Ch06 Proteins

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Chapter 6: Proteins & Amino Acids

Copyright 2012 John Wiley & Sons, Inc. All rights reserved.


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Proteins & Amino Acids

The word protein comes from the Greek

proteios meaning of primary importance

Protein are essential to every cellular funtion

Catalyze chemical reactions

Fundamental components of skeletal and

muscular tissue

Vital to inmune response

2012 John Wiley & Sons, Inc. All rights reserved.


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Student learning outcomes: At the end

of this chapter, you should be able to:

Describe the role of proteins and amino acids

in health and disease

Plan a diet to meet protein recommendations


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THINK about thisthen share within

a PAIRthen SHARE with the class

What do you know about proteins and amino

acids?

What are benefits of eating plant foods over

animal foods?


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Sources of protein

Animal: meat, eggs, dairy products High in saturated fat and cholesterol; provide B

vitamins and some absorbable minerals (iron, zinc,calcium) low in fiber

Plant: grains, nuts, legumes Low in saturated fat and cholesterol; high in fiber,

phytochemicals, and unsaturated fat Legumes: starchy plant seeds producing bean pods,

including peas, peanuts, beans, soybeans, lentils,chickpeas


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Sources of protein

Animal products are high on protein, iron, zinc, and calcium but also

add saturated fat and cholesterol to the diet


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Sources of protein

Plant source of

protein are rich in

fiber, phytochemical,

and monosaturated

and polysaturated

fats


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Amino acids: building blocks of proteins Carbon, hydrogen, amino group (contains nitrogen),

acid group, and side chain

20 different side chains make 20 different amino

acids

Amino acids

The generalstructure

of an amino acid


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Building blocks

Match the building blocks with the nutrient:

____ complex carbohydrates a) amino acids

____ triglycerides b) fatty acids and glycerol

____ proteins c) polysaccharides


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Amino acids link to form proteins

Aminoacids linked by

peptide bonds are

called peptides. When

two amino acids are

linked, they form a

dipeptide; three form atripeptide. Many amino

acids bonded together

constitute a

polypeptide.

Polypeptide chains may

contain hundreds of

amino acids.

The order and chemical

properties of the amino

acids in a polypeptidechain determine how

the polypeptide folds

and, hence, the three-

dimensional shape of

the protein.


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Amino acids link to form proteins

We obtain amino acids from eating plant andanimal foods.

Our bodies reassemble the amino acidbuilding blocks into our body proteins.


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Essential vs. non-essential amino acids

Essential/indespensible: Cannot be made in

the body so essential to eat them

If one is missing, body proteins are broken down to

make new proteins

Non-essential/despensible: Body can make

them from other proteins so not essential to

eat them


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Twenty amino acids are

commonly found in

proteins. The table show

here lists them based on

whether they are essential

or nonessential and

indicates those that are

conditionally essencial


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Amino acids structure


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Grupo I. Aminocidos apolares. Aminocidos cuyo resto R

no es polar. Esto es, no posee cargas elctricas en R al tener

en l largas cadenas hidrocarbonadas. Estos aminocidos, si

estn en gran abundancia en una protena, la hacen insoluble

en agua.

Grupo II Aminocidos polares no ionizables. Poseen

restos con cortas cadenas hidrocarbonadas en las que

hay funciones polares (alcohol, tiol o amida).

Contrariamente al grupo anterior si una protena los tiene

en abundancia ser soluble en agua.

Grupo III Aminocidos polarescidos. Pertenecen a este grupo

aquellos aminocidos que tienen

ms de un grupo carboxilo. En las

protenas, si el pH es bsico o

neutro, estos grupos se encuentran

cargados negativamente.

Grupo IV Aminocidos polares

bsicos. Son aquellos aminocidosque tienen otro u otros grupos

aminos. En las protenas, estos

grupos amino, si el pH es cido o

neutro, estn cargados

positivamente.

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Relacin de los aminocidos y sus

abreviaciones correspondientes


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FoodA Food B


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Can you use only the amino acids

from FoodA to make this protein?


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The yellow triangle is anon-essential amino acid


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The blue square is alimiting amino acid


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from Food B to make this protein?


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from FoodsA and B to make this protein?


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Did you use all of the amino acids

from FoodsA and B to make this protein?

It not, what did the body do with the extras?


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FoodsA and B are complementary: each

supplies some amino acids for the full set

of needed amino acids


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Essential amino acids

Cannot be made

Need to be eaten

Non-essential amino acids

Can be made from others


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What a scientist sees


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Protein folding

Amino acids interact to form the 3-dimensional

structures of proteins

Structures of proteins determines their functions

If protein structure is changed, then protein function

may change

+ -+ -


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Protein folding

The final structure of

a protein molecule

consists of one ormore folded

polypeptide chain


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Protein denaturation

Denaturation:change in a proteins three-dimensional shape

Occurs with: Heat from cooking or a fever

Low pH in the stomach or when the body becomes

acidic (for example, in diabetic ketoacidosis)

Neurodegenerative diseases such as Alzheimersdisease, mad cow disease, Parkinsons disease


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Protein denaturation

Denaturation. Alteration of a proteins three-dimensional structure


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Concept check

Which chemical element is found in protein butnot in carbohydrate or lipid?

What determines whether an amino acid mustbe consumed in the diet?

What determines the shape of a protein?

How does denaturation affect protein function?


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Protein

digestion


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Application

Insulin is a protein. Why do diabetics need to

inject insulin rather than take it orally?


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The purple amino acids are absorbed by the same

transport system as the green amino acids. If youconsume a sports drink that is supplemented withthe green amino acids what will happen to theabsorption of the purple ones.

Protein digestion

a) nothingb) the larger amount of green ones

will limit the absorption of thepurple ones

c) the small amount of the purpleones will be absorbed first

d) both will be absorbed equallybecause the body needs them


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Concept check

Where does the chemical digestion of proteinbegin?

Why might supplementing one amino acidreduce the absorption of other amino acids?


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Amino acid pool

Amino acid pool: amino acids available for

use in the body

From the diet or breakdown of body proteins

Used to make other proteins or chemicals (forexample: DNA, RNA, histamine, etc.)

Used to provide energy or make glucose or fatty

acids


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Amino acid pool

The amino acids in the amino acid pool come from _________ and ___________.


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Genes contain instructions for proteins

Each gene contains the instructions for oneRNA molecule. RNA is transcribed (re-written)from DNA.

Messenger RNA (mRNA) molecules exit thenucleus and contain instructions for the orderofamino acids in a protein. The nucleotideinstructions in DNA and RNA are translated to

the amino acid language ofproteins.

P i

h i


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Protein synthesis


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Genes contain instructions for proteins

S h i i i


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Synthesizing proteins

The instructions for making proteins are contained in the nucleus of the cell in

stretches of DNA called genes.

When a protein is synhesis begins, and the information contained in the gene

is used to make the necessary protein.


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Gene mutations

Changes in gene sequence can change thesequence of the amino acids in a protein

Changes in (amino acid) sequence can change howa protein folds and change its structure

Changes in protein structure can change proteinfunction

+ - -

i kl ll i


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sickle-cell anemia


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Gene regulation

All cells contain the same DNA. During development,

some genes are turned on and others are turned off so

cells can carry out specific functions.

For example, insulin-producing cells turn on the insulin gene

and turn off muscle contraction genes.

Chemicals can turn genes on and off.

For example, high iron turns on the ferritin gene to make more

ferritin which is needed for iron storage.


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Concept check

Building blocks of proteins are:

a) nucleotides

b) amino acids

c) DNA and RNA

d) codons


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Concept check

Amino acids are linked together:

a) During translation

b) In the nucleus

c) When DNA is made from RNA

d) During transcription


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Protein functions

Speed up chemical reactions

Structures

Some chemical signals (for example, hormones)

Transportation of substances

Movement of muscles

Immunity (for example, antibodies)

Blood clotting

Fluid balance


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Body Proteins Provide Many Functions

Proteins provide structure

The most visible example is the protein in muscles

Skin and hair are also composed largely of protein

The most abundant protein in the body is collagen; it holds cells togetherand forms the protein framework of bones and teeth

Enzyme proteins speed up metabolic reactions

Enzymes are proteins that speed up metabolic reactions but are notused up or destroyed in the process

Enzymes that function in the body are made by the body and thereforedo not need to be consumed in the diet

d i id i


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Body Proteins Provide Many Functions

Proteins transport molecules throughout our body

Transport proteins act as shuttles. In the blood they carry substancesfrom one organ to another. For example, hemoglobin, the protein thatgives red blood cells their red color, picks up oxygen in the lungs andtransports it to other organs of the body

Proteins protect us from injury and infection Skin, which is made up primarily of protein, is the first barrier against

infection and injury

Proteins help us move

Some hormones are proteins

Proteins help regulate fluid balance

Proteins help regulate acidity

Protein functions


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Protein functions


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Protein functions


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Using proteins

Amino acids from the diet are used to make

proteins and nitrogen-containing molecules

Extra amino acids cannot be stored

Extra amino acids are used for energy or

stored as fat


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Using proteins for energy

When we do not consume enough calories to

meet needs, body proteins are broken down

since amino acids are not stored

Deamination removes amino group (NH2) Produces urea which is excreted in urine

Carbon, hydrogen, and oxygen can be broken

down to produce ATP or used to make glucoseor fatty acids



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h k


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Concept check

Why does protein synthesis stop when the

supply of an amino acid is limited?

How does the body know in what order toassemble the amino acids when making a

protein?

When is protein used as an energy source?

P i l i i (P M)


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Protein-energy malnutrition (PEM)

Loss of fat and muscle and decreasedimmunity from long-term protein and calorie

deficiencies

Types:

Kwashiorkor: pure protein deficiency

Marasmus: overall energy deficiency

Protein energy malnutrition (PEM)


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Protein-energy malnutrition (PEM)

P i


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Protein excess

Increased urea output

Increased demands on the kidneys

Increased loss of water from the body

Possible increased loss of calcium Increased risk of kidney stones

Hi h i di


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High-protein diets

Usually:

high in animal proteins with high saturated fat

and cholesterol and low in fiber

low in grains, fruits, and vegetables

high in calories and fat

Increased risk of heart disease, cancer,

obesity, and diabetes

P i ll i


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Protein allergies

When a protein is absorbed intact, the

immune system can recognize it as an

antigen and start cellular reactions

The second time immune system detects thatsame allergen (allergy-causing antigen), there

is an allergic reaction

Major food allergens: milk, eggs, peanuts,tree nuts, fish, shellfish, soy, and wheat

P i f d l b l


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Protein on food labels

F d i i i i


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Food sensitivities

Do not involve the immune system

Trigger various symptoms after consumption

Examples:

MSG symptom complex or Chinese restaurant

syndrome

Gluten intolerance or Celiac disease

Consumption of gluten in rye, wheat or barley triggers anautoimmune reaction against villi in the small intestines

C h k


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Concept check

What are consequences of low or high protein

diets?

Ni b l


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Nitrogen balance

Nitrogen intake equals nitrogen loss

Maintaining body protein and weight

Negative nitrogen balance:

more nitrogen lost than consumed

From illness, injury, or decreased consumption

Positive nitrogen balance:

more nitrogen consumed than lost

From growth, pregnancy, or weight training

Nitrogen balance


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Nitrogen balance

P t i d d d il ll


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Protein recommended daily allowanceDuring the first year of life, growth is rapid, so a large amount

of protein is required per unit of body weight. As growth rate

slows, requirements per unit of body weight decrease butcontinue to be greater than adult requirements until age 19.

What is the RDA for a 2-year-old child who weighs 14

kilograms?

a)14 g/day

b)15.4 g/day

c)11.2 g/day

d)21 g/day

P t i d d d il ll


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Protein recommended daily allowance

0.8 g/kilogram of body weight for adults

With more weight, more protein is needed for

maintenance and repair

70 kg (154 lb) adult = 56 g of protein/day Average consumption = 70 g of protein/day

Higher needs in infants, during pregnancy

and lactation (breast feeding), after injury,

and in endurance athletes

Pregnant/lactating women: add 25 g of protein/day

C l l t


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Calculate

100 pound adult

weight in kilograms equals weight in pounds

x0.45 kg/lb

Protein RDA = 0.8 g/kilogram of body weight

How much protein does this person need?

Pr t i i t k i thl t


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Protein intake in athletes

Protein supplements


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Protein supplementsProtein and amino acid supplemens

Protein and amino acid supplements are rarely needed to meet protein needs. Nonetheless,

supplements are marketed to boost total protein intake, to add individual amino acids, and

to provide enzyme activity

Protein dietary recommendations


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Protein dietary recommendations

Acceptable Macronutrient Distribution Rangefor protein:10% to 35% of calories

Dietary Guidelines 2010 recommend that we

choose a variety of protein foods, includingseafood, lean meat and poultry, eggs, beans,

soy products, and unsalted nuts and seeds

Protein quality


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Protein quality

High-quality, or complete dietary, proteins

Contain all amino acids to meet bodys needs

More easily digested

Animal proteins and soy

Incomplete proteins

Lower in one or more essential amino acids Most plant proteins

Use complementary proteins

Complementary proteins


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Complementary proteins

Choosing healthy proteins


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g y p

Debate


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Debate

Should you switch to soy?

What should I eat?


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What should I eat?

Get protein without too much saturated fat

Eat both animal and plant proteins

Go with beans

What are some menu items

you could consume?

Vegetarian diets


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Vegetarian diets

Reasons to be vegetarian: Limited land and/or resources

Health

Religion Personal ethics

Environmental concerns

Benefits: lower cost and healthier

Risks: amino acid, mineral, and B vitamin

deficiency

Well-Planned Vegetarian Diets Are Healthy


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Well Planned Vegetarian Diets Are Healthy

You dont need to eat any animal foods to stay healthy.By combining plant proteins containing different limitingamino acids you can get the right combinations ofamino acids to meet your protein needs

Vegetarian diets include a variety of eating patterns

Traditionally, vegetarianism is defined as abstinence frommeat, fish, and fowl, but the term has come to mean manydifferent things

Well-Planned Vegetarian Diets Are Healthy


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Well Planned Vegetarian Diets Are Healthy

Vegetarian diets can have nutritional, health, and economicadvantages

Vegetarians have been shown to have lower risks for obesity,diabetes, cardiovascular disease, high blood pressure, and sometypes of cancer

Despite the health and economic benefits of vegetarian diets,nutrient deficiencies can be a problem, particularly for peopleconsuming vegan diets

Vegetarian pyramids help you choose a meatless diet

Types of vegetarian diets


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Types of vegetarian diets

Semivegetarian: Excludes red meat but may includefish and poultry, as well as dairy products and eggs

Pescetarian: Excludes all animal flesh except fish

Lacto-ovo vegetarian: Excludes all animal flesh but

includes eggs and dairy products Lacto vegetarian: Excludes animal flesh and eggs but

includes dairy products

Vegan: Excludes all food of animal origin

Meeting dietary needs with a vegan diet


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Concept check


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Concept check

How can nitrogen balance be maintained?

What are benefits and risks of consuming a

plant-based diet?

How can vegetarians avoid nutrient

deficiencies?

Think critically


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Think critically

Sickle cell anemia is an inherited disease caused by anabnormality in the gene for the protein hemoglobin. It

causes red blood cells to take on a sickle shape.

Sickle cell hemoglobin differs from normal

hemoglobin by one amino acid. Why might this

difference change the shape of the hemoglobin?

Do you think sickle-shaped red blood cells can

travel easily through narrow capillaries?

How might this disorder affect the ability to get

oxygen to the bodys cells?

What are similarities and differences


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What are similarities and differences

between:

Proteins and amino acids?

Chromsomes and genes?

DNA and mRNA? Plant and animal proteins?

Kwashiorkor and marasmus?

Vegetarian and vegan diets?

Applications


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Applications

What advice could you give to a loved onabout protein consumption to decrease

disease risk?

Nutrition in the news


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Nutrition in the news

Atkins diets

Protein supplements for weight lifters

Checking student learning outcomes


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Checking student learning outcomes

How do proteins contribute to health anddisease?

What advice would you give to a loved one

about protein consumption?

Ch06 Proteins

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