WHAT IS PROTEIN

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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

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AMINO ACIDS Structure

• Consist of a central carbon atom bonded to a
  hydrogen, a carboxylic acid, an amino group, and
  an additional side group that is unique to each
  amino acid

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AMINO ACIDS Structure

• 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

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AMINO ACID Sequence

• Dipeptide 2 amino acids
• Tripeptide 3 amino acids
• Oligopeptides 4-10 amino acids
• Polypeptide more than 10 amino acids
• Proteins in the body and diet are long
  polypeptides (100s of amino acids)

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DENATURING of PROTEINS

• Acid, alkaline, heat, alcohol, and agitation can
  disrupt the chemical forces that stabilize
  proteins and 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)

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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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PROTEIN Functions

• ENZYMES
• Enzymes are proteins that catalyze chemical
  reactions without being used up or destroyed in
  the process
• Used in digestion, releasing of energy from
  nutrients for fuel, triggering reactions that
  build muscle and tissue

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PROTEIN Functions

• HORMONES
• Hormones are chemical messengers that are made on
  one part of the body, but act on cells in other
  parts of the body
• Insulin, Glucagon
• Antidiuretic Hormone (ADH)

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PROTEIN Functions

• 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)

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PROTEIN Functions

• FLUID BALANCE
• Fluids in the body are intracellular or
  extracellular (interstitial and intravascular)
  and must remain balanced

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PROTEIN Functions

• FLUID BALANCE
• 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

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PROTEIN Functions

• 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

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PROTEIN Functions

• TRANSPORT
• Lipoproteins (chylomicrons, LDL, HDL)
• 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

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PROTEIN Functions

• ENERGY SOURCE
• If the diet does not provide enough energy, the
  body must begin to break down its own protein
• 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

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DIGESTION

• No digestion of protein takes place in the mouth,
  it begins in the stomach
• Hydrochloric acid denatures protein and also
  converts pepsinogen to pepsin
• Pepsin breaks the protein down into peptides of
  various lengths and some amino acids
• Pepsin completes 10-20 of digestion

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DIGESTION

• Pancreas makes trypsinogen and chymotrypsinogen
  (proenzymes) in response to protein in the small
  intestine
• They will be activated to trypsin and
  chymotrypsin (now called proteases)
• Proteases break down polypeptides into smaller
  peptides (very few peptides have been broken down
  to amino acids at this stage)

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DIGESTION and ABSORPTION

• The intestinal wall produces peptidases which
  continue to split the remaining polypeptides into
  tripeptides, dipeptides, and some amino acids
• These smaller units are transported into the
  enterocytes

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ABSORPTION

• In the enterocyte, other peptidases immediately
  digest everything into single amino acids which
  are absorbed into the bloodstream
• Some amino acids share the same transport system,
  so if you take in a large amount of one
  particular amino acid, you may be inhibiting the
  absorption of others

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ABSORPTION

• 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
• gt99 of protein enters the bloodstream as amino
  acids
• Absorption of whole protein can cause a severe
  allergic reaction

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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

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NITROGEN EXCRETION

• Amino acid 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 (page
  227)
• Nitrogen is also lost through hair, skin, GI
  cells mucus, nails, and body fluids like sweat

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How Much Protein Do We Need?

• Adults
• 0.8 grams of protein per kilogram of body weight
  per day
• Endurance Athletes
• 1.2 to 1.4 g/kg/day
• Heavy Weight Trainers
• 1.7 to 1.8 g/kg/day

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Protein Sources
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PROTEIN QUALITY

• Complete Proteins proteins that provide all the
  essential amino acids (most animal proteins)
• Incomplete Proteins proteins that are missing
  one or more essential amino acids (most plant
  proteins except soy protein)
• Incomplete proteins can be served with a
  complementary protein to make it complete

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PROTEIN Health Effects

• 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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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

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VEGETARIANISM

• What are the PROS and CONS of vegetarianism?

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ATKINS DIET

• How does it work?
• What are some of the possible negative
  consequences?

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