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Chapter
6
Proteins and
Amino Acids
#1 Amino Acids Are the Building
Blocks of Protein
• Proteins are sequences
of amino acids
• Types of amino acids
• Indispensable
• Dispensable
• Conditionally
indispensable
#2 Amino Acids Are the
Building Blocks of Proteins
• Amino acids are
identified by their
side groups
Amino Acids Are the
Building Blocks of Proteins
• Protein
Structure:
Unique ThreeDimensional
Shapes and
Functions
• Amino-Acid
Sequence
• Protein Shape
Amino Acids Are the
Building Blocks of Proteins
• Protein Denaturation:
Destabilizing a
Protein’s Shape
Functions of Body Protein
Functions of Body Protein
• Structural and Mechanical Functions
• Enzymes
#3 Essentiality of Amino Acids
• Essential – obtained in diet
• Non essential – body can synthesize
• Conditionally essential – body can
normally synthesize unless under
critical illness
Amino Acids
Peptide chains #4, 5
#6
#7 Functions of Body Proteins
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Hormones
Immune Function
Fluid Balance
Acid–Base Balance
Proteins in the Body
• Protein synthesis
• Directed by cellular
DNA
• Amino acid pool and
protein turnover
• Synthesis of
nonprotein molecules
Proteins in the Body
• Protein and nitrogen excretion
• Deamination of amino acids
• Amino groups converted to urea for excretion
• Nitrogen balance
• Nitrogen intake vs. nitrogen output
Functions of Body Proteins
• Transport Functions
• Sources of Energy and Glucose
Courtesy of the USDA
Proteins Act as Carriers
• Lipoproteins have
embedded proteins
that help them
transport fat and
cholesterol in the
blood.
Denaturation
• Heat, pH, oxidation,
and mechanical
agitation are some
of the forces that
can denature a
protein, causing it to
unfold and lose its
functional shape.
Structural Proteins
• Proteins provide
structure to all cells,
including hair, skin,
nails, and bone. As
part of muscle, they
transform energy
into mechanical
movement.
Hormones
• Hormones are
formed in one part
of the body and
carried in the blood
to a different
location where they
signal cells to alter
activities.
Proteins and the Immune System
• Protein antibodies
are a crucial line of
defense against
invading bacteria
and viruses.
Proteins in the Blood
• Blood proteins
attract fluid into
capillaries.
• This counteracts the
force of the heart
beating, which
pushes fluid out of
capillaries.
#8-10 Protein Digestion and
Absorption
• Stomach
• Proteins are denatured by hydrochloric
acid
• Pepsin begins digestion
• Small intestine
• Pancreatic and intestinal proteases and
peptidases complete digestion
• Amino acids are absorbed into the
bloodstream
Protein Digestion
Protein Digestion and Absorption
• Amino Acid and Peptide Absorption
#11 Deamination
• All proteins are broken into amino acids
• To release energy from the amino acid,
the body removes a nitrogen group
• The carbon skeleton is used for energy
and can be used to make glucose.
• If our diet contains more protein than we
need, it is sored as fat or used as
glucose.
Hormone Actions
#12 Phases of Protein Synthesis
• Uniqueness of each person
• Amino acid sequences of proteins
• Genes – DNA
• Diet
• Adequate protein
• Essential amino acids
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
#13 Protein (Nitrogen) Balance
• A pregnant woman adds protein so she
has a positive nitrogen balance.
• A healthy person who is neither gaining
nor losing nitrogen is in nitrogen
equilibrium.
• A person who is severely ill and losing
protein has a negative nitrogen balance.
#15 Proteins in the Diet
• Recommended protein intake
• Adult RDA = 0.8 grams/kilogram body
weight
• Infant RDA = ~1.5 grams/kilogram body
weight
• Physical stress, burns, wounds = can
increase needs
• Protein consumption – excess in USA
• 2.2 Pounds per Kilogram
#15 Calculating our protein needs
Convert weight to kilograms
2.2 Pounds per Kilogram
A healthy adult needs 0.8 grams protein per
kilogram
Example Calculation:
145 lbs = 65.9 kg
65.9 kg x 0.8 g/kg = 52 grams protein
needed per day
#16 Proteins in the Diet
• Protein quality
• Complete proteins
• Supply all essential amino acids
• Animal proteins, soy proteins
• Incomplete proteins
• Low in one or more essential amino acids
• Most plant proteins
• Complementary proteins
• Two incomplete proteins = complete protein
© Photodisc
Proteins in the Diet
• Meat, eggs, milk,
legumes, grains,
and vegetables are
all sources of
protein.
• Fruits contain
minimal amounts
and, along with fats,
are not considered
protein sources.
© Photodisc
#17 Vegetarian Diets
• Why people become vegetarians – religious,
environmental, prevent animal cruelty, health
benefits
• Types of vegetarians
• Lacto-ovo-vegetarian – eat dairy and eggs
• Semi-vegetarian
• Vegan – no animal products
• Health benefits vs. health risks
• Less fat, saturated fat, and cholesterol
• Restrictive diets may lack nutrients
• Careful planning needed for children, pregnant
women
#17 Dietary Recommendations for
Vegetarians
• Use complementary proteins to meet
protein needs
• Soy is a complete protein
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Choose a variety of foods
Choose whole, unrefined foods often
Choose a variety of fruits and vegetables
Choose lower fat dairy products, if used
Use a regular source of vitamin B12
The Health Effects of
Too Little Protein #18, 19
• Protein-energy malnutrition (PEM)
• Kwashiorkor
• Marasmus
• Nutritional Rehabilitation
#14,18 Protein Malnutrition
• Most Common during childhood in third
world
• In USA:
• In poverty
• Older adults
• Hospitalized patients with anorexia
nervosa, AIDA, cancer, malabsorption
• Can be corrected by a slow introduction of
calories and protein and vitamin
supplementation, fluids/electrolytes
#19 Marasmus
withering or waste away
• Chronic Protein Energy Malnutrition
• Protein, energy and nutrients are inadequate
• No fat stores or muscle mass
• Growth stops
• Short and Thin
• Metabolism slows, temperature drops
• Hair is sparse and falls out
• Usually 6-18 months old who are fed diluted or
improperly mixed formula
#19 Kwarshiorkor
evil spirit that infects first child when second child is
born 
• Breastfed until next child is born
• Baby is weaned and placed on a watered down
version of family diet that is low in protein or not
digested
• Lack of protein allows fluid to leak in tissues causing
edema
• Dry flaky skin
The Health Effects of
Too Much Protein #20
The Health Effects of Excess Protein
#20
• Excess Dietary Protein
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Kidney Function in those with renal issues
Mineral Losses, Magnesium and Calcium
Obesity
Heart Disease
Cancer
Gout
#21 Protein and Amino acid
supplements?
• Excess protein leads to excess body fat
• Intakes of calories and protein should match your
exercise and weight goals
• No benefit to extra protein and causes excess
nitrogen to be excreted which can lead to
dehydration
• Amino acid supplement can interfere with
absorption of other amino acids and cause
neurotransmitter alterations
#22 Good sources of non-meat
protein
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Soy protein – Tofu, soybeans
Beans and rice
Beans and corn
Rice and black eyed peas
Peanut butter on bread
Pasta and beans