Protein: Amino Acids

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Protein Amino Acids
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What are proteins?

• Composed of C, H, O, N arranged into AA linked
  in a polypeptide chain.
• Some AA also contain sulfur.
• Cells link AA in diverse sequences forming
  thousands of different proteins.

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AA

• Each contains amine group (NH2), acid group
  (COOH), hydrogen atom and side group attached to
  a central C atom.
• The side group is a unique chemical structure
  that differentiates one AA from another
• Makes proteins more complex than CHO or Lipid
• Protein composed of 20 different amino acids
  (each with own side chain)

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AA Structure
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Amino Acids

• Essential amino acids
• Cannot be produced by our bodies at all or in
  sufficient enough quantities
• Must be obtained from food
• Nonessential amino acids
• Can be made by our bodies
• Process of transferring the amine group from one
  AA to another acid group and side group

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Essential AA

• Histidine
• Isoleucine
• Leucine
• Lysine
• Valine

• Methionine
• Phenylalanine
• Tryptophan
• Threonine

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Nonessential Amino Acids

• Alanine
• Arginine
• Asparagine
• Aspartic acid
• Cysteine
• Glutamic acid
• Conditionally Essential

• Glutamine
• Glycine
• Proline
• Serine
• Tyrosine

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Conditionally Essential AA

• NEAA that become essential in circumstances when
  need exceeds bodys ability to produce them
• Ex pathological states in adults result of
  intestinal metabolic dysfunction
  (phenylketonuria),.

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How are proteins made?

• Condensation reaction joins amino acids
• Dipeptide 2 AA
• Tripeptide 3 AA
• Oligopeptide 4 - 9 AA
• Polypeptide 10 or more AA
• AA sequences within chains vary.

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Condensation of AA
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AA Sequence of Human Insulin
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How Are Proteins Made?

• The structure of each protein is dictated by the
  DNA of a gene.
• Transcription use of the genetic information in
  DNA to make messenger RNA (mRNA).
• Translation conversion of genetic information in
  mRNA to a chain of amino acids to form a protein.

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How Are Proteins Made?
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How Are Proteins Made?

• Virtually every cell possess genes to make
  proteins
• Each type of cell makes only proteins it needs
• i.e. specialized pancreatic cells make insulin
• Diet may influence gene expression which in turn
  influences protein synthesis
• Basis of nutrigenomics

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Complex Protein Shapes

• Polypeptide chains of AA each having unique
  characteristics twist into complex shapes.
• Each AA has a unique chemical character that
  attracts or repels water.
• Result a wide variety of proteins with varied
  functions that are able to be transported
  throughout watery fluids in body

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Protein Functions

• Different shapes of proteins enable them to have
  different roles in body structure and function.
• Some proteins work alone others can combine with
  other polypeptides to form complexes able to
  carry out unique functions.

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Hemoglobin
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Protein Denaturation

• Denaturation
• Proteins uncoil lose their shape when exposed
  to heat, acids, bases, heavy metals, alcohol and
  other damaging substances.
• Proteins are denatured with digestion

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Protein Digestion

• Stomach
• HCL
• Denatures protein strands so enzymes can attack
  peptide bonds
• Converts pepsinogen to pepsin which cleaves
  proteins into smaller polypeptides some amino
  acids

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Protein Digestion

• Digestion of proteins continues in the small
  intestines.
• Pancreatic enzymes called proteases break
  proteins into smaller polypeptides
• Intestinal enzymes called peptidases complete the
  digestion of proteins into single amino acids

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Protein Absorption

• Intestine
• Specific carriers transport amino acids
• Cells in wall of small intestine absorb single
  AA, dipeptides tripeptides.
• Enzymes in cells break dipeptides tripeptides
  into single AA.
• Once inside cells, AA can be used for energy or
  to synthesize needed compounds.
• AA not used are transported to liver where
  portion of AA are taken up used and remaining
  pass through system to other cells.

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Protein Digestion Absorption
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Protein Digestion Absorption

• Myth Busters
• MYTH
• Consuming enzymes in whole form means they will
  be absorbed whole and generate more in the body
• MYTH
• We need to consume predigested proteins (amino
  acids) to better absorb

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Why do we need proteins?

• Cell growth, repair maintenance
• Form the building blocks for most body
  structures.
• Enzymes hormones
• Enzymes
• Bind or break substances can transform one
  substance into another.
• Hormones
• Act as chemical messengers regulating body
  functions.

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Why do we need proteins?

• Fluid Electrolyte Balance
• Attract fluids, and proteins that are in
  bloodstream, in the cells in the spaces
  surrounding the cells work together to keep
  fluids moving across these spaces in proper
  quantities.

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Why do we need proteins?

• Acid-Base Balance
• Act as buffers by attaching to or releasing
  hydrogen ions as conditions change in body.
• Transport carriers
• Some act as transport proteins and move in body
  fluids carrying nutrients other molecules.
• Can also act as pumps picking up compounds on one
  side and releasing them on other side of membrane.

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Why do we need proteins?

• Antibodies
• Giant protein molecules that are critical
  components of immune system.
• Energy source
• Proteins do not have storage form.
• To use protein for energy, nitrogen (or amine)
  group is removed from AA - deamination.

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Why do we need proteins?

• Other Roles
• Blood clotting, vision, wound healing.
• Protein is the major functional structural
  component of all cells of body.

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Protein Metabolism

• Protein Turnover
• Degradation synthesis of protein.
• When proteins degrade, free AA join circulation.
  These AA mix with AA from dietary protein to form
  AA pool within cells and circulating blood.
• Rate of protein degradation amount of protein
  intake can vary, but pattern of AA within pool
  remains fairly constant.

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Protein Metabolism

• Nitrogen Balance
• Amount of N synthesized/consumed compared with
  amount degraded/excreted in a given period of
  time
• Nitrogen equilibrium N in N out
• Positive nitrogen balance N in gt N out
• Negative nitrogen balance N in lt N out

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Protein Metabolism

• To make proteins NEAA
• To make other compounds
• e.g., neurotransmitter, pigments, etc.
• Energy source
• When glucose is limited, gluconeogenesis
• Starvation always results in loss of lean tissue
• To make fat
• Consumed in excess
• Deaminate protein and convert C fragment to fat

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Protein in Foods

• To make protein, cells must have all the AA
  required
• Liver can produce NEAA
• If EAA is missing, body must break down own
  tissue but cant resynthesize
• To prevent protein wasting, need all nine EAA N
  groups energy for synthesis of other NEAA

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Protein Quality

• Digestibility
• Animal proteins 90-99
• Plant proteins 70-90 (soy legumes gt90)

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Protein Quality

• Limiting amino acid
• EAA that is missing or in smallest supply in AA
  pool so is responsible for slowing or halting
  protein synthesis.
• 4 AA tend to be most limiting
• lysine
• methionine
• threonine
• tryptophan

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Protein Quality

• Complete Protein
• Dietary protein containing all EAA in amounts
  adequate to support growth health.
• Animal proteins tend to be complete
• Meat, fish, poultry, cheese, eggs, yogurt, and
  milk
• Gelatin low quality
• Vegetable protein tends to be incomplete offering
  more diverse patterns, limiting in 1 or more EAA
• Legumes soy high quality
• Corn low quality

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Complementary Proteins

• 2 or more proteins whose AA profile complement
  each other so EAAs missing in 1 are supplied by
  the other
• Mutual supplementation strategy
• combine 2 protein foods in meal so each provides
  what AAs the other lacks
• Can be consumed throughout day not required at
  same meal

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Mutual Supplementation
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Mutual Supplementation
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Disorders related to protein intake

• Protein Energy Malnutrition
• Insufficient protein, energy, or both
• Most widespread form of malnutrition.
• Affects all age groups, but children are most
  vulnerable.
• Acute PEM recent severe food deprivation
• Chronic PEM long-term food deprivation

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Marasmus - Chronic

• Reflects severe deprivation, or impaired
  absorption, of energy, protein, vitamins
  minerals over a long period of time.
• Occurs most often in young children in
  overpopulated areas.
• Causes extreme muscle wasting loss of weight.
  Impairs brain development learning ability.
  Reduces synthesis of hormones which slows
  metabolism lowers body temperature. Limited
  digestion absorption of nutrients.

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Kwashiorkor - Acute

• Acute form due to inadequate protein intake or,
  more commonly, from infections (i.e. food
  posisoning).
• Displaced child (18 mts-2 yrs).
• Loss of muscle fat less severe
• but edema fatty liver.
• May co-exist with marasmus

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Protein Energy Malnutrition

• PEM can affect children and adults in all
  countries.
• In Canada
• Those in poverty in inner cities or isolated
  rural areas
• Elderly (living alone)
• Homeless
• People with eating disorders
• Drug or alcohol addiction
• People living with AIDS or cancer

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PEM - Rehabilitation

• Many infants die
• due to infections, fever, electrolytic imbalance,
  anemia
• Need rehydration nutritional supplementation
• Long-term solutions need to address food security
  issues community development strategies

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Disorders related to genetic abnormalities

• Sickle cell anemia
• Causes RBCs to be shaped like a sickle. Get
  clogged in vessels break apart, damaging cells
  causing anemia.
• Phenylketonuria (PKU)
• Does not have the ability to break down
  phenylalanine.
• Cystic fibrosis
• An abnormal protein prevents normal passage of
  chloride in out of certain cells. Causes cells
  to secrete thick, sticky mucus.

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Normal RBC vs sickle RBC
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Health Associations

• Heart Disease
• Correlation between high animal-protein intake
  high blood cholesterol level.
• Research suggest that high blood levels of
  homocysteine may be a risk factor for heart
  disease. Dont know exactly how yet.

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Health Association

• Cancer
• Correlation b/w high animal protein intakes
  risk of some forms of cancer breast, prostate,
  kidneys, pancreas colon.
• Weight Control
• Protein rich foods (often high in fat) can
  contribute to weight gain.
• Can be used to increase satiety in weight
  management strategies.

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Health Association

• Osteoporosis
• Whether excess protein depletes bones of calcium
  may depend on ratio of calcium to protein
  intake.
• Inadequate intake can compromise bone health,
  especially in elderly women teens with AN.

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Health Association

• Kidney Disease
• Excretion of end products of protein metabolism
  depend in part on adequate fluid intake healthy
  kidneys.
• High protein intake increases work of kidneys but
  does not appear to diminish functioning in those
  with normal kidney functioning
• People with kidney problems are advised to eat a
  low protein diet because a high protein diet can
  increase risk of acquiring kidney disease in
  people who are susceptible.

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How much protein should we eat?

• AMDR
• 10 - 35
• RDA
• 19 - gt yrs 0.8 g of protein/kg/day
• For a 132 lb female
• 132 lb ? 2.2 lb/kg 50 kg
• 50 kg X 0.8g/kg 40 g/day
• Higher for infants, growing children, pregnant
  and nursing women, and athletes.
• Adequate energy required to ensure protein not
  used as an energy source!

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How Much Protein Should We Eat?
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Does our diet compare?

• Average daily calorie intake from protein for
  children teens is 14.7 and 16.8 for adults.
• Among children and teens, boys derive a larger
  proportion of their calories from protein than
  girls.

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Does our diet compare?

• Protein intake in N. America high due to
  abundance of food central role of meats
• Single ounce of meat or ½ cup legumes delivers 7
  grams protein
• 8 ounces (2 food guide servings) provides more
  than the RDA for average size person
• Athletes can generally derive adequate protein by
  consuming enough energy for needs with 10-35 of
  energy from protein

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Food Sources

• Meats
• Milk products
• Soy products
• Legumes
• Whole grains
• Nuts

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Supplements

• Developed countries more protein intake than
  needed
• Supplements of protein or AA not needed
• Generally a waste of
• Supplements of single AA can be dangerous
• Concern
• competition for carriers
• creation of a deficiency of another AA
• reaching toxic levels of certain AA
• Adequate dietary consumption provides all the
  variety we need

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Vegetarian Diets

• Vegetarianism restricting the diet to foods of
  plant origin.
• There are many versions of vegetarianism.
• There are many reasons to adopt a vegetarian diet.

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Vegetarian Diets
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Why Vegetarianism?

• People chose vegetarianism for
• Health benefits
• Ecological reasons
• Religious reasons
• Ethical reasons
• Concerns over food safety

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Health Benefits of Vegetarianism

• Lower intake of fat and total energy
• Lower blood pressure
• Reduce the risk of heart disease
• Reduce the risk of some types of cancer
• Fewer digestive problems

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Challenges of Vegetarianism

• Vegetarian diets can be low in some vitamins and
  minerals
• Vitamin B12
• Vitamin D
• Riboflavin
• Iron
• Calcium
• Zinc

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Challenges of a Vegetarian Diet

• Vegetarians must plan a balanced and adequate
  diet.
• Vegetarians should include complementary proteins
  or use soy products as a complete protein
  source.
• Vegetarians should use a Vegetarian Food Guide
  Pyramid to design their diet.

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Vegetarian Food Guide Pyramid
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Next

• Chapter 7
• Metabolism Transformation and Interactions