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Acidic Amino Acids
At neutral pH, lose proton ( --COO− ), negatively charged
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Basic Amino Acids
At neutral pH, gain a proton (-NH3+), positively charged
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Histidine:
contains imidazole group (aromatic ring) that can be positively charged
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Branched
chain protein
essential body can't produce, consumed by muscle
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Essential amino acids
PVT TIM HA*LLAny Help In Learning These Little Molecules Proves Truly Valuable.
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- phenylaline
- threonine
- tryptophan
- valine
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PVT TIM HALL
- phenylalnine
- valine
- threomine
- tryptophan
- Arginine (in some birds)
- Leucine
- Lysine
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¨Primary proteins
¤AAsequence, peptide bonds
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¨Secondary proteins
- hydrogenbonds between backbone atoms
- α-helix or β-sheets
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Tertiary proteins
5 types of bonds between R groups
H bonds
Ionic attraction
Hydrophobic
Hydrophilic
Disulfide bonds
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¨Quaternary:
¨Quaternary: subunit association
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¨Denatured dietary proteins are:
safer (non-functioning enzymes,non-virulent bacteria, viruses)less allergenic¤more digestible, increase exposure toenzymes
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nonessenntal amino acids
- Alanine
- Arginine
- Asparatic acid
- cysteine
- Glutamine
- Glycine
- proline
- serine
- tyrosine
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Essential amino acids
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- phenylaline
- threonine
- tryptophan
- valine
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Peptide Bond Formation
- Covalent bond
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- NH2 reacts w/-COOH
H20 as by-product
- AA side chain determines protein folding
- --> myriad of functions
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All or none
- Histidine deficiency à found in dipeptides in carnosine
- & anserine – very high concentrations in human skeletal muscle & can be degraded to get histidine; degrated Hgb (a histidine-rich protein) may allow body to maintain supply of histidine if deficient in diet.
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¨High quality (complete) protein
- provides 9 Essential AAs in proportion for human
- use
usually from animal sources
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¨Low quality (incomplete) protein
¤EAAs pattern does not match human requirement
¤typically from plant sources
¤one or more EAAs low or missing (e.g. corn low in tryptophan and lysine)
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¨Biological Value (BV)
Ratio of N retained to N absorbed
N retained
N absorbed
- Measures how efficiently the absorbed
- food protein can be turned into body tissue
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¨Protein Efficiency Ratio (PER)
- FDA uses for labeling regulations for
- infant food
- Compares the weight gained in a growing
- rat after 10 days or more eating a standard amount of a specific protein source
(g weight gain/g protein consumed)
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¨Chemical Score
- ¤EAA
- in the food divided by an “ideal” amount for that essential AA
- ¤The
- lowest EAA score is the C.S. for that food
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¨Protein Digestibility Corrected Amino Acid Score
PDCAAS = Chem. Score x digestibility (generally between 0.9-1.0)
Maximum value is 1.0 (= milk, eggs, soy protein)
Nutrition Facts panel rarely lists % DV for protein, since manufacturers don’t calculate PDCAAS
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Net Protein Utilization
(NPU)
Ratio of AA converted to protein to AA supplied
AA converted to protein
AA supplied
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Protein Complementation
Combine foods with different amino acid patterns to supply EAAs in proper proportion
e.g. grain (low in lysine) + bean (low in methionine) = complete protein
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Functions of protein in the body
Energy
5-10% of energy used in body (expensive energy)
Prolonged exercise (↑ 10-15% -- branched chain AA in muscle – Leucine, Isoleucine, Valine)
If there are insufficient total kcalories, then dietary (and body) protein is used for energy
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Functions of protein in the body
¨Glucose formation
- Gluconeogenesis for brain and RBC between meals and low
- CHO diets
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Functions of protein in the body
Acid-base balance
Regulation of pH by buffering resulting from charged amino acid side chains
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Functions of protein in the body
Structure
Connective tissue, bone matrix, epidermal cell walls (skin), lipoproteins, antibodies, etc.
Collagen, actin and myosin, plus hemoglobin make up 50% of the protein in the body
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Functions of protein in the body
Immune function
Antibodies & immune cells require protein
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Functions of protein in the body
Protein hormones and enzymes
Insulin, pituitary hormones, thyroid hormone
Enzymes for thousands of metabolic reactions
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Protein RDA
100 kg x 0.8 g/kg/day = 80 g/day
¨To gain 2 lb (0.91 kg) muscle/week
Muscle is 22% protein.
0.22 x 0.91 kg/wk = 200 g/wk = 29 g/day
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Transamination
Process for synthesizing nonessential amino acids.
Carbon skeleton” from a metabolic cycle accepts amino group to become amino acid
Available for protein synthesis
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Amino Acid “Sparing”
¨Humans do not synthesize cysteine or tyrosine from scratch.
¨Why are they not essential?
Cys is made from Met, and “spares” need for some Met when in the diet.
Tyr is made from Phe.
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¨If transamination did not occur, what
would be the result?
1.Every amino acid would be essential.
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Excess protein (NAS)
- ¨45% kcal from protein – weakness, nausea,
- diarrhea, death (“rabbit starvation”)
- ¨Maximum rate of urea synthesis/excretion
- at 250 g protein/d (approx. 40% kcal)
- ¨High protein does not prevent loss of
- lean tissue during negative energy balance.
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Possible
advantages vegetarian
- ¨Lower rates of some chronic diseases
- (CHD, hypertension, type II diabetes, obesity, some cancers)
- ¨Other lifestyle effects? Absence or
- moderation?
- ¨Benefits of plant sources vs. animal sources
- of proteins
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Possible
disadvantages vegetarian
- ¨Nutrient deficiencies if uninformed –
- B12, Fe, Zn
- ¨Deficiencies and growth retardation in
- children of uninformed vegetarian mothers
- ¨Less nutrient-dense sources of lysine, methionine,
- vitamins B12, D, Ca, Fe, Zn, riboflavin
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