Protein

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Protein
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Sources of protein

• Animal muscle products
• Steaks
• Chicken
• Fish
• Shellfish
• Legumes
• Eggs
• Dairy products
• Grains
• Vegetables

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A few functions of proteins

• Major component, but not only one, of muscle
• Enzymes
• Nerve (some) function
• Hormone (some)
• Blood clotting
• Plasma components

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Chemical composition

• Carbon
• Hydrogen
• Oxygen
• Nitrogen

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Amino acids

• Building block of proteins
• 20 different types
• All have same basic construction, except for one
  region (side group), of which there are 20
  variations

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Nonessential amino acids

• Amino acids the body can synthesize
• About 1/2 of total

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Essential amino acids

• Body cannot synthesize at all or not enough
• Must be present in diet
• 9 amino acids

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Conditionally essential amino acids

• Amino acids that normally are not essential, but
  special circumstances increase needs
• Needs then must be met through the diet

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Peptide bonds

• Amino acids join chemically together through
  peptide bonds
• Dipeptide
• 2 amino acids
• Tripeptide
• 3 amino acids
• Polypeptide
• Many amino acids

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Proteins

• Composed polypeptide chains, often containing
  thousands of amino acids
• Precise sequence of amino acids determines the
  specific protein
• DNA codes for the sequence
• Polypeptide chain must twist and fold into a
  specific shape to become functional
• Side groups form bonds with one another
• Sometimes more than one twisted-folded chain is
  necessary to produce the functional protein
• Hemoglobin of blood has 4 chains

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Denaturation

• Bonds between side groups break
• Heat
• Acids
• Etc.
• Protein uncoils and becomes nonfunctional
• Cannot refold
• Did you denature proteins for breakfast today?

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Protein digestion

• Stomach
• HCL uncoils chains
• Pepsin breaks chain into smaller polypeptides
• Small intestine
• Proteases from pancreas and small intestine break
  chains even smaller
• Peptidase on surface of intestinal cells breaks
  remaining peptide bonds and liberates individual
  amino acids, which are then absorbed

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Protein absorption

• Carriers bring amino acids, di- and tri-peptides
  into intestinal cells
• Cells use some amino acids for their own
  metabolism
• Remaining amount is sent to liver

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Useless digestive aids

• Enzyme supplement
• Are digested because they are protein
• Predigested protein
• Absorption works better at the slower rate
  determined by digestion of proteins in tract

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Proteins in the body

• 30,000 different proteins
• 3000 have been studied

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Protein synthesis

• DNA dictates sequences of amino acids through a
  codes embedded in the DNA moleculegenes
• The unique sequence of amino acids determines the
  protein
• If there is a mistake in the code or in the
  translation of the code into protein, the protein
  may not function properly, if at all.
• May result in disease or a fatal condition
• Sickle cell anemia substitution of a single
  incorrect amino acid in two of the four
  polypeptide chains

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Nutrients and gene expression

• Diet has a major effect on which genes code at
  any particular time, the rate at which they code
  and on translation into protein

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Roles of proteins

• Growth and maintenance
• Integral component of most body structures
• Enzymes
• Hormones
• Fluid balance
• Acid-base balance
• Transportation
• Antibodies
• Energy and glucose

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Protein turnover and amino acid pool

• Protein turnover proteins are constantly made
  and then broken down
• Amino acid pool the amino acids present in a
  cell available to draw from to make new proteins
  or for energy or new glucose
• Amino acids from food
• Amino acids from protein turnover
• Proportions within a cell remains fairly constant

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Nitrogen balance

• Zero balance healthy adult
• Protein synthesisdegradation
• Protein intakeloss through urine, sweat, feces

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• Positive balance infants, children, adolescents,
  pregnant women, recovery from protein deficiency
  or illness
• Body synthesizes more protein than it degrades
• Nitrogen intake exceeds nitrogen loss

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• Negative balance starvation, burn, injury,
  infection, fever
• Body degrades more protein than it synthesizes
• Nitrogen output excees intake
• Body looses nitrogen by burning muscle and other
  proteins for energy

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Uses of amino acids

• Protein synthesis
• Manufacture of nonessential amino acids
• Manufacture of other compounds
• Neurotransmitters
• Direct fuel for energy
• Manufacture of new glucose, which is used for
  energy

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Deamination

• Removal of nitrogen from amino acids when they
  are broken down for fuel or glucose
• Produces toxic ammonia
• Liver converts ammonia to less toxic urea
• Kidneys filter urea into urine and it is excreted

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Protein quality

• High quality
• Provides enough essential amino acids for growth
  and maintenance
• Low quality
• Does not provide sufficient amount of essential
  amino acids

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Factors that determine protein quality

• Digestibility
• Animal 90-99
• Plant 70-90
• Soy and legumes-over 90
• Limiting amino acids
• Essential amino acid found in short supply

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Reference protein

• Protein composition of eggs is considered ideal
  to support a young childs growth and development
  and will meet or exceed needs of older children
  and adults
• The egg is the standard against which to measure
  the quality of other proteins

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Complementary proteins

• Two or more dietary proteins whose amino acid
  assortments complement each other in such a way
  that the essential amino acids missing from one
  are supplied by the other
• Important concern for vegetarians who consume no
  animal proteins (vegans)

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PEM

• Protein-energy malnutrition
• Most often strikes young children
• Chronic long term food deprivation
• Short for age
• Acute recent, severe
• Thin for age
• Most prevalent in 3rd world countries, but also
  present in US
• Affects 1/4 children worldwide
• 33,000 children die each day from PEM

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Types of PEM

• Marasmus
• Chronic
• Severe deprivation over long period
• Energy and protein and other nutrient deficiency
• Emaciation
• Kwashiorkor
• Acute
• Some muscle wasting
• Fluid imbalance leads to bloated belly

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Combined marasmus and kwashiorkor

• Can occur in same child
• Can occur to different individuals within the
  same population

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Proteins and health concerns

• High protein intakes possibly linked with
• Heart disease
• Elevated homocysteine linked to heart disease
• Homocysteine rises with increased consumption of
  caffeine, alcohol, tobacco
• Homocysteine levels are inversely related to
  natural B6 and B12 levels, not supplements
• Homocysteine levels are also inversely related to
  arginine levels, naturally occurring or
  supplemental.
• Some cancers
• Osteoporosis
• Kidney disease

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Protein RDA

• .8mg/kg body weight/day
• 10-35 energy intake

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Protein and amino acid supplement

• Not necessary in healthy people
• May be inappropriate for some groups of people
  see p.202
• Do not promote muscle mass or act as significant
  source of energy for athletes

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Possibly useful amino acid supplement

• Lysine may shorten the duration of fever blisters
• not adequate data to support claim
  scientifically at this time
• Tryptophan may promote sleep and ease pain
• Not adequate data to support claim scientifically
  at this time
• No longer commercially available, although
  precursor is

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The end