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Proteins & Amino Acids
Chapter 6
Where do we
get it?

Animal foods
– Also provide B vitamins and minerals such
as iron, zinc and calcium

Plant foods
– Also provide B vitamins, iron, zinc, fiber
and calcium, but in less absorbable forms

Differences in fiber and fat content
Protein’s Building Blocks:
Amino Acids
Variety in Amino Acid
Structure
Chemist’s View of Proteins

More complex than
carbohydrates or fats
 Twenty amino acids
 Different
characteristics
 9 essential amino
acids
 The rest are either
nonessential or
conditionally
essential
Chemist’s View of Proteins

Peptide bonds link amino acids
 Condensation reactions
 Multiple amino acids linked together: polypeptide
 Protein: one or more polypeptide chains

Amino acid sequencing and protein structure
 Primary structure – chemical bonds
 Secondary structure – electrical attractions
 Tertiary structure – hydrophilic & hydrophobic
 Quaternary structure – two or more polypeptides
Primary Structure: Amino
Acid Sequence
Secondary Structure: Alpha
Helix and Beta Sheet
Tertiary and Quaternary
Structure
Primary through quaternary structure
Tertiary Structure
Protein Shape and
Function

Denaturation
 Disruption of
stability
 Uncoil and lose
shape
 Occurs with
exposure to acid or
high heat

Mutations:
deviations in
primary structure
Mutations: Sickle Cell Anemia
If structure is altered, shape and function may be affected
Protein
Digestion &
Absorption
Use of Amino Acids in Body
Protein Synthesis


Basis of uniqueness of each person
DNA is the template
 Holds the code for amino acid sequences
 Structural proteins give us our shape
 Enzymes give us our metabolism



Protein synthesis happens in every cell
Diet can influence gene expression
Sequencing errors can affect function
DNA Transcription
& Translation into
Protein
Sequencing Errors: Point Mutation
Roles of Proteins

Growth and maintenance
 Building blocks for most body structures
 Collagen
 Replacement of dead or damaged cells

Enzymes
 Assist in break down, build up, and
transform substances
 Catalysts: speed up chemical reactions
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
Fig. 6-9, p. 181
Roles of Proteins

Hormones
 Messenger molecules
 Transported in blood to target tissues
 Regulators of fluid balance
 Hold fluid in the blood
 Without these proteins:
edema
 Acid-base regulators
 Function as buffers

Transporters – specificity
Insulin: A Protein Hormone
Protein Transporter:
The Sodium-Potassium Pump
Roles of Proteins

Antibodies
 Defend body against
disease

Energy and glucose
 Alternative glucose
source during
starvation and
insufficient
carbohydrate intake

Movement: contractile
proteins in muscle
Energy from
Protein
Protein Metabolism

Protein turnover & amino acid pool
 Continual production and destruction
 Need dietary protein to maintain supply
 If needed for energy and glucose
 Wasting of lean body tissue
 Can lower BMR
 Extreme deprivation: organ proteins
compromised
 Prevented by adequate intake of calories,
carbohydrates, and fats
Protein Metabolism

Making proteins & nonessential amino
acids
 If essential amino acid needed, body
breaks down its own proteins
 Rate of protein synthesis may be
compromised
 Limiting amino acid
 Nonessentials can be synthesized

Making other compounds
 Neurotransmitters, hormones
 Melanin
Nonessential Amino Acid
Synthesis

When a nonessential amino acid is not
available from the diet, it can be made in the
body by the process of transamination.
Protein Metabolism

Making fat
 Energy and protein exceed needs
 Carbohydrate intake is adequate
 Can contribute to weight gain
 Creates nitrogenous waste

Nitrogenous waste
 In liver – ammonia converted to urea
 Filtered out of blood and excreted in
urine by kidneys
Nitrogenous Waste: Urea
 Protein intake and
urea production
 Production
increases in
proportion to
dietary protein
 Water
consumption
important in high
protein diets

Two factors
 Digestibility
Protein Quality
 Animal proteins
 Plant proteins
 Amino acid composition
 Essential amino acid consumption
 Nitrogen-containing amino groups
 Limiting amino acid
Health Effects of Protein

High-protein diets
 Heart disease
 Increase risk correlated with high animalprotein intake
 Differences among protein selections
 Cancer
 Certain protein-rich foods, not protein
content of diet, influence risk
 Individuals with kidney disease
 Acceleration of kidney deterioration
Health Effects of Protein

High-protein diets
 Osteoporosis
 Calcium excretion increases
 High animal protein intake more closely
correlated with bone mineral loss
 Ideal amount has not been determined,
and there are multiple influences on bone
health
 Weight control
 Satiation and satiety
Recommended
Intakes of Protein
 Intake in U.S. and Canada typically
adequate or more than adequate
 Dietary sources
 Serving sizes: what we get vs. what we
need
 What is a standard serving size of meat?
 Key diet principle – moderation
 Leave room on the plate for other good stuff!
Protein and Amino Acid
Supplements

Protein powders
 Muscle work vs. protein supplements
 Athletic performance
 Whey protein
 Impact on kidneys?

Amino acid supplements
 Potential risks associated with intake
 Lysine & tryptophan