CH 6: Proteins and Amino Acids

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CH 6 Proteins and Amino Acids
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Proteins

• Consider last as protein is the bodys least
  desirable source of energy
• 4 kcal/gram
• When body uses protein for energy it is not
  available to perform other critical functions
• No protein stores all protein has a function in
  the body

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Chemical Nature of Proteins

• Proteins are chains of amino acids (a.a.) joined
  by peptide bonds
• Most are 100s of a.a. long
• Order of the a.a. determined by your DNA
• For the protein to function the chain must fold
  up properly

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Amino Acids

• 20 different amino acids
• Each has the same core structure
• Differ in the side group attached
• All contain the elements C, H, O, N
• Carbs and lipids do not contain N
• Cannot make protein from carbs and lipids
• May also contain sulfur

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Amino Acids

• The body can make 11 of the a.a.
• These are the nonessential a.a.
• Essential a.a.
• 9 a.a. that the body either cannot make or cannot
  make in sufficient quantity to meet its needs
• Some a.a. are conditionally essential

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Amino Acids

• Diet must provide all 9 of the essential a.a. on
  a regular/daily basis for proteins to be made
• Need all 20 a.a. to make most proteins

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Amino Acids

• The body regularly breaks down proteins and
  remakes them or uses them for energy as needed
• If an essential a.a. is missing the body cannot
  make all of the proteins it needs
• Hair and nails may grow more slowly
• Immune system compromised (antibodies are
  proteins)

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Protein Intake

• Recommended level of intake is expressed 2 ways
• 10 25 daily caloric intake
• 0.8 grams protein per kg body weight (RDA)
• Computer program uses this value
• Most meet this level EASILY

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Protein Function

• Growth, maintenance, and repair of body tissue
• Need protein to make muscles, skin, hair, blood
  vessels..
• Cannot grow without protein
• Replace lining of GI tract every 3 days
  (maintenance example)

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Protein Function

• Enzymes
• Enzymes are proteins that catalyze (speed up)
  chemical reactions
• Every reaction in the body requires a specific
  enzyme

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Protein Function

• Hormones
• Hormones are chemical messengers
• Travel to target cells/organs and ilicit a
  response
• Examples
• Insulin and glucagon
• Growth hormone
• Thyroxin regulates metabolic rate

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Protein Function

• Antibodies
• Component of immune system
• Attack foreign substances in the body

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Protein Function

• Transportation of Substances
• Proteins are needed to transport lipids in the
  blood
• Proteins are needed to transport substances
  across cell membranes
• Need for nerve and muscle contraction
• Proteins are needed to absorb calcium and iron

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Protein Function

• Fluid Balance
• Proteins attract water
• 3 major fluid compartments each contain
  proteins
• Inside cells
• Plasma in the blood
• Fluid bathing cells (least fluid, least protein)

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Protein Function

• Fluid Balance
• Generally proteins do not leave their
  compartments
• Fluids can move among compartments
• Fluids are drawn to the proteins
• Need enough protein in the blood and inside cells
  to hold water in these compartments and prevent
  edema

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Protein Function

• Edema occurs when there are inadequate plasma
  proteins
• This occurs when
• Liver disease
• Inadequate protein/food intake
• Kidney disease ? blood proteins excreted
• Injury breaks open cells

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Protein Function

• Acid Base Balance
• Proteins can act as acids and bases
• Help keep body fluids at a safe pH
• Serve as buffers in the body

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Protein Function

• Energy
• 4 kcal/gram
• Use as a source of energy when glucose/glycogen
  stores are empty

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Nitrogen Balance

• Positive Nitrogen Balance
• Making more protein than breaking down
• Anabolism gt catabolism
• Pregnant women
• Infants and children
• Athletes (building muscle)
• Recovering from surgery, injury, or illness

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Nitrogen Balance

• Negative Nitrogen Balance
• Breaking down more protein than you are making
• Catabolism gt anabolism
• Illness, fever
• Burn victims
• Starvation/anorexia

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Nitrogen Balance

• In Zero Nitrogen Balance
• Protein made protein broken down
• Anabolism catabolism
• Most adults are in zero nitrogen balance

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Protein in the Diet

• Complete Proteins
• Contain all 9 essential a.a. in adequate amounts
• Food Sources
• Most animal sources of protein are complete
  proteins
• Meat, poultry, fish, eggs, dairy
• Soy products (plant source of complete protein)

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Protein in the Diet

• Incomplete Proteins
• Lack or are low in 1 or more of the essential
  a.a.
• Food Sources
• Most plant sources are incomplete proteins
• Nuts, seeds, legumes, grains
• Gelatin is an incomplete animal protein

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Protein in the Diet

• Complementary Proteins
• Two or more protein sources that together provide
  all 9 of the essential a.a. (pg 175)
• Any combination of at least 2 categories of plant
  proteins will complement each other
• Seeds
• Grains
• Legumes
• Nuts

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Protein in the Diet

• Examples of meals/foods containing complementary
  proteins
• Rice and beans
• ..

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Protein Digestion

• Digestion
• Mouth
• Stomach
• SI

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Protein Absorption

• Amino acids are absorbed into the cells of the SI
  and enter the __________
• Taken to the __________ for processing

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Protein-Energy Malnutrition

• PEM most often affects children
• 500 million children are malnourished
• Live in poverty
• Adults may also be affected
• At greatest risk are
• Those living in poverty
• Elderly living alone
• Addicts
• Those with eating-disorders
• Those with long-term illness

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Protein-Energy Malnutrition

• Most common is Africa, Central America, South
  America, Middle East, SE/E Asia
• Also see in US
• Homeless, inner-city, rural poverty

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PEM

• Two forms of PEM described
• Marasmus
• chronic malnutrition
• Kwashiorkor
• acute PEM

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Marasmus

• Severe malnutrition over a period of time
• Most common in children ages 6-18 months old
• Primary source of food is a watery cereal gruel

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Marasmus

• Child with marasmus looks like a little old person