Protein

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Protein

• Chapter 6

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Protein Quiz

• A diet high in protein is usually low in fat.
• It is not possible to consume a diet too high in
  protein.
• A recommended serving size of meat is 2 -3 oz.
• Only essential amino acids are required for
  normal body processes.
• High-protein diets enhance muscle development in
  people who work out a lot.

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Chemists View of Proteins

• C -- 4 bonds
• O -- 2 bonds
• H -- 1 bond
• N -- 3 bonds

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Chemists View, Continued

• Amino Acids have 4 things in common
• Amino group (NH2)
• Acid group (COOH)
• Hydrogen attached to central C (C-H)
• Side group (R) attached to central C
• Proteins are built from amino acids

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Figure 6-1 (1Page182
Amino Acid Structure
Side group varies
Amino group
Acid group
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Chemists View, Continued

• Amino Acid chains linked by peptide bonds
• Dipeptide (2)
• Tripeptide (3)
• Polypeptide (10 or more)
• Protein dozens to hundreds of amino acids

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Protein Shape

• Shape of protein determines function
• Side group (R group) can be
• Charged - Attracted to water (hydrophilic)
• Neutral - Repelled by H2O (hydrophobic)
• Coiled twisted chains help provide stability
• Condensation
• 2 AA ---gt dipeptide H2O

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Figure 6-3Page 183
Condensation of Two Amino Acids to Form a
Dipeptide
amino acid
Amino acid
Dipeptide

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Figure 6-4Page 184
Amino Acid Sequence of Human Insulin
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Figure 6-5Page 184
The Structure of Hemoglobin
One of the four highly folded polypeptide
chains that forms the globular hemoglobin protein
Iron
Heme, the nonprotein portion of hemoglobin, holds
iron
The amino acid sequence determines the shape of
the polypeptide chain
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Figure 6-8Page 189
Sickle Cells Compared with Normal Red Blood Cells
Sickle-shaped blood cells
Normal red blood cells
Amino acid sequence of normal hemoglobin Val
His Leu Thr Pro Glu Glu Amino acid
sequence of sickle-cell hemoglobin Val His
Leu Thr Pro Val Glu
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Protein Stability, Continued

• Denaturation
• Loss of function due to a change in shape of
  protein by
• Heat
• Egg cooking (change in egg white protein)
• Acid
• Curdling of milk
• Agitation
• Whipping egg whites (meringue)

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Digestion of Protein

• Mouth
• No significant digestion
• Stomach
• HCl denatures proteins which causes the protein
  to uncoil
• HCl activates pepsinogen to pepsin which cleaves
  peptide bonds
• Protein is broken down to polypeptides

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Digestion of Protein, Continued

• Small Intestine
• Pancreas and small intestine secrete proteases
  that break polypeptides down into tri- and
  di-peptides and amino acids
• Villi secrete peptidases that break all peptides
  down into amino acids for absorption
• Absorption Single amino acids transported
  across intestinal wall, carried to liver

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Essential Amino Acids (EAA)

• 20 AA
• 11 non-essential
• 9 essential
• Histadine
• Isoleucine
• Leucine
• Lysine

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Essential Amino Acids, Cont

• EAAs, continued
• Methionine
• Phenylalanine
• Threonine
• Tryptophan
• Valine
• 9 essential amino acids must be obtained from
  foods

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Table 6-1 (2)Page 182
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Functions of Protein

• Primary function building and rebuilding
• Also used for energy
• Deamination (removal of NH2)
• NH3
• Ammonia/Urea
• 900 kcals to spare protein

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Functions of Protein Cont.

• Enzymes - protein catalysts
• Build or break down compounds
• Unaffected by reaction
• Regulates fluid balance
• Hormones
• Agents made in one place, carried through blood,
  act in another part of the body

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Functions of Protein, Continued

• Transport nutrients
• Lipids, vitamins, minerals, oxygen
• Visual pigments (opsin)
• Blood clotting (fibrin)
• Connective tissue (collagen)
• Buffer acid-base balance of blood
• Antibodies

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Protein in the Diet

• Protein Quality
• Protein Malnutrition
• Dietary Recommendations
• Protein Excess
• Vegetarian Diets

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Protein Quality

• Complete protein
• Contains all 9 EAAs
• High quality protein
• Contains all 9 EAAs in the proportions needed by
  body
• Animal foods contain all essential amino acids
• Plant foods diverse, missing one or more EAA

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Protein Quality

• Reference protein
• Based on EAA requirements of preschool-age
  children
• Standard used to measure the quality of
  proteins biological value scores
• Egg white 1.00
• Milk protein (casein) 1.00
• Soybean .99
• Beef .92
• Whole wheat .40
• Regardless of quality of protein, body uses
  protein for energy if deficient in total kcals

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Protein Deficiency

• Protein-Calorie Malnutrition (PCM)
• Also called Protein-Energy Malnutrition (PEM)
• Marasmus, kwashiorkor, or combination
• Children thin for height, short for age
• Adults alcoholics, hospitalized person

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Protein Deficiency

• Kwashiorkor
• Inadequate protein intake
• May have adequate kcals
• Disease of weaning (typically about age 2)
• Edema, fatty liver
• Body proteins broken down --gt decreased
  antibodies --gt children often die from dysentery
• With adequate nutrition, can restore body

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In-text Figure Page 199
The edema and enlarged liver characteristic of
kwashiorkor are apparent in this childs swollen
belly. Malnourished children com- monly have an
enlarged abdomen from parasites as well.
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Protein Deficiency, Continued

• Marasmus
• Deficiency of kcals, protein, vitamins, minerals
• Skin and bones appearance
• Infancy to 6 - 18 months also adults w/
  extremely poor intake over time
• Impaired brain development
• Child may never catch up

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Protein Recommendations

• Dietary Goals
• 10 - 35 protein
• 45 - 65 CHO
• 20-35 fat
• RDA
• 0.8 g protein/kg IBW (Ideal Body Weight)
• RDA gives generous safety margin
• ? protein for 170

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Nitrogen Balance

• Equilibrium
• Nitrogen in Nitrogen out
• Healthy adults
• Positive nitrogen balance
• Nitrogen in gt Nitrogen out
• Pregnancy, growth

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Nitrogen Balance, Continued

• Negative nitrogen balance
• Nitrogen in lt Nitrogen out
• Immobile
• Illness and infection
• Muscle atrophy
• Wounds
• Fasting

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Protein and Amino Acid Supplements

• Protein powders have not been found to improve
  athletic performance
• Whey protein waste product of cheese
  manufacturing, common in protein powders
• Amino acid supplements may be harmful
• Branched-chain amino acids provide little fuel
• Athletes in training may need 1.2-1.7gm/kg
  healthy weight

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Protein Excess

• Protein overload (consuming too much protein or
  amino acids)
• Kidney/liver hypertrophy
• Promotes calcium excretion (high animal protein
  intake)
• Increased urination --gt dehydration
• Likely consuming less fruits, vegetables, grains
• Stress balance! Avoid gt 2 x RDA

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Highlight Nutritional Genomics

• Examine how nutrition affects genes
• Genomics Study of genes in an organism, their
  interactions with the environment
• Human genome Genetic material in the
  chromosomes of a persons cells
• Phenylketonuria (PKU) A single gene disorder,
  can be affected by nutrition intervention
• www.cdc.gov/genomics