BMS208 Human Nutrition

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BMS208 Human Nutrition

• Topic 6 Protein Amino acids
• Chris Blanchard

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Learning objectives

• Describe how the chemical structure of proteins
  differs from the structures of carbohydrates and
  fats.
• List the 9 essential amino acids.
• Trace the digestion of protein and list the
  enzymes needed to complete the process.
• Explain the process used by the body to
  synthesize new proteins.
• List the 8 major functions of protein in the
  body.
• Describe nitrogen balance and provide examples of
  positive nitrogen balance, negative nitrogen
  balance, and equilibrium.
• Describe deamination, where it occurs in the
  body, the products produced, and the fate of
  these products.

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Learning objectives

• Discuss the factors used to evaluate protein
  quality.
• Describe the diseases that result from inadequate
  intake of protein and protein-kcalories.
• Discuss the health effects of over-consumption of
  protein.
• Calculate the protein needed daily using the RDA
  for protein.
• Discuss the health risks of protein and amino
  acid supplements.
• Define nutritional genomics and explain its
  potential uses in health care.

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Proteins

• Proteins are made from 20 different amino acids,
  9 of which are essential.
• Each amino acid has an amino group, an acid
  group, a hydrogen atom, and a side group.
• It is the side group that makes each amino acid
  unique.
• The sequence of amino acids in each protein
  determines its unique shape and function.

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Amino acid structure
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Amino acid structure
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Amino Acids

• Have unique side groups that result in
  differences in the size, shape and electrical
  charge of an amino acid
• Nonessential amino acids, also called dispensable
  amino acids, are ones the body can create.
• Nonessential amino acids include alanine,
  arginine, asparagine, aspartic acid, cysteine,
  glutamic acid, glutamine, glycine, proline,
  serine, and tyrosine.

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Amino Acids

• Essential amino acids, also called indispensable
  amino acids, must be supplied by the foods people
  consume.
• Essential amino acids include histidine,
  isoleucine, leucine, lysine, methionine,
  phenyalanine, threonine, tryptophan, and valine.
• Conditionally essential amino acids refer to
  amino acids that are normally nonessential but
  essential under certain conditions.

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Peptides

• Amino acid chains are linked by peptide bonds in
  condensation reactions.
• Dipeptides have two amino acids bonded together.
• Tripeptides have three amino acids bonded
  together.
• Polypeptides have more than two amino acids
  bonded together.
• Amino acid sequences are all different, which
  allows for a wide variety of possible sequences.

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Peptides bonds
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Protein Shapes

• Hydrophilic side groups are attracted to water.
• Hydrophobic side groups repel water.
• Coiled and twisted chains help to provide
  stability.

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Protein Shapes
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Protein Shapes
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Protein Functions

• Some carry and store materials.
• Some provide strength.
• Some require minerals for activation (example
  hemoglobin and the mineral iron).

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Protein denaturation

• Uncoiling of protein that changes its ability to
  function.
• Proteins can be denatured by heat and acid.
• After a certain point, denaturation cannot be
  reversed.

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Digestion and Absorption

• Stomach acid and enzymes facilitate the digestion
  of protein.
• It is first denatured, then broken down to
  polypeptides.
• The small intestine continues to break down
  protein into smaller peptides and amino acids so
  it can be absorbed.

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Digestion

• In the Stomach
• Protein is denatured by hydrochloric acid.
• Pepsinogen (a proenzyme) is converted into its
  active form pepsin in the presence of
  hydrochloric acid.
• Pepsin cleaves proteins into smaller polypeptides.

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Digestion

• In the Small Intestine
• Proteases hydrolyze protein into short peptide
  chains called oligopeptides, which contain four
  to nine amino acids.
• Peptidases split proteins into amino acids.

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Absorption

• Used by intestinal cells for energy or synthesis
  of necessary compounds
• Transported to the liver
• Taking enzyme supplements or consuming
  predigested proteins is unnecessary

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Proteins in the Body

• Proteins are versatile and unique. The synthesis
  of protein is determined by genetic information.
• Protein is constantly being broken down and
  synthesized in the body.
• Researchers measure nitrogen balance to study
  synthesis, degradation and excretion of protein.
• Protein has many important functions in the body.
  
• Protein can be used for energy if needed its
  excesses are stored as fat.
• The study of proteins is called proteomics.

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Protein Synthesis

• Synthesis is unique for each human being and is
  determined by the amino acid sequence.
• Delivering the instructions through messenger RNA
• Carries a code to the nuclear membrane and
  attaches to ribosomes
• Presents a list to make a strand of protein
• Transfer RNA lines up the amino acids and brings
  them to the messenger

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Protein Synthesis

• Sequencing errors can cause altered proteins to
  be made.
• An example is sickle-cell anemia where an
  incorrect amino acid sequence interferes with the
  cells ability to carry oxygen.
• Cells regulate gene expression to make the type
  of protein needed for that cell.
• Epigenetics refers to a nutrients ability to
  activate or silence genes without interfering
  with the genetic sequence.

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Roles of Proteins

• Building Materials for Growth and Maintenance
• A matrix of collagen is filled with minerals to
  provide strength to bones and teeth.
• Replaces tissues including the skin, hair, nails,
  and GI tract lining
• Enzymes are proteins that facilitate anabolic
  (building up) and catabolic (breaking down)
  chemical reactions.
• Hormones regulate body processes and some
  hormones are proteins. An example is insulin.

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Enzymes
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Roles of Proteins

• Regulators of Fluid Balance
• Plasma proteins attract water
• Maintain the volume of body fluids to prevent
  edema which is excessive fluid
• Maintain the composition of body fluids

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Roles of Proteins

• Acid-Base Regulators
• Act as buffers by keeping solutions acidic or
  alkaline
• Acids are compounds that release hydrogen ions in
  a solution.
• Bases are compounds that accept hydrogen ions in
  a solution.
• Acidosis is high levels of acid in the blood and
  body fluids.
• Alkalosis is high levels of alkalinity in the
  blood and body fluids.

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Roles of Proteins

• Transporters
• Carry lipids, vitamins, minerals and oxygen in
  the body
• Act as pumps in cell membranes, transferring
  compounds from one side of the cell membrane to
  the other

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Roles of Proteins

• Antibodies
• Fight antigens, such as bacteria and viruses,
  that invade the body
• Provide immunity to fight an antigen more quickly
  the second time exposure occurs

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Roles of Proteins

• Source of energy and glucose if needed
• Other Roles
• Blood clotting by producing fibrin which forms a
  solid clot
• Vision by creating light-sensitive pigments in
  the retina

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Protein Metabolism

• Protein Turnover and the Amino Acid Pool
• Protein turnover is the continual making and
  breaking down of protein.
• Amino acid pool is the supply of amino acids that
  are available.
• Amino acids from food are called exogenous.
• Amino acids from within the body are called
  endogenous.

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Protein Metabolism

• Nitrogen Balance
• Zero nitrogen balance is nitrogen equilibrium,
  when input equals output.
• Positive nitrogen balance means nitrogen consumed
  is greater than nitrogen excreted.
• Negative nitrogen balance means nitrogen excreted
  is greater than nitrogen consumed.

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Protein Metabolism

• Using Amino Acids to Make Proteins or
  Nonessential Amino Acids
• Cells can assemble amino acids into the protein
  needed.
• Using Amino Acids to Make Other Compounds
• Neurotransmitters are made from the amino acid
  tyrosine.
• Tyrosine can be made into the melanin pigment or
  thyroxine.
• Tryptophan makes niacin and serotonin.
• Using Amino Acids for Energy and Glucose
• There is no readily available storage form of
  protein.
• Breaks down tissue protein for energy if needed

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Protein Metabolism

• Deaminating Amino Acids
• Nitrogen-containing amino groups are removed.
• Ammonia is released into the bloodstream.
• Ammonia is converted into urea by the liver.
• Kidneys filter urea out of the blood.
• Using Amino Acids to Make Fat
• Excess protein is deaminated and converted into
  fat.
• Nitrogen is excreted.

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Protein in Foods

• Eating foods of high-quality protein is the best
  assurance to get all the essential amino acids.
• Complementary proteins can also supply all the
  essential amino acids.
• A diet inadequate in any of the essential amino
  acids limits protein synthesis.
• The quality of protein is measured by its amino
  acid content, digestibility, and ability to
  support growth.

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Protein Quality

• Digestibility
• Depends on proteins food source
• Animal proteins are 90-99 absorbed.
• Plant proteins are 70-90 absorbed.
• Soy and legumes are 90 absorbed.
• Other foods consumed at the same time can change
  the digestibility

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Protein Quality

• Amino Acid Composition
• The liver can produce nonessential amino acids.
• Cells must dismantle to produce essential amino
  acids if they are not provided in the diet.
• Limiting amino acids are those essential amino
  acids that are supplied in less than the amount
  needed to support protein synthesis.
• Reference Protein is the standard by which other
  proteins are measured.
• Based on their needs for growth and development,
  preschool children are used to establish this
  standard.

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Protein Quality

• High-Quality Proteins
• Contains all the essential amino acids
• Animal foods contain all the essential amino
  acids.
• Plant foods are diverse in content and tend to be
  missing one or more essential amino acids.
• Complementary Proteins
• Combining plant foods that together contain all
  the essential amino acids
• Used by vegetarians

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Protein Quality
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Protein Quality

• A Measure of Protein Quality - PDCAAS (protein
  digestibility-corrected amino acid score)
• Compares amino acid composition of a protein to
  human amino acid requirements
• Adjusts for digestibility

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Protein in Foods

• Protein Regulation for Food Labels
• List protein quantity in grams
• Daily Values is not required but reflects
  quantity and quality of protein using PDCAAS.

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Health Effects and Recommended Intakes of Protein

• Protein deficiency and excesses can be harmful to
  health.
• Protein deficiencies arise from protein-deficient
  diets and energy-deficient diets.
• This is a worldwide malnutrition problem,
  especially for young children.
• High-protein diets have been implicated in
  several chronic diseases.

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Health Effects and Recommended Intakes of Protein

• Protein-Energy Malnutrition (PEM) also called
  protein-kcalorie malnutrition (PCM)
• Classifying PEM
• Chronic PEM and acute PEM
• Maramus, kwashiorkor, or a combination of the two

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Protein-Energy Malnutrition

• Marasmus
• Infancy, 6 to 18 months of age
• Severe deprivation or impaired absorption of
  protein, energy, vitamins and minerals
• Develops slowly
• Severe weight loss and muscle wasting, including
  the heart
• lt 60 weight-for-age
• Anxiety and apathy
• Good appetite is possible
• Hair and skin problems

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Protein-Energy Malnutrition

• Kwashiorkor
• Older infants and young children, 18 months to 2
  years of age
• Inadequate protein intake, infections
• Rapid onset
• Some muscle wasting, some fat retention
• Growth is 60-80 weight-for-age
• Edema and fatty liver
• Apathy, misery, irritability and sadness
• Loss of appetite
• Hair and skin problems

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Protein-Energy Malnutrition

• Marasmus-Kwashiorkor Mix
• Both malnutrition and infections
• Edema of kwashiorkor
• Wasting of marasmus

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Protein-Energy Malnutrition

• Infections
• Lack of antibodies to fight infections
• Fever
• Fluid imbalances and dysentery
• Anemia
• Heart failure and possible death
• Rehabilitation
• Nutrition intervention must be cautious, slowly
  increasing protein.
• Programs involving local people work better.

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Health Effects of Protein

• Heart Disease
• Foods high in animal protein also tend to be high
  in saturated fat.
• Homocysteine levels increase cardiac risks.
• Arginine may protect against cardiac risks.

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Health Effects of Protein

• Cancer
• A high intake of animal protein is associated
  with some cancers.
• Is the problem high protein intake or high fat
  intake?
• Adult Bone Loss (Osteoporosis)
• High protein intake associated with increased
  calcium excretion.
• Inadequate protein intake affects bone health
  also.

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Health Effects of Protein

• Weight Control
• High-protein foods are often high-fat foods.
• Protein at each meal provides satiety.
• Adequate protein, moderate fat and sufficient
  carbohydrate better support weight loss.
• Kidney Disease
• High protein intake increases the work of the
  kidneys.
• Does not seem to cause kidney disease

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Recommended Intakes of Protein

• 10-35 energy intake
• Protein RDA
• 0.8 g/kg/day
• Assumptions
• People are healthy.
• Protein is mixed quality.
• The body will use protein efficiently.

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Recommended Intakes of Protein

• Adequate Energy
• Must consider energy intake
• Must consider total grams of protein
• Protein in abundance is common in first world
  countries

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Protein and Amino Acid Supplements

• Many reasons for supplements
• Protein Powders have not been found to improve
  athletic performance.
• Whey protein is a waste product of cheese
  manufacturing.
• Purified protein preparations increase the work
  of the kidneys.

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Protein and Amino Acid Supplements

• Amino Acid Supplements are not beneficial and can
  be harmful.
• Branched-chain amino acids provide little fuel
  and can be toxic to the brain.
• Lysine appears safe in certain doses.
• Tryptophan has been used experimentally for sleep
  and pain, but may result in a rare blood disorder.

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Nutritional Genomics
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Nutritional Genomics

• In the future, genomics labs may be used to
  analyze an individuals genes to determine what
  diseases the individual may be at risk for
  developing.
• Nutritional genomics involves using a
  multidisciplinary approach to examine how
  nutrition affects genes in the human genome.

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A Genomics Primer

• Human DNA contains 46 chromosomes made up of a
  sequence of nucleotide bases.
• Microarray technology is used to analyze gene
  expression.
• Nutrients are involved in activating or
  suppressing genes without altering the gene
  itself.
• Epigenetics is the study of how the environment
  affects gene expression.
• The benefits of activating or suppressing a
  particular gene are dependent upon the genes
  role.

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A Genomics Primer
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Genetic Variation and Disease

• Small differences in individual genomes
• May affect ability to respond to dietary
  modifications
• Nutritional genomics would allow for
  personalization of recommendations.
• Single-Gene Disorders
• Mutations cause alterations in single genes.
• Phenylketonuria is a single-gene disorder that
  can be affected by nutritional intervention.

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Genetic Variation and Disease

• Multigene Disorders
• Multiple genes are responsible for the disease.
• Heart disease is a multigene disorder that is
  also influenced by environmental factors.
• Genomic research may be helpful in guiding
  treatment choices.
• Variations called single nucleotide polymorphisms
  (SNPs) may influence an individuals ability to
  respond to dietary therapy.

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Clinical Concerns

• An increased understanding of the human genome
  may impact health care by
• Increasing knowledge of individual disease risks
• Individualizing treatment
• Individualizing medications
• Increasing knowledge of nongenetic causes of
  disease
• Some question the benefit of identifying
  individual genetic markers.
• Even if specific recommendation can be made based
  on genes, some may choose not to follow
  recommendations.