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threonine

  • EAR and RDA for Amino Acids

    Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for amino acids (protein) for healthy adults 19 y and older, mg/kg/day:

    • Estimated Average Requirement (EAR): average, estimated to meet the requirements of 50%.
    • Recommended Dietary Allowance (RDA): average, sufficient to meet the nutrient requirements of nearly all.
    Amino Acids EAR RDA
    phenylalanine + tyrosine 27 33
    valine 19 24
    threonine 16 20
    tryptophan 4 5
    methionine + cysteine 15 19
    leucine 34 42
    isoleucine 15 19
    lysine 31 38
    histidine 11 14
  • Amino Acid Requirements for Adults

    Estimates of Amino Acid Requirements for adultsmg / kg per day

    • Phenylalanine + tyrosine: 14
    • Leucine: 14
    • Methionine + cystine13
    • Histidine: 8–12
    • Lysine: 12
    • Isoleucine: 10
    • Valine: 10
    • Threonine: 7
    • Tryptophan: 3.5

  • All Essential Amino Acids

    An essential amino acid, or indispensable amino acid, is an amino acid that cannot be synthesized by the organism, and must be supplied in diet. 

    The 9 amino acids humans cannot synthesize (F V T W M L I K H):

    • phenylalanine
    • valine
    • threonine
    • tryptophan
    • methionine
    • leucine
    • isoleucine
    • lysine
    • histidine

    Animal and plant proteins are made up of about 20 common amino acids.

    Synthesis of 6 other amino acids - conditionally essential - can be limited under special conditions (R C G Q P Y)arginine, cysteine, glycine, glutamine, proline, and tyrosine.

    Dispensable amino acids can be synthesized in the human body, 5 (A D N E S): alanine, aspartic acid, asparagine, glutamic acid and serine .

John Stuart Mill

A person may cause evil to others not only by his actions but by his inaction, and in either case he is justly accountable to them for the injury.

Protein Structure, Cooked and Denatured Proteins

Proteins are chains of amino acids. The sequence of amino acids in a chain is known as the primary structure of a protein. The chains fold up to form complex three dimensional shapes. The chains can fold on themselves locally (secondary structure) and wrap around themselves to form a specific three dimensional shape (tertiary structure).

The secondary / tertiary structure of a folded protein is directly related to its function. For example, enzymes are proteins that catalyze reactions. They have binding sites that interact with other molecules. These binding sites are created through the folding of the amino acid chains that gives rise to the three dimensional shape of the enzyme.

Denatured Protein

Denaturation of proteins involves the disruption and possible destruction of both the secondary and tertiary structures. Since denaturation reactions are not strong enough to break the peptide bonds, the primary structure (sequence of amino acids) remains the same after a denaturation process. Denaturation disrupts the normal sheets in a protein and uncoils it into a random shape.

Denaturation occurs because the bonding interactions responsible for the secondary structure (hydrogen bonds to amides) and tertiary structure are disrupted. In tertiary structure there are four types of bonding interactions between "side chains" including: hydrogen bonding, salt bridges, disulfide bonds, and non-polar hydrophobic interactions. which may be disrupted. 

Proteins can be denatured through exposure to heat or chemicals. Denatured proteins lose their three dimensional structure and thus their function. 

Digestion of Proteins and Cooking

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there.

Heat disrupts hydrogen bonds and non-polar hydrophobic interactions. This occurs because heat increases the kinetic energy and causes the molecules to vibrate so rapidly and violently that the bonds are disrupted

Foods are cooked to denature the proteins to make it easier for enzymes to digest them. Cooking food denatures some of the proteins in it and makes digestion more efficient. Heating to denature proteins in bacteria and thus destroy the bacteria.

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