Protein
Structure
- large, complex molecules made up of amino acids
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-
Found as essential components of all living cells
-
Made of carbon, oxygen, hydrogen and nitrogen
-
Structure is determined by DNA
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Amino acids
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
Proteins are made of amino acids (AA) bonded
together in specific sequences (each can be
hundreds of AAs long)

But there is only 20 different amino acids that are
used in different combinations to make the
hundreds of thousands of different proteins we
use

9 of the 20 are ESSENTIAL amino acids (our
body can not produce them, therefore we MUST
get them from your diet)
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THE 20 AMINO ACIDS
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9 essential amino acids: histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, threonine, tryptophan and valine.
Amino Acid Structure
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2 Aas = dipeptide
Peptide bond
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 After
peptides are made they fold up
because the AAs are attracted to each
other and form weak intermolecular
bonds
 Sequence
of AAs determines the 3D
shape it will form
 The
3D shape of a protein is what
determines its function in the body
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HEMOGLOBIN - Protein found
in red blood cells that carries
oxygen molecules to the cells
and carbon dioxide away from
the cells
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Denaturation of Protein
 Loss
of shape of protein
 This
is caused by excess heat, pH
changes, heavy metals, alcohol etc
 Denatured
proteins can’t work properly
due to loss of 3D structure
 Deficient
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AAs can limit protein synthesis
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Dietary Protein sources

Food Sources:


Mutual supplementation – foods can be combined to
provide a complete source of protein (e.g. beans and
rice), but should be during the same day, so protein
synthesis is not limited
 The incomplete proteins that are combined are called
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“complementary proteins”

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Meat, fish,eggs, poultry, dairy products,
legumes, nuts and seeds. (Breads, cereals and
vegetables also contain small amounts of protein.)
“high quality” proteins – contain all the essential amino
acids
A complete protein

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source is one that provides all of the essential
amino acids. You may also hear these sources
called high quality proteins. Animal-based foods; for
example, meat, poultry, fish, milk, eggs, and cheese
are considered complete protein sources.
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An incomplete protein

source is one that is low in one or more of the
essential amino acids.Complementary proteins are
two or more incomplete protein sources that
together provide adequate amounts of all the
essential amino acids.
1. Stomach
- pH is low (1-3)
- denature proteins
Pepsin
polypeptides
amino acids +
smaller polypeptides
2. Duodenum
- neutral pH
(because of sodium
bicarbonate from the
pancreas)
stops the action of pepsin
proteases
Peptide
amino acid
peptidases
Proteases – from the pancreas
Peptidases – from the
intestinal cells
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3. Jejunum
– AAs are
absorbed into the
blood stream and
travel to the liver
Function of Proteins

Function in the Body:






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Provides energy, but not the preferred energy source,
but will be used if there is not enough carbs or fats
Cell growth, repair and maintenance.
Help to build, maintain, and repair body tissues.
Enzymes, antibodies, neutrotransmitters, haemoglobin,
and some hormones (e.g. insulin) are made of protein
Maintain fluid and electrolyte levels
Proteins help to maintain acid-base balance in the
blood
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Problems with excess dietary
proteins
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1.
High cholesterol (high protein diets)
2.
Bone loss (high protein diets –
sulphur amino acids – pull Calcium
from bones)
3.
Kidney disease (diabetics) – too
much urea production in the kidney
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