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Proteins
Proteins
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What Are Proteins?
Proteins are biomolecules that are made of C, O,
H, N and S.
The building blocks of proteins are amino acids.
What are amino acids?
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An amino acid is a molecule that has an carboxyl
group and an amino group. R represents the
radical or rest of the molecule.
Variable group
amino
group
carboxylic
acid group
hydrogen
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There are 20 different amino acids. Out of the
20, 8 are called essential.
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Essential amino acids are amino acids that the human
body cannot make (we do not have the enzymes to
produce them, thus we have to ingest them as part of
our food). Why? Because we need them to make our
own proteins.
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Cells link amino acids together by dehydration synthesis
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The bonds between amino acid monomers are called
peptide bonds
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The bond between an amino group of one
amino acid and the carboxyl group of another
amino acid makes a peptide bond.
What is missing in this equation? Fill in the
missing factors.
Amino Acid
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Amino Acid
Peptide Bond
Many amino acids are group together in a long
amino acid chain, this is called a polypeptide
chain.
ƒThe primary structure of a
protein is its unique
sequence of amino acids.
„ The
secondary structure of a protein is the
folding pattern of the polypeptide chain.
„ Two typical shapes of secondary structure are
coils (an alpha helix) or folds (beta pleated
sheets).
Amino acid
Primary
structure
chain
Secondary
structure
Alpha helix
Pleated sheet
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The tertiary structure of a protein is its
“packing pattern”. This is the active form of the
protein.
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The quaternary structure of a protein is a
complex association of several polypeptide
chains. Each of these polypeptide chains have a
primary, secondary and tertiary structure.
Collagen (gives your skin its strength) is formed
by several chain making like a rope.
Hemoglobin
(transports
oxygen) is another
example of
quaternary
structure
protein.
Primary
structure
Amino
acid
Secondary
structure
Hydrogen
bond
Alpha
helix
Pleated
sheet
Tertiary
structure
Polypeptide
(single subunit
of transthyretin)
Quaternary
structure
Transthyretin, with four
identical polypeptide subunits
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Denaturing is breaking the weak bonds that
keep the tertiary structure together. Heat, Ph
and high salt are factors that may denature
proteins.
Denaturing inactivates the protein.
Denaturing can be reversible.
Functions in humans
„ Proteins are involved in
„ cellular structure
„ Enzymes
„ movement
„ defense
„ transport
„ Communication
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Regulation.
The LEGUMES
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Legumes are members of the bean family Fabaceae
– they are dicots.
Legumes is synonymous with pod, the fruit
Examples of legumes: peas, beans, soybeans,
peanuts, lentils, clover, alfalfa
Importance of legumes
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Human nutrition: important sources of
Protein (bean, soybean, pea, peanut, etc.)
Oil (soybean, peanut, etc.)
Also, legumes are the major nitrogen fixers
Legumes have nitrogen-fixing bacteria in their
roots, in a symbiotic relationship
Bacteria take Nitrogen from air, and make it
usable for the plant – the Nitrogen Cycle
Legumes in the Nitrogen Cycle
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Nitrogen-fixing bacteria (Rhizobium) convert atmospheric
nitrogen (N2) into ammonia (NH3), which reacts with
water to produce ammonium (NH4+)
Nitrogen-fixing bacteria
live in symbiosis in roots
of legumes, forming
root nodules
Plants convert this nitrogen into
proteins or other nitrogen
compounds, which are then
consumed by animals
Legume roots
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Bacteria provides nitrogen to the plant
Plant provides carbohydrates to the bacteria
Features of Legumes
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Legumes are mostly herbaceous (not woody)
Usually have compound leaves
Mostly annuals, some perennials
Flowers are irregular,
with bilateral symmetry
Bees pollinate them,
triggers stamens
Legume seed and fruit
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Legume seeds are usually large, they have two
large cotyledons (seed leaves) – dicot
Cotyledons are filled
with stored food,
which helps the seed
to germinate
Legumes for food and forage
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Some examples of legumes used for food are:
Beans
Peas
Peanut
Soybean
Examples of legumes used for forage, animal feed:
Alfalfa
Clover
Vetches
Bean (Phaseolus vulgare)
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Bean come in different genera and species
Native to Mexico and the Andes in S. America
Beans are very rich in protein (25%) and some
carbohydrates
Hundreds of species
and varieties: pinto,
navy, black, kidney,
lima, pink, red, broad,
fava, white, and
mung bean
Why do beans give you gas?
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Beans have complex carbohydrates that are indigestible by
humans…
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These go down to the intestines, where bacteria go crazy
eating these carbohydrates…
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As a result, the bacteria start producing methane gas,
which accumulates and… you know the rest!
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To avoid this: rinse beans well, cook them long;
treat with enzymes like “Beano” –helps to eliminate and
break down these complex carbs.
Peas (Pisum sativum)
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Pisum sativum is the common garden pea
Originated in the Near East
Rich in protein and carbohydrates
Many varieties, including
snow peas (where immature
pod is eaten whole);
Green peas, split peas,
Chick peas (garbanzos)
Lentils
Peanut (Arachis hypogaea)
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The peanut is native to South America, cultivated
by the Aztecs… later introduced to Africa, U.S.,
Asia, etc.
Rich in oil and protein
Very unusual growth pattern:
peanuts sow their own seeds!
Upon fertilization, ovary grows
down, buries ovules into the
ground, where pods mature into
the peanut fruit
Peanuts are called “ground nuts”
Peanut uses
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Half of US peanut crop production is for peanut
butter
Also for snack foods, candy, peanut oil, animal
feed
Dr. George Washington Carver
(1865-1943); brilliant scientist,
agriculturist at Tuskegee Institute
in Alabama; discovered
325 uses for peanuts!
Soybean (Glycine max)
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Native to China, but now
grown worldwide
Rich in oil and protein. Uses:
Cooking oil, salad dressings, mayonnaise, marg.
Protein to make textured vegetable protein (TVP) as meat
substitute, as animal feed
Soy sauce: fermented soybeans and grain
Tofu: soy milk curds
Miso: fermented soybean and rice paste (Japan)
Soybeans eaten as sprouts, snacks, health food
Oil used to make diesel fuel, plastics, paint, ink
Forage legumes
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Worldwide, some legumes are grown as pasture or forage
crops: their high protein content makes them ideal as
animal food.
Alfalfa (Medicago sativa)
is grown extensively
as animal feed
Trifolium species; true clovers, are also grown as pasture –
some are now grown with other crops to provide nitrogen
and protect the soil
Vicia – vetches are planted to prevent soil erosion