Download Biochem15_Proteins

Chapter
6
Proteins
and Amino
Acids
Photo courtesy of the USDA
Protein
• The word protein was coined by the Dutch
chemist Gerardus Mulder in 1838, and comes
from the Greek word protos, meaning “of
prime importance.”
Protein
• Proteins are a major component of all plant
and animal tissues, second only to water.
• When we eat more protein than we need, the
excess is either used to make energy or is
stored as fat.
Protein Deficiency
• When the diet lacks protein, the body breaks
down tissues such as muscle and uses it as a
protein source.
• This causes loss, or wasting, of muscle, organs,
and other tissues.
• Protein deficiency also increases susceptibility
to infections and impairs digestion and
absorption of nutrients.
Amino Acids Are the
Building Blocks of
Protein
• Proteins are sequences of
amino acids
• Types of amino acids
• Essential: must come from
diet
• Nonessential: can be made in
the body
Amino Acids Are the
Building Blocks of
Protein
• Protein structure
• Chain of amino acids
• Sequence of amino acids determines shape
• Shape of protein determines function
• Denaturing protein structure
• Disrupts function
• Caused by heat, acid, oxidation, agitation
Functions of Body Protein
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 absorbed into the bloodstream
Proteins in the Body
• Protein synthesis
• Directed by cellular
DNA
• Amino acid pool
• Protein turnover
• Synthesis of nonprotein substances
Proteins in the Body
• Protein excretion
• Deamination of amino acids
• Amino groups converted to urea for excretion
• Nitrogen balance
• Nitrogen intake vs. nitrogen output
Proteins in the Diet
• Recommended protein intake
• Adult RDA = 0.8 grams/kilogram body weight
• Infant RDA = ~ 1.5 grams/kilogram body weight
• Protein consumption
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
• 2 incomplete proteins = complete protein
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Proteins in the Diet
• Evaluating protein quality
• Amino acid composition
• Digestibility
• Protein Digestibility–Corrected Amino
Acid Score (PDCAAS)
• Used to determine %DV
• Protein and amino acid supplements
• Generally not needed with risks unknown
Pros and Cons of
Vegetarian Eating
• Types of vegetarian diets
• Semi-vegetarian
• Lacto-ovo vegetarian
• Vegan
• Health benefits vs. health risks
• Less fat, saturated fat, and cholesterol
• Restrictive diets may lack nutrients
• Careful planning needed for children, pregnant
women
The Health Effects of
Too Little Protein
• Protein-energy malnutrition (PEM)
• Kwashiorkor
• Marasmus
The Health Effects of
Too Much Protein
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.
Proteins Act as Carriers
• Lipoproteins have
embedded proteins
that help them
transport fat and
cholesterol in the
blood.
Protein and Gout
• A recent study sought to
explore whether or not the
risk of gout is
independently increased by
consumption of (1) a
protein-rich diet, (2) a diet
high in meat, and (3) a diet
high in seafood.
• The results showed that a
protein-rich diet was not
associated with an
increased risk of gout.
However, the risk of gout
increased 21 percent per
additional portion of meat
per day and 7 percent per
addition portion of seafood
per week. The study also
found that consumption of
dairy protein (especially in
low-fat dairy products)
reduced risk of gout.
ADA Position on
Vegetarian Eating
• It is the position of the American Dietetic
Association and Dietitians of Canada that
appropriately planned vegetarian diets are
healthful, nutritionally adequate, and provide
health benefits in the prevention and
treatment of certain diseases.
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.
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.
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