1 dnt 200 nutrition for health sciences protein. 2 when mighty roast beef was the englishman’s...

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DNT 200NUTRITION FOR HEALTH

SCIENCES

PROTEIN

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PROTEIN

When mighty roast beef was the Englishman’s food,

It ennobled our hearts and enriched our blood,

Our soldiers were brave and our courtiers were good.

Oh! the roast beef of old England!

Richard Leveridge

(1670-1758)

English singer and composer

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PROTEIN

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PROTEIN

DEFINITION

Proteins are compounds composed of carbon,

hydrogen, oxygen, and nitrogen atoms

arranged into amino acids linked in a chain. Some amino acids also

contain sulfur atoms

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PROTEIN

AMINO ACIDS

Amino Acids are compounds that serve as the building blocks of proteins; each contains an amino group, an acid group, a hydrogen atom, and a distinctive side group attached to a central carbon atom– Nine essential amino acids– Thirteen non-essential amino acids– Some are able to be manufactured by chemists

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PROTEIN

AMINO ACIDS

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PROTEIN

AMINO ACIDS

Essential Amino Acids -- Amino Acids that the body cannot synthesize in amounts sufficient to meet physiological need

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PROTEIN

AMINO ACIDS

Essential Amino Acids

Valine

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PROTEIN

AMINO ACIDS


Leucine

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PROTEIN

AMINO ACIDS


Isoleucine

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PROTEIN

AMINO ACIDS


Threonine

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PROTEIN

AMINO ACIDS


Lysine

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PROTEIN

AMINO ACIDS


Sulfur Containing Amino Acids(Grouped together because if the body has enough

Methionine, it can change it into Cysteine)

Methionine Cysteine (non-essential)

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PROTEIN

AMINO ACIDS


Aromatic Amino Acids (contain benzene ring)(Grouped together because if the body has enough

Phenylalanine, it can change it into Tyrosine)

Phenylalanine Tyrosine (non-essential)

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PROTEIN

AMINO ACIDS


Tryptophan

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PROTEIN

AMINO ACIDS


Histidine

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PROTEIN

AMINO ACIDS

Essential Amino Acids• Need to be obtained from foods• Sometimes a non essential amino acid

can be come essential -- Examples– Illness can demand requirements beyond the

body’s ability to produce the amino acid– In Phenylketonuria (PKU) the body is unable to

convert phenylalanine to tyrosine, therefore tyrosine becomes essential

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PROTEIN

AMINO ACIDS

Non-essential Amino Acids -- Amino Acids that the body is able to manufacture

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PROTEINAMINO ACIDS

Non-essential Amino Acids• Alanine• Arginine

• Asparagine• Aspartic Acid

• Cystine• Glutamic Acid

• Glutamine• Glycine• Proline• Serine

• Tyrosine

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PROTEIN

SURFACE STRUCTURE• Have a great variety of surface structures

(shapes) to perform distinct, individual, and specialized functions

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PROTEIN

SURFACE STRUCTURE

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PROTEINSURFACE STRUCTURE

Human insulin is identical to pig insulin, except that the last amino acid of the B-chain for the pig is alanine (Ala) instead of threonine (Thr)

Ala

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PROTEIN

• The average amino acid weighs 6.25 times as much as the nitrogen it contains, therefore

• Nitrogen represents 16% of the weight of the protein

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PROTEIN

DIGESTION AND ABSORPTION

• Role of protein is not to provide the body with proteins, but to supply amino acids from which the body can make protein

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PROTEIN


• Hydrolysis of proteins begins in the stomach– HCl uncoils (denatures)

the protein’s tangled strand so that digestive enzymes can attack the peptide bonds

HCl

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PROTEIN


– Pepsin (a gastric protease) cleaves proteins -- large polypeptides are broken down into smaller polypeptides

– When these polypeptides enter the small intestine pancreatic and intestinal proteases hydrolyze them further into short peptide chains (oligopeptides) tripeptides, dipeptides, and amino acids

Pepsin

Proteases

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PROTEINDIGESTION AND

ABSORPTION

– Peptidase enzymes on the surface of the intestinal cells break more of the peptide bonds

– A mixture of free amino acids, dipeptides, and tripeptides is left

– Distinct carriers then transport these pieces across the intestinal cells for passage into the blood

Absorption

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PROTEINPROTEINS IN THE BODY

FunctionsEnzymes• Enzymes are proteins that facilitate

chemical reactions without being changed in the process

• Are essential to all life processes• Are protein catalysts

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FunctionsEnzymes (continued)• Act upon other proteins

– You eat protein– Digestive enzymes (proteins) break down protein into

amino acids– Amino acids enter the cells where proteins (enzymes) put

them together into long chains whose sequence is specified by genes

– Chains fold and twist themselves to form proteins; some of these proteins become enzymes themselves

– These enzymes may then be used to break apart or put together other compounds

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FunctionsFluid Balance• Fluids are present in

several body compartments– Spaces inside blood vessels– Spaces within the cells

(outside the blood vessels)

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PROTEIN

PROTEINS IN THE BODY

Functions

Fluid Balance (continued)

• Fluids go back and forth in these spaces and proteins (together with minerals) help to maintain the needed distribution of these fluids

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FunctionsFluid Balance (continued)

– Proteins are large

– Proteins are attracted to water (hydrophilic)

– Being large, proteins cannot pass freely across cell membranes that separate body compartments

– Attracting water makes proteins even larger

– A cell wants to keep a certain amount of water in its interior space but can’t manufacture the water directly

– The cell can manufacture protein and these proteins will hold water

– Therefore, the cell uses proteins to regulate the distribution indirectly

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PROTEIN

PROTEINS IN THE BODYFunctions

Acid-Base Balance• Acids are compounds that release hydrogen

ions in solution• Bases are compounds that accept hydrogen

ions in a solution• Acid-Base Balance is the equilibrium in the

body between acid and base concentrations

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FunctionsAcid-Base Balance (continued)• Normal body processes continually produce

acids and bases, which must be carried by the blood to the organs of excretion

• Blood must do this without allowing its own acid-base balance to be affected

• Proteins act as buffers, picking up hydrogens (acid) when there are too many and releasing them when there are too few

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FunctionsAcid-Base Balance (continued)• Acidosis

– Results when the blood pH limit falls below 7.35 and causes proteins to undergo denaturation -- they loose their shape and ability to function

– Disturbing a protein’s shape renders it useless e.g. hemoglobin looses its capacity to carry oxygen (if unchecked, can be fatal)

• Alkalosis– Results when the blood pH limit rises above 7.45– Can cause coma or death

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FunctionsAcid-Base Balance (continued)

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FunctionsAcid-Base Balance (continued)

• By accepting and releasing hydrogen ions, proteins act as buffers maintaining acid-base balance of the blood and body fluids

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PROTEIN


Antibodies• Antibodies are large proteins

of the blood and body fluids, produced by the immune system in response to the invasion of the body by foreign molecules (usually proteins called antigens)

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PROTEIN


Antibodies (continued)• Combine with and inactivate the foreign

invaders, thus protecting the body• Act against viruses, bacteria, and other

disease agents• Without adequate protein, the body cannot

maintain its resistance to disease (immunity)

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FunctionsHormones• Hormones are messenger

molecules• Are secreted by a variety of

endocrine glands in response to altered conditions in the body

• Each travels to one or more specific target tissues or organs where is elicits a specific response

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FunctionsHormones (continued)• Some are made up of amino acids (others

are sterols such as testosterone)• Examples

– Insulin and glucagon help regulate the blood glucose

– The thyroid hormone helps regulate the body’s basal metabolic rate

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FunctionsTransport Proteins• Some act as pumps picking up compounds

on one side of cell membranes and depositing them on the other side

• Others move about in body fluids carrying nutrients and other molecules from one organ to another

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PROTEIN

PROTEINS IN THE BODY

FunctionsTransport Proteins

(continued)• Examples

– Hemoglobin -- carries oxygen from the lungs to the body’s cells

– Lipoproteins transport lipids around the body

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FunctionsBlood Clotting• Fibrin, a stringy insoluble mass of protein

fibers, facilitates blood clotting

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FunctionsVisual Pigments• Opsin, the protein portion of

the visual pigment molecule in the cells of the retina, responds to light by changing its shape thus initiating the nerve impulses that convey the sense of light to higher brain centers

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PROTEIN


Structural Proteins• Collagen

– Is the main fibrous protein (others are elastin and keratin)

– Helps make scar tissue, forms the matrix of bones and teeth

– Forms the material of ligaments and tendons

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PROTEIN

PROTEINS IN THE BODYPressure Sores

• Also known as decubitus ulcers, bed sores• Caused by

– Unrelieved pressure on the skin and underlying tissues– Friction (being pulled across bed sheets)– Shear (sliding down in a bed or chair causing the skin to fold

over itself and cutting off blood supply)– Poor nutrition, especially protein, may lead to skin

breakdown

• Four stages

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PROTEIN


• Stage 1– Redness and heat over a pressure point

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PROTEIN


• Stage 2– Destruction of the epidermis and partial

destruction of the dermis

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PROTEIN


• Stage 3– All the layers of the skin are destroyed and a deep

crater forms

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Pressure Sores• Stage 4

– Ulcer extends through the skin and subcutaneous tissues and may involve bone, muscle, and other structures.

– Patient experiences fluid loss, pain, and is at great risk for infection.

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PROTEIN

PROTEINS IN FOODS• Role is not to supply the body protein

directly but to supply amino acids from which the body can make its own protein

• Protein Quality– Complete Protein is a protein that contains all

the amino acids essential in human nutrition in amounts adequate for human use

• Must contain the nine essential amino acids and enough nitrogen and energy for the synthesis of the other thirteen

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PROTEINPROTEINS IN FOODS

• Protein Quality (continued)• Body makes only complete proteins

– Body uses amino acids in a specific ratio to one another

– If one amino acid is supplied in an amount smaller than needed, synthesis will be limited

» Concept of the limiting amino acid

» A chain is only as strong as its’ weakest link

» The limiting amino acids are the sulfur containing ones (methionine and cysteine), tryptophan, and lysine-- these are a little harder to get than the others

• Dietary protein will not be used efficiently when energy from carbohydrate and fat is lacking (protein sparing effect of carbohydrate and fat)

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PROTEIN

PROTEINS IN FOODS

• Protein Quality (continued)• Generally, proteins from animals is

complete protein (exception is gelatin)

• Plant protein is variable– Corn protein is incomplete

– Soy protein is complete

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PROTEIN

PROTEINS IN FOODS

• Protein Quality (continued)• Complementary Protein -- two or more

proteins whose amino acid assortments complement each other in such a way such that the essential amino acids missing from one are supplied by the other

– The educated vegetarian can choose a diet that is adequate in protein by choosing a variety of legumes, grains, and vegetables

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• Protein Quality (continued)– Digestibility

• Digestibility is a measure of the amount of amino acids absorbed from a given protein intake

• High quality protein is an easily digestible complete protein

– Reference Protein• Egg protein

• Used by the Food and Agriculture Organization (FAO) and World Health Organization (WHO) as a standard against which to measure the quality of other proteins

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SOURCES• Milk -- 8 grams per cup• Meat -- 7 grams per ounce• Vegetables -- 2 grams per 1/2 cup• Starch/bread -- 3 grams per serving• Fruits -- negligible• Fats -- negligible

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SOURCES

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PROTEINHEALTH EFFECTS OF PROTEIN

• Protein Energy Malnutrition (PEM)– Protein Energy Malnutrition is a deficiency of both

protein and energy

– Kwashiorkor -- a form of PEM that results either from inadequate protein intake or, more commonly, from infections

• Is the Ghanaian name for “the evil sprit that infects the first child when the second child is born”

• Theory -- May be a form of food poisoning superimposed on malnutrition

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• Protein Energy Malnutrition (PEM)– Kwashiorkor (continued)

• Symptoms– Growth slows

– Hair looses color

– Skin becomes patchy and scaly (sometimes with ulcers and sores that fail to heal)

– Limbs and face become swollen with edema (protein in the blood becomes depleted and water cannot be held there, instead it seeps into interstitial space and accumulates)

– Belly bulges with fatty liver

– Sickens easily, becomes weak, fretful, and apathetic

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PROTEIN

HEALTH EFFECTS OF PROTEIN


• Occurs on every continent

• Typically sets in at the age of two

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• Protein Energy Malnutrition (PEM)– Marasmus -- the disease of starvation

• Occurs in persons who receive little of no food• Marasmic child looks like “skin and “bones”• Often sick because resistance to disease is low• Muscles are wasted, including the heart• Little or no fat to insulate against the cold• Occurs most commonly in children 6-18 months old• Impairs brain development

– Brain normally grows to adult size by 2 years of life– May have permanent effect on learning ability

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PROTEIN

HEALTH EFFECTS OF PROTEIN• Protein Energy Malnutrition (PEM)

– Marasmus

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PROTEIN

HEALTH EFFECTS OF PROTEIN• Protein Energy Malnutrition (PEM)

– Marasmus

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Body’s Priority System (Protein Priority System)1. Abandons less vital systems first (hair and

pigments which are made of amino acids) are the first to go

2. Antibodies are degraded so their amino acids can be used as building blocks for the heart, lungs, and brain tissues

3. Resistance to infection is therefore lowered4. Malnutrition and infection are a deadly

combination

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• Protein Excess– No Benefits

• Excess NH2 must be excreted causing kidneys to work harder

• Excess amino acids are stored as fat– Risks

• Obesity -- protein-rich foods are often high fat foods• The more protein consumed, the more likely fruits

and vegetables will be crowded out of the diet, making in inadequate in other nutrients

• Studies suggest diets high in protein promote calcium excretion

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PROTEIN

RECOMMENDED PROTEIN INTAKES

• Body Losses– Skin cells flake off or are rubbed off every day

– Hair and nails grow longer and are shed or cut away

– People need to replace losses

• If the body is growing, the needs are greater than just for maintenance

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PROTEINRECOMMENDED PROTEIN INTAKES• Nitrogen Balance -- the amount of

nitrogen consumed (N in) as compared with the amount of nitrogen excreted (N out)– If the body maintains in its tissues the same

amount of protein from day to day it is in nitrogen balance

– If the body looses protein it is in negative nitrogen balance

• Fasting• Starvation• Illness• Burn victims (forced to use protein for energy)

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PROTEIN


• If the body gains protein it is in positive nitrogen balance

• Growing children

• Pregnant women

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PROTEIN


DIETARY REFERENCE INTAKE VALUE

• AI– Males over 18 -- 56 grams– Females over 18 -- 46 grams

• RDA– Healthy adults over 18 need 0.8 grams of high

quality protein per kilogram of appropriate or average body weight for height

2002 Data

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PROTEIN


• Assumptions• Protein eaten will be of high quality

• It will be consumed with adequate energy from carbohydrate and fat

• Other nutrients in the diet will be adequate

• Individual is healthy and there is no unusual metabolic need for protein

1 dnt 200 nutrition for health sciences protein. 2 when mighty roast beef was the englishman’s...

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amino group

amino acidsgrouped

acid group

building blocks of proteins

roast beef of old england

hydrogen atom

nitrogen atoms

richard leveridge