Protein: Amino Acids
Chapter 6
Amino Acids
 Atoms in All Amino Acids
 Carbon, hydrogen, oxygen + nitrogen
 Amino Acid Structure
 Central Carbon with 4 spaces
1. Hydrogen
2. Amino group
3. Acid group
4. Unique side group or side chain
Amino Acid
Side group
varies
Amino
group
Acid
group
Identical except for Side Group
Glycine
Alanine
Aspartic acid
Phenylalanine
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 Parkinson’s 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.
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.
The Chemist’s 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
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
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.
Condensation Rxn to Dipeptide
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
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.
The Chemist’s View of
Proteins
 Protein
 Denaturation
 Disruption of
stability
 Uncoil and lose
shape
 Stomach acid
 Heat (cooking)
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.
Insulin is Curly
(Sulfur Bonds)
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.
[Animation 0606]
Protein Absorption
 Used by intestinal cells for energy or
synthesis of necessary compounds.
 Amino acids are transported to the liver via
capillaries
Protein Digestion
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
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
Animation 0607
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
Protein Sequencing Error
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
Two of Protein’s 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)
Enzyme Action of Proteins
B
A
A
B
New
compound
A B
Enzyme
The separate compounds,
A and B, are attracted to
the enzyme’s active site,
making a reaction likely.
Enzyme
The enzyme forms a
complex with A and B.
Enzyme
The enzyme is
unchanged, but A and B
have formed a new
compound, AB.
Stepped Art
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
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
Fluid Imbalance
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.
Transporters
 Carry lipids, vitamins, minerals and
oxygen in the body.
 Ex: Heme Fe captured from SI by a
protein then attached to globin. Hemoglobin carries O2 from lungs to cells.
 Act as pumps in cell membranes,
transferring compounds from one side of
the cell membrane to the other.
Transport Proteins
Animation 0610
Antibodies
 Fight antigens- bacteria and viruses
 Provide immunity to fight an antigen
more quickly the second time exposure
occurs
 Immunity: molecular memory
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)
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
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
Nitrogen Balance Determinants
 Positive
 Growing years
 Pregnancy
 Recovery, healing
 Negative
 Burns, injuries
 Diseases, infections
 Starvation or very low-protein diet
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
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
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
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
Transamination and Synthesis
of Nonessential Amino Acid
Side
group
Keto acid A
Side
group
+
Amino acid B
Side
group
Amino acid A
Side
group
+
Keto acid B
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.
Side
group
Side
group
Amino acid
Keto acid
Deamination
of a
Nonessential
Amino Acid
The deamination of an amino acid
produces ammonia (NH3) and a keto acid.
Side
group
Keto acid
Side
group
Amino acid
Given a source of NH3, the body can make
nonessential amino acids from keto acids.
Synthesis
of a
Nonessential
Amino Acid
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
Ammonia
Carbon
dioxide
Ammonia
UREA SYNTHESIS
Water
Urea
Amino acids
Bloodstream
Ammonia (NH3)
+
CO2
Liver
Urea
Urea
Bloodstream
Kidney
Urea
To bladder and
out of body
Converting Ammonia to Urea
 Ammonia and carbon dioxide are combined
in the liver to make urea, body’s principle
vehicle for excreting unused nitrogen
 Liver Dz: High serum NH3
 The kidneys filter urea out of the blood.
 Renal Dz: High serum urea
Protein Quality
 Two factors
 Digestibility
 With other foods consumed
 Animal (90-99%) vs. plant proteins (>90% for
soy and legumes)
 Amino acid composition
 Essential amino acid consumption
 Nitrogen-containing amino groups
 Limiting amino acid thwarts synthesis
Protein Quality
 Reference protein- the protein gold standard
 Preschool-age children’s requirements
 High-quality proteins
 Animal proteins
 Plant proteins
 Complementary proteins
 Low-quality proteins combined to provide
adequate levels of essential amino acids
Ile
Legumes
Grains
Together
Lys
Met
Trp
Complementary Protein
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
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
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
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
Protein-Energy Malnutrition
Protein-Energy Malnutrition
(PEM)
 Infections
 Degradation of antibodies
 Fever.
 Fluid imbalances and dysentery.
 Anemia
 Dysentery
 Heart failure and possible death.
 Rehydration and nutrition intervention
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
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.
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
Recommended Intakes of Protein
 Protein in abundance
 Intake in U.S., Canada and most developed
countries
 Self-inflicted protein deficiencies
 Key diet principle – moderation
Nutritional Genomics
 New field
 Nutrigenomics
 Nutrients influence gene activity
 Nutrigenetics
 Genes influence activity of nutrients
 Human genome
Genomics Primer
1 The human genome is a
Cell
Nucleus
1
complete set of genetic
material organized into 46
chromosomes, located
within the nucleus of a cell.
2 A chromosome is made
2
of DNA and associated
proteins.
Chromosome
3 The double helical
5
3 DNA
Gene
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.
sequence of nucleotide
4 The
bases (C, G, A, T)
4
determines the amino acid
sequence of proteins.
These bases are connected
by hydrogen bonding to
form base pairs—adenine
(A) with thymine (T) and
guanine (G) with cytosine
(C).
5 A gene is a segment of DNA
that includes the information
needed to synthesize one or
more proteins.
Nutritional Genomics
Genes
Food and nutrients
Nutritional
genomics
Nutritional genomics examines the interactions of genes and nutrients. These
interactions include both nutrigenetics and nutrigenomics.
Genes
Nutrigenetics
Nutrient absorption
Nutrient use and metabolism
Nutrient requirements
Food and nutrient tolerances
Nutrigenetics (or nutritional genetics) examines how genes influence the activities
of nutrients.
Gene mutation
Gene expression
Gene programmingaa
Food and nutrients
Nutrigenomics
Nutrigenomics, which includes epigenetics, examines how nutrients influence the
activities of genes.
A Genomics Primer
 DNA
 46 chromosomes
 Nucleotide bases
 Gene expression
 Genetic information to protein synthesis
 Gene presence vs. gene expression
 Epigenetics
 DNA methylation
Nutrients and phytochemicals
1 Nutrients and phytochemicals
1
Substances
generated during
metabolism
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.
Gene expression activated
or silenced
2
Protein synthesis starts
or stops
3
2 Activating or silencing a
gene leads to an increase
or decrease in the synthesis
of specific proteins.
3 These processes ultimately
affect a person’s health.
Disease prevention
or progression
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)
Genetic Variation and Disease
 Multigene disorders
 Study expression and interaction of multiple
genes
 Sensitive to environmental influences
 Example
 Heart disease
 Single nucleotide polymorphisms (SNPs)