Protein: Amino Acids

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Protein Amino Acids

• Chapter 6

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Amino Acids

• Atoms in All Amino Acids
• Carbon, hydrogen, oxygen nitrogen
• Amino Acid Structure
• Central Carbon with 4 spaces
• Hydrogen
• Amino group
• Acid group
• Unique side group or side chain

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Amino Acid

Side group varies
Amino group
Acid group
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Identical except for Side Group
Glycine
Alanine
Aspartic acid
Phenylalanine
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The Essential Amino Acids
Isoleucine (Ile) - for muscle production,
maintenance and recovery after workout. Involved
in hemoglobin formation, blood sugar levels,
blood clot formation and energy. Leucine (Leu) -
growth hormone production, tissue production and
repair, prevents muscle wasting, used in treating
conditions such as Parkinsons disease. Lysine
(Lys) - calcium absorption, bone development,
nitrogen maintenance, tissue repair, hormone
production, antibody production. Methionine (Met)
- fat emulsification, digestion, antioxidant
(cancer prevention), arterial plaque prevention
(heart health), and heavy metal removal.
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The Essential Amino Acids

• Phenylalanine (Phe) - tyrosine synthesis and the
  neurochemicals dopamine and norepinephrine.
  Supports learning and memory, brain processes and
  mood elevation.
• Threonine (Thr) monitors bodily proteins for
  maintaining or recycling processes.
• Tryptophan (Trp) - niacin production, serotonin
  production, pain management, sleep and mood
  regulation.
• Valine (Val) helps muscle production, recovery,
  energy, endurance balances nitrogen levels used
  in treatment of alcohol related brain damage.
• Histidine (His) - the 'growth amino' essential
  for young children. Lack of histidine is
  associated with impaired speech and growth.
  Abundant in spirulina, seaweed, sesame, soy, rice
  and legumes.

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The Chemists View of Proteins

• More complex than starches- a glucose chain
• Or fats- carbon chains attached to glycerol
• Twenty amino acids like an alphabet
• Different characteristics
• Essential amino acids- must come from food
• Nonessential amino acids- body can make
• Conditionally essential- When body cannot make
  nonessential, then it has to be in diet. Ex
  phenylketonuria

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Protein Made from Amino Acids

• Proteins (like words)
• Peptide bonds link amino acids (the letters)
• Condensation reactions
• Amino acid sequencing
• Primary structure chemical bonds
• Secondary structure electrical attractions
• Tertiary structure hydrophilic hydrophobic
• Quaternary structure two or more polypeptides

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Amino Acid Chains

• Amino acid chains are linked by peptide bonds in
  condensation reactions.
• a. Dipeptides have two amino acids bonded
  together.
• b. Tripeptides have three amino acids bonded
  together.
• c. Polypeptides have more than two amino acids
  bonded together.

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Condensation Rxn to Dipeptide
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Four Levels of Structure

• Primary structure amino acid sequence
• Secondary structure weak electrical attractions
  within a polypeptide chain (shape)
• The shape of a protein provides stability.
• Tertiary structure polypeptide tangles
• Hydrophilic and hydrophobic side groups
• attraction and repulsion

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Four Levels of Structure

• Quaternary Structures
• Multiple polypeptide interactions
• Some polypeptides function independently.
• Some polypeptides need to combine with other
  polypeptides to function correctly.
• An example of a quaternary structure is
  hemoglobin, which is composed of 4 polypeptide
  chains.

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The Chemists View of Proteins

• Protein
• Denaturation
• Disruption of stability
• Uncoil and lose shape
• Stomach acid
• Heat (cooking)

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Four highly folded polypeptide chains form the
globular hemoglobin protein.

Iron
Heme, the nonprotein portion of hemoglobin, holds
iron.
The amino acid sequence determines the shape of
the polypeptide chain.
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Insulin is Curly
(Sulfur Bonds)
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Protein Digestion

• Mouth chews it up
• Stomach
• Hydrochloric acid denatures proteins
• Pepsinogen converted to pepsin by HCl
• Small intestine
• Hydrolysis 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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Protein Absorption
Animation 0606

• Used by intestinal cells for energy or synthesis
  of necessary compounds.
• Amino acids are transported to the liver via
  capillaries

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Protein Digestion
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Protein Absorption

• Transport into intestinal cells
• Uses of amino acids by intestinal cells
• Unused amino acids transported to liver
• Enzyme pepsin is digested in higher pH of SI
• Predigested proteins unbeneficial for healthy
  people

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Protein Synthesis

• Protein is constantly being broken down and
  synthesized in the body by unique genetic
  information of each person
• Amino acid sequences of proteins
• genes in DNA in cell nuclei
• Diet
• Adequate protein
• Essential amino acids

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Animation 0607
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Protein Synthesis

• DNA template to make mRNA
• Transcription
• mRNA carries code to ribosome
• Ribosomes are protein factories
• mRNA specifies sequence of amino acids
• Translation
• tRNA
• Sequencing errors

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Protein Sequencing Error
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Protein Synthesis

• Gene expression and protein synthesis
• Capability of body cells
• Protein needs met by cell-regulated gene
  expression
• Dietary influence on gene expression
• PUFA influences gene expression for lipases,
  hence development of CHD

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Two of Proteins Roles

• Growth and maintenance
• Building blocks for most body structures
• Collagen matrix for bones
• Replacement of dead or damaged cells
• Enzymes catalyze
• Breakdown rxns (catabolism)
• Building up rxns (anabolism)

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Enzyme Action of Proteins
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The separate compounds, A and B, are attracted to
the enzymes active site, making a reaction
likely.
The enzyme forms a complex with A and B.
The enzyme is unchanged, but A and B have formed
a new compound, AB.
Stepped Art
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Roles of Proteins

• Hormones regulate processes
• Messenger molecules
• Transported in blood to target tissues
• Regulators of fluid balance
• Edema- classic imbalance
• Acid-base regulators
• Attract hydrogen ions
• Transporters specificity

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Regulators of Fluid Balance

• Plasma proteins can leak out of the blood into
  the tissues and attract water, causing swelling
  (edema).
• In critical illness and inflammation
• Inadequate protein synthesis caused by liver
  disease
• Inadequate dietary protein intake

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Fluid Imbalance
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Acid-Base Regulators

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

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Transporters

• Carry lipids, vitamins, minerals and oxygen in
  the body.
• Ex Heme Fe captured from SI by a protein then
  attached to globin. Hemo- globin carries O2 from
  lungs to cells.
• Act as pumps in cell membranes, transferring
  compounds from one side of the cell membrane to
  the other.

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Transport Proteins
Animation 0610
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Antibodies

• Fight antigens- bacteria and viruses
• Provide immunity to fight an antigen more quickly
  the second time exposure occurs
• Immunity molecular memory

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Other Roles of Protein

• Source of energy and glucose in starvation or
  insufficient carbohydrate intake
  (gluconeogenesis)
• Blood clotting by producing fibrin, which forms a
  solid clot.
• Vision by creating light-sensitive pigments in
  the retina (opsin)

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Preview of Protein Metabolism

• Protein turnover amino acid pool
• Continual production and destruction
• Amino acid pool pattern is fairly constant
• Used for protein production
• Used for energy if stripped of nitrogen,
  degrades/converts to glucose or stored as TG
  

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Nitrogen Balance

• Zero Nitrogen Balance synthesis
  degradation
• Positive and negative nitrogen balance
• Amino acids from food are called exogenous-
  protein ingested
• Amino acids from within the body are called
  endogenous- protein

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Nitrogen Balance Determinants

• Positive
• Growing years
• Pregnancy
• Recovery, healing
• Negative
• Burns, injuries
• Diseases, infections
• Starvation or very low-protein diet

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Preview of Protein Metabolism

• Making other compounds from amino acids
• Neurotransmitters (epi- and norepi-), melanin
  pigment and thyroxine are made from tyrosine.
• Niacin and serotonin made from tryptophan.
• Energy from glucose and fatty acids preferred
• Body has no protein storage like adipose or
  glycogen
• Inadequate dietary protein- wasting of lean body
  tissue

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Preview of Protein Metabolism

• Fat production from excess protein
• Energy and protein exceed needs
• Carbohydrate intake is adequate
• Can contribute to weight gain
• Deaminating amino acids
• Stripped of nitrogen-containing amino group
• Ammonia
• Keto acid

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Amino Acids for Energy and Fat

• Muscle and organ protein available for energy if
  needed
• Amino acids whittled down to glucose, nitrogen
  exits in urine.
• Excess calories in protein form are deaminated
  (nitrogen excreted) and converted into fat

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Preview of Protein Metabolism

• Make proteins nonessential amino acids from
  dietary protein
• Breakdown of body protein to obtain essential
  amino acid not in diet
• Keto-acid N needed for nonessentials
• Liver cells and nonessential amino acids
• Converting ammonia to urea
• Liver ammonia and carbon dioxide
• Dietary protein

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Transamination and Synthesis of Nonessential
Amino Acid
Side group
Side group
Side group
Side group
Keto acid B
Keto acid A
Amino acid B
Amino acid A


The body can transfer amino groups (NH2) from an
amino acid to a keto acid, forming a new
nonessential amino acid and a new keto acid.
Transamination reactions require the vitamin B6
coenzyme.
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Side group
Side group
Deamination of a Nonessential Amino Acid
Amino acid
Keto acid
The deamination of an amino acid produces ammonia
(NH3) and a keto acid.
Side group
Side group
Synthesis of a Nonessential Amino Acid
Amino acid
Keto acid
Given a source of NH3, the body can
make nonessential amino acids from keto acids.
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Ammonia (NH3)

• Byproduct of deamination from protein metabolism
• In the liver 2NH3 CO2 H2O urea
• Liver releases urea into blood
• Kidneys filter urea out of blood
• Protein intake, Urea production
• Water consumption needed to avoid
  dehydration

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Ammonia
Ammonia
Carbon dioxide
UREA SYNTHESIS
Water
Urea
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Amino acids
Bloodstream
Ammonia (NH3) CO2
Liver
Urea
Urea
Bloodstream
Kidney
Urea
To bladder and out of body
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Converting Ammonia to Urea

• Ammonia and carbon dioxide are combined in the
  liver to make urea, bodys principle vehicle for
  excreting unused nitrogen
• Liver Dz High serum NH3
• The kidneys filter urea out of the blood.
• Renal Dz High serum urea

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Protein Quality

• Two factors
• Digestibility
• With other foods consumed
• Animal (90-99) vs. plant proteins (gt90 for soy
  and legumes)
• Amino acid composition
• Essential amino acid consumption
• Nitrogen-containing amino groups
• Limiting amino acid thwarts synthesis

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Protein Quality

• Reference protein- the protein gold standard
• Preschool-age childrens requirements
• High-quality proteins
• Animal proteins
• Plant proteins
• Complementary proteins
• Low-quality proteins combined to provide adequate
  levels of essential amino acids

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Ile
Lys
Met
Trp
Legumes
Grains
Together
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Complementary Protein
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Protein Regulations for Food Labels

• Quantity of protein in grams
• Percent Daily Value
• Not mandatory unless
• Protein claims
• Consumption by children under 4 years old
• Quality of protein also figures into DV

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Protein-Energy Malnutrition (PEM)

• Insufficient intake of protein, energy, or both
• Prevalent form of malnutrition worldwide
• Impact on children
• Poor growth
• Most common sign of malnutrition
• Adult PEM in AIDS, TB, anorexia nervosa
• Conditions leading to PEM- food shortage

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Protein-Energy Malnutrition (PEM)

• Marasmus
• Chronic PEM
• Children 6 to 18 months
• Poverty
• Little old people just skin and bones
• Impaired growth, wasting of muscles, impaired
  brain development, lower body temperature
• Digestion and absorption

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Protein-Energy Malnutrition (PEM)

• Kwashiorkor
• Acute PEM
• Children 18 months to 2 years
• Develops rapidly
• Aflatoxins
• Edema, fatty liver, inflammation, infections,
  skin and hair changes, free-radical iron
• Marasmus-Kwashiorkor mix

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Protein-Energy Malnutrition
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Protein-Energy Malnutrition (PEM)

• Infections
• Degradation of antibodies
• Fever.
• Fluid imbalances and dysentery.
• Anemia
• Dysentery
• Heart failure and possible death.
• Rehydration and nutrition intervention

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Health Effects of Protein

• High-protein diets
• Heart disease
• Animal protein /animal fat intake
• Homocysteine levels
• Cancer
• Animal foods, not protein content of diet
• Acceleration of kidney deterioration

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Health Effects of Protein

• High animal protein diets
• Osteoporosis
• Calcium excretion increases
• Weight control
• Satiety
• Adequate protein, moderate fat, and sufficient
  carbohydrate better support weight loss.

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Recommended Protein Intakes

• Need for dietary protein
• Source of essential amino acids
• Practical source of nitrogen
• 10 to 35 percent of daily energy intake
• RDA
• Adults 0.8 grams / kg of body weight / day
• Athletes 1.2-1.7 g/kg/day
• Elderly 1.0-1.2 g/kg/day unless diabetic
• Pregnant / Lactating 1.1-1.3 g/kg/day

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Recommended Intakes of Protein

• Protein in abundance
• Intake in U.S., Canada and most developed
  countries
• Self-inflicted protein deficiencies
• Key diet principle moderation

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Nutritional Genomics

• New field
• Nutrigenomics
• Nutrients influence gene activity
• Nutrigenetics
• Genes influence activity of nutrients
• Human genome

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Genomics Primer
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The human genome is a complete set of genetic
material organized into 46 chromosomes, located
within the nucleus of a cell.
Cell
Nucleus
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2
A chromosome is made of DNA and associated
proteins.
Chromosome
2
3
The double helical structure of a DNA molecule is
made up of two long chains of nucleotides. Each
nucleotide is composed of a phosphate group, a
5-carbon sugar, and a base.
Gene
5
3
DNA
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The sequence of nucleotide bases (C, G, A, T)
determines the amino acid sequence of proteins.
These bases are connected by hydrogen bonding to
form base pairsadenine (A) with thymine (T) and
guanine (G) with cytosine (C).
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A gene is a segment of DNA that includes the
information needed to synthesize one or more
proteins.
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Nutritional Genomics
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Food and nutrients
Genes
Nutritional genomics
Nutritional genomics examines the interactions of
genes and nutrients. These interactions include
both nutrigenetics and nutrigenomics.
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Nutrient absorption Nutrient use and
metabolism Nutrient requirements Food and
nutrient tolerances
Genes
Nutrigenetics
Nutrigenetics (or nutritional genetics) examines
how genes influence the activities of nutrients.
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Gene mutation Gene expression Gene programmingaa
Food and nutrients
Nutrigenomics
Nutrigenomics, which includes epigenetics,
examines how nutrients influence the activities
of genes.
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A Genomics Primer

• DNA
• 46 chromosomes
• Nucleotide bases
• Gene expression
• Genetic information to protein synthesis
• Gene presence vs. gene expression
• Epigenetics
• DNA methylation

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Nutrients and phytochemicals
Nutrients and phytochemicals can interact
directly with genetic signals that turn genes on
or off, thus activating or silencing
gene expression, or indirectly by way of
substances generated during metabolism.
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1
Substances generated during metabolism
Gene expression activated or silenced
Activating or silencing a gene leads to an
increase or decrease in the synthesis of specific
proteins.
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2
Protein synthesis starts or stops
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3
These processes ultimately affect a persons
health.
Disease prevention or progression
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Genetic Variation and Disease

• Genome variation
• About 0.1 percent
• Goal of nutritional genomics
• Customize recommendations that fit individual
  needs
• Single-gene disorders
• Phenylketonuria (PKU)

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Genetic Variation and Disease

• Multigene disorders
• Study expression and interaction of multiple
  genes
• Sensitive to environmental influences
• Example
• Heart disease
• Single nucleotide polymorphisms (SNPs)