ProteinProtein

Chapter 17Chapter 17

What is Protein?What is Protein?

Protein molecules are very large and Protein molecules are very large and complex. Made up of:complex. Made up of:

– Hydrogen, carbon, oxygen ,nitrogen and Hydrogen, carbon, oxygen ,nitrogen and sometimes other elementssometimes other elements

– Because of protein large size, protein molecules Because of protein large size, protein molecules are often called macromoleculeare often called macromolecule

MacromoleculeMacromolecule = large molecule containing = large molecule containing many atoms.many atoms.

– Nitrogen is a crucial part of proteinNitrogen is a crucial part of protein

Nitrogen is the site of the chemical bond that Nitrogen is the site of the chemical bond that gives proteins their variety and versatilitygives proteins their variety and versatility

Structure of ProteinStructure of ProteinProtein is made of chains of amino Protein is made of chains of amino acids.acids.– Amino AcidsAmino Acids = type of organic acid. = type of organic acid.

– Organic acids are molecules that contain a Organic acids are molecules that contain a carboxyl group, plus the amino acids also contain carboxyl group, plus the amino acids also contain an amine group.an amine group.

– Amine groupAmine group = composed of two atoms of = composed of two atoms of hydrogen and one atom of nitrogen.hydrogen and one atom of nitrogen.

– (Look on page 258, figure 17-1, both carboxyl (Look on page 258, figure 17-1, both carboxyl group and the amine group are attached to a group and the amine group are attached to a central carbon.)central carbon.)

– With four bonds needed and one is left open, this With four bonds needed and one is left open, this is what makes one amino acid different from is what makes one amino acid different from another.another.

Peptide BondsPeptide BondsPeptide bondsPeptide bonds = bonds between = bonds between the nitrogen of one amino acid and the nitrogen of one amino acid and the carbon of a second amino acid. the carbon of a second amino acid. (example is on page 258, figure 17-3)(example is on page 258, figure 17-3)

Through peptide bonds, amino acids chain Through peptide bonds, amino acids chain together, creating a polypeptide.together, creating a polypeptide.PolypeptidePolypeptide = single protein molecule = single protein molecule containing then or more amino acids linked containing then or more amino acids linked in peptide chainsin peptide chains

– Peptide bonds hold chains of amino acids Peptide bonds hold chains of amino acids together, that are called helixes (ex. page 259, together, that are called helixes (ex. page 259, figure 17-4)figure 17-4)

Protein Structure and FunctionProtein Structure and Function

Protein’s shape determine its Protein’s shape determine its functionfunction

Protein molecules that form rope-like fibers Protein molecules that form rope-like fibers are called fibrous protein ex is collagen and are called fibrous protein ex is collagen and elastin elastin

Protein molecules that can be compared to a Protein molecules that can be compared to a ball of steel wool are called globular proteinsball of steel wool are called globular proteins

– The shape makes them convenient carriers ex The shape makes them convenient carriers ex hemoglobin (transports oxygen in the blood)hemoglobin (transports oxygen in the blood)

Denaturation of ProteinDenaturation of ProteinDenaturationDenaturation = this process changes the = this process changes the shape of a protein molecule without shape of a protein molecule without breaking its peptide bondsbreaking its peptide bonds

As the molecule unfolds, some of the protein’s As the molecule unfolds, some of the protein’s original properties are diminished or lost.original properties are diminished or lost.This change is unique to protein and because each This change is unique to protein and because each protein is unique the process varies from one protein is unique the process varies from one molecule to the next.molecule to the next.Denaturation in the first step in the process of Denaturation in the first step in the process of coagulationcoagulationCoagulationCoagulation = changes a liquid into a soft, semisolid = changes a liquid into a soft, semisolid clot or solid mass. (look pg. 260, figure 17-6)clot or solid mass. (look pg. 260, figure 17-6)

– Ex is scrambled eggs. Beating the egg denatures its Ex is scrambled eggs. Beating the egg denatures its protein. The protein coagulates as the egg cooks.protein. The protein coagulates as the egg cooks.

Other Means of DenaturationOther Means of DenaturationHeat is the most common agent in Heat is the most common agent in denaturing protein.denaturing protein.

The temperature is significant, the degree of The temperature is significant, the degree of denaturation increase 600 times for every 10°C.denaturation increase 600 times for every 10°C.

Protein molecules may unfold in reaction Protein molecules may unfold in reaction to the following:to the following:

Freezing, pressure, and sound wavesFreezing, pressure, and sound wavesMechanical treatment, such as beating eggs and Mechanical treatment, such as beating eggs and kneading breadkneading breadVery high or very low pH. (adding lemon juice for Very high or very low pH. (adding lemon juice for example can sour milk, causing the milk to separate example can sour milk, causing the milk to separate from the liquid – forming curds and whey)from the liquid – forming curds and whey)Certain metal ionsCertain metal ions

Protein in EggsProtein in EggsEggsEggs

Complex biological system, containing almost every Complex biological system, containing almost every vitamin and mineral you need. All that lacks is vit. C vitamin and mineral you need. All that lacks is vit. C and calcium which is found in the egg shelland calcium which is found in the egg shell

Look on pg. 262, figure 17-7 for a diagram of an eggLook on pg. 262, figure 17-7 for a diagram of an egg– AlbumenAlbumen = egg white – substance makes up 54% of = egg white – substance makes up 54% of

the inner contents of an eggthe inner contents of an egg– ChalazaChalaza = a twisted, ropelike structure that keeps the = a twisted, ropelike structure that keeps the

egg yolk centeredegg yolk centered– Egg Yolk – main component of the yolk include the Egg Yolk – main component of the yolk include the

globular protein livetin and both high-and-low-density globular protein livetin and both high-and-low-density lipoproteinslipoproteins

StorageStorage– Do not exposed eggs to light and temperature changesDo not exposed eggs to light and temperature changes

Eggs lose quality as compounds in the egg white Eggs lose quality as compounds in the egg white break down, forming waterbreak down, forming water

Protein in MeatProtein in Meat

Muscle tissue, the lean part of meat, Muscle tissue, the lean part of meat, is about 15-20% proteinis about 15-20% protein– Other components include: water, fat Other components include: water, fat

and mineralsand minerals– Muscle is composed of fibrous proteins Muscle is composed of fibrous proteins

called actin and myosin. These proteins called actin and myosin. These proteins form bundles of fiber, which are held form bundles of fiber, which are held together by connective tissue made of together by connective tissue made of collagen and elastincollagen and elastin

Protein in Fish, Nuts and LegumesProtein in Fish, Nuts and LegumesFishFish– Shorter segmented muscle fibers are layered Shorter segmented muscle fibers are layered

between thin sheets of connective tissue. This between thin sheets of connective tissue. This is why some books say fish is cooked when you is why some books say fish is cooked when you can “flake with a fork”can “flake with a fork”

– Far less connective tissue than meat, it’s also a Far less connective tissue than meat, it’s also a type that liquefies easilytype that liquefies easily

Nuts and LegumesNuts and Legumes– Cholesterol free, but fat content rangesCholesterol free, but fat content ranges– Soybeans are excellent source of protein, Soybeans are excellent source of protein,

they’re composed of 40% protein, high in fiber they’re composed of 40% protein, high in fiber and polyunsaturated fatty acids. Soybeans and polyunsaturated fatty acids. Soybeans have also been associated with reducing the have also been associated with reducing the risk of coronary heart diseaserisk of coronary heart disease

Protein in CookingProtein in CookingEmulsifiersEmulsifiers

Certain proteins contain amino acids that our polar. Certain proteins contain amino acids that our polar. One end is attracted to water (forming a hydrogen One end is attracted to water (forming a hydrogen bond), the other end avoids water and bonds with oil. bond), the other end avoids water and bonds with oil. This is why an egg can emulsify oil and lemon juice This is why an egg can emulsify oil and lemon juice

FoamsFoamsFoamFoam = air bubbles incorporated and trapped in a = air bubbles incorporated and trapped in a protein film by whippingprotein film by whipping

– Foam begins when a protein-containing liquid (egg Foam begins when a protein-containing liquid (egg whites or cream) are whipped, introducing air and whites or cream) are whipped, introducing air and denatures the protein moleculesdenatures the protein molecules

– Fats can be trouble for foams, they keep protein Fats can be trouble for foams, they keep protein molecules from bonding with each other, making the molecules from bonding with each other, making the end product wateryend product watery

Protein in Cooking ContinuedProtein in Cooking ContinuedGelatinGelatin

Used to set desserts and thicken meat sauces in Used to set desserts and thicken meat sauces in animal proteinanimal proteinMade by using heat and water to hydrolyze the Made by using heat and water to hydrolyze the collagen on the inner layer of hides and bonescollagen on the inner layer of hides and bonesGelatin can bind 100 times its weigh in waterGelatin can bind 100 times its weigh in water

GlutenGlutenGlutenGluten = an elastic substance formed by mixing = an elastic substance formed by mixing water with the proteins found in wheatwater with the proteins found in wheatGluten includes both fibrous and globular proteins, Gluten includes both fibrous and globular proteins, making the reactions between the water and proteins making the reactions between the water and proteins both stretch and springyboth stretch and springyGluten is developed as dough is kneaded, denaturing Gluten is developed as dough is kneaded, denaturing the protein moleculesthe protein molecules

Protein in the BodyProtein in the BodyDuring digestion, proteins are denatured by During digestion, proteins are denatured by hydrochloric acid in the stomach, making the hydrochloric acid in the stomach, making the peptide bonds easier for enzymes to break.peptide bonds easier for enzymes to break.

Most proteins enter the bloodstream as amino Most proteins enter the bloodstream as amino acids (the body creates ALL of its proteins from acids (the body creates ALL of its proteins from 20 different amino acids)20 different amino acids)

Functions of Body ProteinsFunctions of Body Proteins– Structural protein is needed by every cell in the bodyStructural protein is needed by every cell in the body– New growth requires a continuous supply of protein to New growth requires a continuous supply of protein to

replace and repair cellsreplace and repair cells– Some proteins pick up, deliver and stores nutrients in Some proteins pick up, deliver and stores nutrients in

cellscells– Proteins called antibodies help you ward off diseaseProteins called antibodies help you ward off disease

AntibodiesAntibodies = very large proteins that weaken or destroy = very large proteins that weaken or destroy foreign substances in the body.foreign substances in the body.

Essential Amino AcidsEssential Amino Acids

Of the 22 amino acids the body Of the 22 amino acids the body needs to build protein, it needs to build protein, it manufactures 18 the other 9 needs manufactures 18 the other 9 needs to be digested. to be digested. Look on pg 269, figure 17-8Look on pg 269, figure 17-8

– Complete ProteinComplete Protein = a protein that contains = a protein that contains all the essential amino acids ex. ground beefall the essential amino acids ex. ground beef

– Incomplete proteinIncomplete protein = lacking one or more = lacking one or more essential amino acids, among plants only essential amino acids, among plants only soybeans provide complete proteinsoybeans provide complete protein

High-quality ProteinHigh-quality Protein = contains all the essential = contains all the essential amino acids in proportion to the body’s need for amino acids in proportion to the body’s need for themthem

Protein AllowancesProtein AllowancesThe RDA for a healthy adult is 0.8g of high-The RDA for a healthy adult is 0.8g of high-quality protein per kilogram of ideal body quality protein per kilogram of ideal body mass (take your weight in kg and multiply mass (take your weight in kg and multiply by 0.8 gives you the amount of protein by 0.8 gives you the amount of protein needed in a day (young males under 18 needed in a day (young males under 18 multiply by 0.9)multiply by 0.9)

RDA for children ages 11-14 is higher 1.0g of RDA for children ages 11-14 is higher 1.0g of protein per kg of body massprotein per kg of body mass

Most people in the US get enough proteinMost people in the US get enough protein

Look on page 270 figure 17-9 for a list of Look on page 270 figure 17-9 for a list of protein contents in certain food choices.protein contents in certain food choices.

QuestionsQuestions1.1. Why are amine groups important to Why are amine groups important to

proteins?proteins?2.2. Compare peptide bonds and hydrogen Compare peptide bonds and hydrogen

bonds in protein formation.bonds in protein formation.3.3. Describe the two basic protein shapes. Describe the two basic protein shapes.

What is the main function of each?What is the main function of each?4.4. What occurs during Denaturation?What occurs during Denaturation?5.5. Can proteins coagulate without Can proteins coagulate without

denaturation? Why or why not?denaturation? Why or why not?6.6. How does the egg yolk compare in How does the egg yolk compare in

composition to the egg white?composition to the egg white?

Questions ContinuedQuestions Continued7.7. A friend refrigerates eggs still in their carton A friend refrigerates eggs still in their carton

immediately after returning form the immediately after returning form the supermarket. Explain whether this is a good supermarket. Explain whether this is a good idea.idea.

8.8. Compare the protein structure of meat to that in Compare the protein structure of meat to that in fish.fish.

9.9. Suppose your egg whites aren’t making a very Suppose your egg whites aren’t making a very impressive foam. What might be some impressive foam. What might be some reasons?reasons?

10.10. Why is kneading the dough an important step in Why is kneading the dough an important step in making bread?making bread?

11.11. Why might injury and illness be more serious for Why might injury and illness be more serious for someone with a long-term protein deficiency?someone with a long-term protein deficiency?

12.12. Should you be concerned if your diet lacks just Should you be concerned if your diet lacks just one essential amino acid? Explain.one essential amino acid? Explain.

13.13. Can a diet of fruits, vegetables, and grains Can a diet of fruits, vegetables, and grains supply all of the essential amino acids? Explain.supply all of the essential amino acids? Explain.