PROTEIN
Vocabulary
Amino Group:
Denature:
Hormone:
Antibody:
Edema:
Intracellular Fluid:
Extracellular Fluid:
Deamination:
Ammonia:
Urea:
Kwashiorkor:
Marasmus:
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WHAT IS PROTEIN?
Proteins are a sequence of amino acids
Of the 20 amino acids that exist, 9 are essential amino acids, and 11 are non-essential
There are also 4 amino acids that can be considered conditionally essential: arginine, tyrosine,
glutamine, and cysteine
AMINO ACIDS: Structure
• Consist of a central carbon atom bonded to:
• The side group creates unique characteristics for each amino acid so they differ in: shape, size,
composition, electrical charge, and pH.
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AMINO ACID: Sequence
Amino acids link in specific sequences to form strands of protein
One amino acids is joined to the next by a PEPTIDE bond
Dipeptide –
Tripeptide –
Oligopeptides –
Polypeptide –
Proteins in the body and diet are long polypeptides (100s of amino acids)
DENATURING of PROTEINS
Acid, alkaline, heat, alcohol, and agitation can disrupt the chemical forces that stabilize
proteins can cause them to lose their shape (denature)
Denaturing of proteins happens during food preparation (cooking, whipping, adding acids) or
digestion (in the stomach with hydrochloric acid)
PROTEINS: Function
Structural Functions:
• Collagen – is the most abundant protein in mammals, and gives bone and skin their strength
• Keratin – provides structure to hair and nails
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Enzyme Functions:
• Enzymes are proteins that catalyze chemical reactions without being used up or destroyed in
the process
Examples?
Hormone Functions:
• Hormones are chemical messengers that are made on one part of the body, but act on cells in
other parts of the body
Examples?
Immune Function
• The Immune Response is a series of steps your body takes to mount an attack against invaders
• Antibodies are blood proteins that attack and inactivate bacteria and viruses
• Once an antibody has been made for a certain invader, your body can more quickly respond
(Immunization)
Fluid Balance
• Fluids in the body are intracellular or extracellular (interstitial and intravascular) and must
remain balanced
• Blood proteins like albumin and globulin help to regulate this balance by remaining in the
capillaries and attracting fluid
• Edema is the result of fluid imbalance
Acid-Base Balance
• Proteins help to maintain a stable pH level in our body fluid by picking up extra hydrogen ions
when conditions are acidic, and donating hydrogen ions when conditions are alkaline
• Otherwise, the resulting conditions of acidosis or alkalosis could lead to coma or death
Transport Functions
• Lipoproteins
• Albumin transports a variety of nutrients such as calcium, zinc, and Vitamin B6
• Transferrin transports iron (hemoglobin – a protein, contains iron, but it transports oxygen)
• Proteins may also acts as channels or pumps across the cell membrane
Energy Source
• If the diet does not provide enough energy, the body must begin to break down its own protein
(from enzymes, muscle, and other tissue)
• The proteins are broken down into individual amino acids, then deaminated, and the remaining
carbon, hydrogen, and oxygen compounds are used to make energy or glucose
• If the diet contains too much protein, the excess will be converted to glucose, or stored as fat
DIGESTION and ABSORPTION
MOUTH:
STOMACH:
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SMALL INTESTINE:
• Most protein absorption takes place in the duodenum and jejunum
• Most amino acids are absorbed into the bloodstream, but some remain in the enterocytes and
are used to synthesize enzymes and new cells
• >99% of protein enters the bloodstream as amino acids
• Absorption of whole protein can cause a severe allergic reaction
PROTEINS in the BODY
• Amino Acid Pool – amino acids that are available throughout the body (tissues and fluids) for
use when needed
• Protein Turnover – of the ~ 300 grams of protein synthesized by the body each day, 200 grams
are made from recycled amino acids
NITROGEN EXCRETION
• Amino acids breakdown yields an amino group (containing nitrogen)
• This molecule is unstable and is converted to ammonia
• Ammonia is toxic, so it is excreted from the cells and sent to the liver, where it is converted to
urea and water
• The urea is transported to the kidney, where it is filtered from the blood and finally sent to the
bladder for excretion in the urine
• Nitrogen is also lost through hair, skin, GI cells mucus, nails, and body fluids like sweat
How Much Protein Do We Need?
Adults:
Endurance Athletes:
Heavy weight lifters:
From The Gatorade Sport Science Institute:
High Protein Diets and Protein Supplements
Protein supplements or switching to a high protein diet is not effective for athletes who already get
enough calories and eat protein foods two to three times daily. Here’s why:
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Athletes get enough protein for muscle growth and repair in an average mixed diet.
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Protein from a food or a protein supplement acts the same in the body.
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Extra protein not needed by the body is burned for energy or stored as fat.
PROTEIN QUALITY
• Complete Proteins –
• Incomplete Proteins –
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PROTEIN: Health Effects
EXCESS DIETARY PROTEIN
• May strain the kidneys
• May cause mineral losses (especially calcium)*
• May increase risk of obesity*
• May increase risk of heart disease*
• May increase risk of cancer*
*only with animal protein
INSUFFICIENT DIETARY PROTEIN
• Protein-Energy Malnutrition (PEM) can occur anywhere in the world, but is most common in
developing countries
• Kwashiorkor
• Marasmus
• In industrialized nations, PEM may exist in the elderly population, in the poor, and those with
anorexia, cancer, AIDS, or malabsorption syndromes
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