids
Combination then provides sufficient amounts of all essential amino acids

39. Protein in the Diet Protein Quality
Evaluating Protein Quality and Digestibility
Provides all the indispensable amino acids at amounts the body needs
Provides enough other amino acids to serve as nitrogen sources for making dispensable amino acids
Should be easy to digest
Consider the protein digestibility-corrected amino acid score (PDCAAS)

40. Protein in the Diet Proteins and AAs as Additives and Supplements
Protein and AA additives
Structure, texture, and taste of foods
Protein and AA supplements
Used for a variety of reasons: dieters, athletes, certain diseases
Risks unknown

41. Vegetarian Eating Why People Become Vegetarians
Various reasons, including
Religious beliefs
Environmental concerns
Aversion to eating another living creature
Concerns about animal cruelty concerns
In some cases a necessity

44. Vegetarian Eating Health Benefits of Vegetarian Diets
Less fat, saturated fat, and cholesterol intake
More magnesium and folate
More antioxidants
More fiber and phytochemicals
Reduces risk for heart disease, obesity, hypertension, and cancer

45. Vegetarian Eating Health Risks of Vegetarian Diets
Vegan diets may be low in some nutrients
Calcium, iron, zinc, vitamin D, and vitamin B12
Higher intake of phytates
More restrictive food choices = less nutrients
Careful planning needed for growth and overall health

46. Vegetarian Eating Dietary Recommendations for Vegetarians
Choose a variety of foods
Choose whole, unrefined foods
Choose a variety of fruits and vegetables
Choose lower-fat dairy products and eggs in moderation
Consume a regular source of vitamins B12 and D
Fortified foods or supplements

48. Health Effects of Too Little or Too Much Protein
Protein-Energy Malnutrition
Kwashiorkor
Edema and other signs
Between ages of 18 and 24 months
Associated with extreme poverty

49. Health Effects of Too Little or Too Much Protein
Protein-Energy Malnutrition
Marasmus
Chronic PEM
Infants and 6- to 18-month-old children
Adults with cancer or starvation

50. Health Effects of Too Little or Too Much Protein
Health Effects of Excess Dietary Protein
Kidney function
Increases kidney filtration rate, straining function
Mineral losses
Link between high-protein diet and osteoporosis

51. Health Effects of Too Little or Too Much Protein
Health Effects of Excess Dietary Protein
Obesity
Correlation with body fat
Heart disease
Increased saturated fat and cholesterol intake
Cancer
Increased risk for certain types of cancer