PROTEIN
Structure of Protein
• Contains carbon, hydrogen, oxygen, and
nitrogen
• Remember carbohydrates and lipids contain carbon,
hydrogen, and oxygen – SO protein adds nitrogen
• Some proteins also contain sulfur, iron, copper,
phosphorus, or zinc
Structure of Protein
• Protein is made of chains of amino acids
• Which are considered “building blocks” of protein
• Created from 4 bonds around a carbon
atom
1. Carboxyl group (-COOH)
2. Amine group (-NH2)
3. Single hydrogen bond
4. Variable side group (letter “R”)
• Makes one amino acid different from another
Structure of Protein
• Watch the following:
https://www.youtube.com/watch?v=FKwSIu_XxnY
**will not need to know quaternary structure
Structure of Protein: Amino Acids
20 amino acids identified in the human body
• 11 made by the body
• NONESSENTIAL or DISPENSABLE
• Do not need to be a part of our diet
• 9 must be consumer from our foods
• ESSENTIAL or INDISPENSABLE
• Body cannot grow new tissue or maintain health without
these amino acids
Structure of Protein: Amino Acids
• Peptide bonds: bonds between two amino acids
• Connects amine group of one amino acid to
carboxyl group of another
• Water is the by product
• Peptide bonds create:
• Dipeptide: 2 amino acids
• Polypeptide: chain of multiple
amino acids bound together
Complete Protein vs. Incomplete Protein
• Contains all indispensable
• Lacking 1 or more
(essential) amino acids
• Most from animal sources
indispensable amino acid
• Found in grains and
vegetables
• Important for vegetarians
to combine 2 of the
following within 24 hours to
get the benefits of
complete protein
• Eggs, milk, fish, poultry,
meats
• Few plant products
include:
• Quinoa, amaranth, soybeans,
buckwheat, hempseed, chia
• Legumes
• Grains
• Nuts or seeds
• Dairy
Combine 2 incomplete proteins within 24 hours to get the benefits
of complete protein
Grains
Oats
Rice
Corn
Cereal
Whole wheat
Barley
Legumes
Milk
Dried peas
Kidney beans
Garbanzo beans
Peanuts
Cheese
Yogurt
Ice cream
Pudding
Seeds
& Nuts
Pumpkin
Sunflower
Poppy
Sesame
Walnuts
Pecan
Types of Vegetarians
• Pollo – does not eat red meat and fish (eats
chicken)
• Pesco pollo – does not eat red meat (eats
chicken & fish)
• Lacto – does not eat meat, fish, poultry, or
eggs/foods containing eggs (eats dairy products
like milk, cheese, & yogurt)
• Lacto ovo – does not eat meat, fish, and poultry
(eats dairy product & eggs)
• Vegan – avoids eating all animal products
Protein Structures
• Due to folding of chains of amino acids
• Primary structure of proteins is the order the
amino acids occur in the chain
• Secondary structure due to hydrogen bonding
between amino acid side chains
• Forms in 3 patterns:
1. Random coil (no specific
shape like a twisted Slinky)
1. Helix (coil like a Slinky)
2. Pleated sheet (paper fan)
Structure of Protein
• Tertiary Structure
• Globular proteins- do not tend to form links that will
create a protein network
• Ex: hemoglobin and lipoprotein
• Fibrous proteins- usually made from helix strands.
Strong and part of connective tissue
• Ex: collagen and elastin
Denaturation of a Protein
• Watch the following:
https://www.youtube.com/watch?v=3IL_Df5ouUc
Denaturation of a Protein
• Denaturation: any change of the shape of
the protein molecule without breaking its
peptide bonds
• Molecules unravel themselves and lose their
coiled structure
• Usually not reversible
Denaturation of a Protein
• Usually not reversible
• Return to its original shape when:
• Denaturation is slight
• Involve only hydrogen bond interactions
• Ex: lightly beating egg whites & gelatin
• Hold its shape when:
• Protein interact with other proteins while unfolded
• Breaking disulfide cross-links
• Often during coagulation
Methods of Denaturation
1. Temperature
• Heat is the most common agent
• Rate of increase is 600 times for every 10°C rise in
temperature
2. Mechanical actions
• Beating, rolling, and kneading
3. Chemical methods
• Lowering pH
4. Other physical methods
• Sound waves and irradiation
Coagulation of Proteins
• Results when a liquid protein forms clots
• Occurs when a protein is heated
• Examples: curdling milk to form cheese or cooking an
egg.
• When a protein is agitated
• When chemicals, such as acids, are added to a
protein
Coagulation of Proteins
• Milk proteins:
• Casein: will not coagulate unless high
concentrations of salt or acids are present
• Whey protein: coagulated by heat and
responsible for film on bottom and sides of
containers of heated milk
Coagulation of Proteins
• Over coagulation
• Changes taste and texture of foods
• Can ruin a recipe
• Overheated meat becomes tough/dry
• Over agitation of meringue causes clots to form
• Overcooked or overworked cheese results in rubbery texture
Functions of Protein in Foods
1. Form gels
2. Texturize
3. Emulsify
4. Form foams
5. Develop gluten
1. Form Gels
• Protein gelatin made from collagen extracted
from the bones and hides of animals
• Gelatin protein can be heated in water and then
cooled
• Milk and sugar can be heated to make
pudding/custard
2. Texturize
• Proteins can be texturized through
denaturation
• This process is used to make
• soybeans into meat substitutes
• processed cheeses
3. Emulsify
• Stable mixture of a fat and water based liquid
• Emulsifier: molecule that has a polar end and a non
polar end
• require heat or mechanical action to denature and form
the emulsion
• Egg yolks are an excellent emulsifier, as is milk and cheese
• Food products such as ice cream and mayonnaise require emulsifiers
to stay together
4. Form Foams
• Foam is a gas suspended in a liquid or semi solid
• Foams can be made by:
• using eggs or dairy
• incorporating air
• mechanical agitation
• by a sudden release in pressure (aerosol can)
• Examples of foams are: meringues, marshmallows,
whipped cream, and bread
5. Develop Gluten
• Gluten: elastic protein formed when wheat
flour is combined with moisture and
stirred/kneaded
• It coagulates when baked and forms an airy
texture, such as bread
Protein in the Body
1. Support growth and repair
2. Fight disease
3. Maintain fluid and mineral balance
4. Maintain pH balance
5. Control bodily functions
6. Provide energy
1. Growth and Repair
• Provides nitrogen and amino acids for growth and repair
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of the body
10,000 proteins have been identified in a single cell
Used to make muscle fibers, connective tissue, cell walls,
and red & white blood cells
Hair cells and nails also have a lot of protein
Whenever the body is injured, under stress, or ill; the
need for protein increases
Most body cells are replaced within a seven year period
Cells lining the intestinal tract are replaced every 3 days
Blood cells are replaced every 3-4 months
2. Fight Disease
• Antibodies are a type of protein made by the body when a
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disease or toxin is present
The body reproduces more antibodies for the next time
that the same germ comes into the body
A key function of protein is to protect the body from germs
and disease
Builds cells necessary to help get rid of parasites,
bacteria, and viruses
Only complete protein will give you these benefits
3. Maintain Body Fluid & Mineral Balance
• Help control movement of water and minerals
in/out of cells
• Too much water in cells – they burst
• Too little fluid – they will die
• Maintaining the right mineral balance is important
for nerves, brain, and muscles to function
normally
4. Maintaining pH Balance
• Proteins are very important to maintain your pH
balance
• Foods high in protein form acid and when eaten
they cause acid pH
• Therefore, balanced protein intake is necessary to
maintain a proper pH level
• Too much protein can cause blockages in blood
5. Control Bodily Functions
• Control hormones
• Regulates glucose levels in the blood
• Controls growth, regulated reproductive system, and
other critical body functions
• Control enzymes
• Necessary for most chemical reactions that occur within
the body
6. Provide Energy
• Body doesn’t store extra protein or turn it into
muscle
• When you consume extra protein, your body can
change the amino acids into an energy source
• NH2 is turned into ammonia, the C=O becomes
part of a compound known as ketones
• Both ammonia and ketones put a strain on the
kidneys