Protein

FOOD SOURCES OF PROTEIN

  • Protein is essential for various bodily functions.

Major Sources of Protein

  • Dairy Products
      - Nonfat Greek yogurt (5.3 oz): 14 g of protein
      - 1% low-fat milk (1 cup): 8 g of protein
      - Cheddar cheese (1 oz): 7 g of protein

  • Fruits
      - Peach (1 medium): 1.4 g of protein
      - Banana (1 medium): 1.3 g of protein

  • Grains
      - Quinoa, cooked (1 cup): 8 g of protein
      - Oatmeal, cooked (1 cup): 6 g of protein
      - Whole wheat bread (1 slice): 3.6 g of protein

  • Vegetables
      - Brussels sprouts (1 cup): 5 g of protein
      - Potato, baked (1 medium): 4 g of protein
      - Corn (1 cup): 5 g of protein

  • Meats
      - Chicken breast, roasted (3 oz): 24 g of protein
      - Tuna, canned (3 oz): 20 g of protein
      - Peanuts (1 oz): 7 g of protein

MYPLATE.gov

  • Source for balance in meals incorporating different food categories to meet protein needs.

AMINO ACID STRUCTURE

  • Amino acids are the building blocks of proteins.

  • Each amino acid has a central carbon, an amine group (NH2), an acid group (COOH), a hydrogen atom and a variable side chain that determines its specific characteristics.
      - Glycine: Simplest amino acid, represented structurally.
      - Leucine: Branched-chain amino acid; essential for muscle repair.
      - Aspartic acid: Non-essential amino acid.

THE ROLE OF AMINO ACIDS

  • Polypeptides: Proteins composed of 10 or more amino acids.
     

Essential Amino Acids (9)

  1. Histidine

  2. Isoleucine*

  3. Leucine*

  4. Lysine

  5. Methionine

  6. Phenylalanine

  7. Threonine

  8. Tryptophan

  9. Valine*
    (*Branched-chain amino acid)

Nonessential Amino Acids (11)

  1. Alanine

  2. Arginine

  3. Asparagine

  4. Aspartic acid

  5. Cysteine

  6. Glutamic acid

  7. Glutamine

  8. Proline

  9. Serine

  10. Tyrosine

  11. Glycine

PROTEIN SYNTHESIS

Transcription:

  • The genetic code from DNA is copied to mRNA inside the nucleus.

  • Process: DNA strand → mRNA strand

Translation:

  1. mRNA moves from the nucleus to ribosomes in the cytoplasm.

  2. tRNA carries amino acids to ribosomes.

  3. Polypeptide chains are assembled based on mRNA coding.

  4. Peptide bonds link amino acids together to form proteins.

PROTEIN SHAPE DETERMINES FUNCTION

  • The final shape of a protein directly impacts its function; for example:
      - The globular shape of hemoglobin leads to the production of red blood cells that are flat discs, facilitating oxygen transport.

DENATURED PROTEINS

  • Denaturation: Alteration of a protein's shape due to:
      - Heat
      - Enzymatic action
      - Acid or alkaline solutions
      - Agitation

  • Results in reduced biological activity of the protein.

ROLES OF PROTEIN IN THE BODY

  1. Cell production, growth, repair, and maintenance

  2. Production of enzymes, hormones, and neurotransmitters

  3. Maintenance of fluid balance

  4. Transportation of nutrients

  5. Acid-base balance

  6. Production of antibodies

  7. Glucose production

  8. Energy source during starvation or intense exercise
       

Edema

  • Can occur due to insufficient protein intake or reduced ability to synthesize protein; affects fluid balance in the body.

PROTEINS IN TRANSPORT

  • Proteins help transport electrolytes across cell membranes, involving interactions with sodium and potassium to maintain cellular homeostasis.

AMINO ACID TURNOVER

  • Old proteins are broken apart to recycle amino acids, which can then be used for:
      - Making new proteins (enzymes, antibodies, etc.)
      - Synthesis of non-protein nitrogen-containing compounds (creatinine, serotonin)
      - Conversion to fats or glucose for energy purposes.
      - Deamination is then used to excrete excess nitrogen in the form of urea.

PROTEIN DIGESTION AND ABSORPTION

  1. Proteins are mechanically broken down in the mouth and mixed with saliva.

  2. In the stomach, hydrochloric acid denatures proteins, and pepsin breaks them down into polypeptides.

  3. Proteases from the pancreas further digest peptides in the small intestine into amino acids.

  4. Amino acids are absorbed and transported to the liver for distribution to the body.

HOW MUCH PROTEIN DO YOU NEED?

PROTEIN AMDR (Acceptable Macronutrient Distribution Range)

  • Protein should contribute 10-35% of total daily calories.

  • For a 2000 calorie diet, this amounts to 50-175 grams of protein intake or 200-700 calories.

RDA (Recommended Dietary Allowance)

  • 0.35 grams per pound or 0.8 grams per kilogram of body weight.
      - Example Calculations:
        - 165 pounds = 165 * 0.35 = 60 grams protein/day
        - 75 kg = 75 * 0.8 = 60 grams protein/day

INDIVIDUAL FACTORS AFFECTING PROTEIN NEEDS

  • Increased needs for:
      - Growth phases (pregnancy, infancy, adolescence)
      - Recovery from injury
      - Athletes

PROTEIN RDA CHART

  • Specific needs in grams per kilogram of body weight based on activity level (e.g., athletes may require up to 2.0 g/kg/day).

PROTEIN BALANCE

  • Positive Protein Balance: Intake surpasses excretion (e.g., during growth or recovery).

  • Equilibrium: Intake meets excretion (e.g., healthy adults).

  • Negative Protein Balance: Excretion exceeds intake (e.g., malnutrition, illness).

ATHLETES AND PROTEIN NEEDS

  • Requirement increases due to:
      - Enhanced oxygen delivery for hemoglobin production
      - Protein catabolism during intense exercise
      - Tissue repair post-injury

GUIDELINES FOR PROTEIN INTAKE

  • Choose lean meats and low-fat dairy to limit saturated fats.

  • Utilize plant sources as they provide additional health benefits.

  • Eat fatty fish for omega-3 fatty acids.

EXCESSIVE PROTEIN CONSUMPTION

  • Can lead to:
      - Increased risk of heart disease and certain cancers.
      - Elevated urinary calcium loss, contributing to osteoporosis.
      - Dehydration due to increased fluid requirements.

PROTEIN-CALORIE MALNUTRITION

  • Insufficient calorie and protein intake can lead to severe body wasting and infection risk, commonly seen in underdeveloped regions and vulnerable populations.

UNDERNUTRITION IN CHILDREN

  • Conditions: Kwashiorkor and Marasmus characterized by different symptoms of protein-energy malnutrition affecting growth and immune function.

VEGETARIAN DIETS

  • Types of Vegetarian Diets:
      1. Semi-vegetarian/Flexitarian
      2. Lacto-ovo vegetarian
      3. Lacto-vegetarian
      4. Ovo-vegetarian
      5. Pesco-vegetarian
      6. Vegan

BENEFITS OF VEGETARIAN DIETS

  • Associated with lower chronic disease risks, including obesity and certain cancers.

NUTRIENTS OF CONCERN IN A VEGAN DIET

  • Vitamin B12: Important for DNA synthesis.

  • Vitamin D: Essential for bone growth.

  • Iron, Calcium, Zinc: Critical for metabolic functions, bone health, and immune system function.

Food Sources for Vegan Nutrients:

  • Fortified cereals, nuts, legumes, and leafy greens to meet nutritional gaps.

REVIEW QUESTIONS

  1. Describe the basic structure of an amino acid.

  2. What is the difference between the essential and nonessential amino acids?

  3. List 3 rich food sources of protein.

  4. During what situations is the body in positive protein balance? Negative protein balance?

  5. What is the RDA for protein for a person weighing 70 kg or 154 lbs?