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: a hydrogen, a carboxylic acid, an amino group, and an additional side group that is unique to each amino acid

AMINO ACIDS: Structure

• The side group creates unique characteristics for each amino acid so they differ in: shape, size, composition, electrical charge, and pH.

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

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)

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)

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

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

PROTEIN: Functions

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)

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)

PROTEIN: Functions

FLUID BALANCE

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

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

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

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

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

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

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)

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

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

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

• >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 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

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

Protein SourcesAlmonds (1 cup) 24 grams

Pinto Beans (1 cup) 15 grams

Cheese (1 oz.) 7 grams

Ham (3 oz.) 18 grams

1 Egg 6 grams

2% Milk (1 cup) 8 grams

Clams (3 oz.) 60 grams

Whole Wheat Bread 3 grams

Lean Hamburger 30 grams

Peanut Butter (1 T) 4 grams

Salmon (3 oz.) 20 grams

Tofu (4 oz.) 9 grams

Yogurt (8 oz.) 10 grams

White rice (1 cup) 4 grams

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

PROTEIN: Health EffectsINSUFFICIENT 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

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

VEGETARIANISM

• What are the PROS and CONS of vegetarianism?

ATKIN’S DIET

• How does it work?

• What are some of the possible negative consequences?