B.Sc. Biochem II Biomolecule I U 3.2 Classification of Protein & Denaturation

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CLASSIFICATION OF PROTEINS & DENATURATION Course: B.Sc.(Biochem) II Subject: Biomolecules I Unit 3.2

Transcript of B.Sc. Biochem II Biomolecule I U 3.2 Classification of Protein & Denaturation

Page 1: B.Sc. Biochem II Biomolecule I U 3.2 Classification of Protein & Denaturation

CLASSIFICATION OF PROTEINS &

DENATURATION

Course: B.Sc.(Biochem) II

Subject: Biomolecules I

Unit 3.2

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PROTEIN CAN BE CLASSIFIED BY:

Structure

Biological function

Shape and solubility

Composition

Nutritional basis

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CLASSIFICATION

BY

BIOLOGICAL FUNCTION

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ENZYMES

Those proteins which are highly specialized in

their function with catalytic activity.

These proteins regulate almost all biological

reactions going on inside all living cells.

There are about 2000 different enzymes has

been recognized; each capable of catalyzing a

different kind of biochemical reaction.

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TRANSPORT PROTEINS

are those proteins which help in transportation of

life sustaining chemicals vital gases and nutrients.

Carry essential substances throughout the body.

Example:

- Haemoglobin is a globular protein present in RBC of

blood can binds with oxygen when blood passes

though longs and distributes oxygen through out

the body cells to affect cellular respiration.

- Blood plasma contains lipoprotein which carries

lipids from the liver to other organs.

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STORAGE PROTEINS

are those stored inside the cells or tissue as

reserved food and can be mobilized at the time of

nutrient requirement to provide energy.

Store nutrients.

Example:

- Casein stores protein in milk.

- Ferritin stores iron in the spleen and liver.

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CONTRACTILE/MOTILE PROTEINS

Move muscles.

the ability to contract to change the shape or to

move about.

These proteins includes. Actin and myosin; which

are present in form of filamentous protein in muscle

cells for functioning in the contractile systems.

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STRUCTURAL PROTEINS

This type of protein form major component of

tendons, cartilages and bones.

These are fibrous proteins named collagen.

Ligaments are contains special structural protein

capable of stretching in two dimensions called as

elastin.

Hairs finger nails, feathers of birds consists of tough

insoluble protein named keratin.

Major component of silk fibers, threads of spider

web contain structural protein named fibroin.

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REGULATORY PROTEIN

Some proteins help to regulate cellular or

physiological activity. Among them are many

hormones, such as insulin; which is a regulatory

protein formed in pancreatic tissue help to regulate

the blood sugar level.

Growth hormones of pituitary and parathyroid

hormones regulate Ca++ and phosphate transport

in body. Other proteins called repressors regulate

biosynthesis of enzymes.

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OTHER FUNCTIONAL PROTEINS

There are number of proteins whose functions are

not yet specified and are rather exotic. These

includes –

Monelin: - A protein of an African plant has an

intensely sweet taste and used as non toxic food

sweetener for human use.

Antifreeeze: A protein present in blood plasma of

Antarctic fisher which protect their blood freezing in

ice cold water.

Resillin: A type of protein present in wing hinges of

some insects with elastic properties.

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CLASSIFICATION

BY

SHAPE & SOLUBILITY

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FIBROUS PROTEINS these proteins have a rod like structure. They are

not soluble in water.

(a) These are made up of polypeptide chain thatare parallel to the axis & are held together by stronghydrogen and disulphide bonds.(b) They can be stretched & contracted likethread.

Examples:

-Collagen

-Keratin

-Fibrinogen

-Muscle protein

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GLOBULAR PROTEINS these proteins more or

less spherical in nature.

Due to their distribution of

amino acids (hydrophobic

inside, hydrophillic

outside) they are very

soluble in aqueous

solution.

Examples

Myoglobin, albumin,

globulin, casein,

haemoglobin, all of the

enzymes, and protein

hormones.1

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CLASSIFICATION

BY

COMPOSITION

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SIMPLE PROTEINS are those which on hydrolysis yield only amino

acids and no other major organic or inorganic

hydrolysis products. They usually contain about

50% carbon,7% hydrogen, 23% oxygen, 16%

nitrogen and 0–3% sulphur.

Example:

-Egg (albumin)

-Serum (globulins)

-Wheat (Glutelin)

-Rice (Coryzenin)

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CONJUGATED PROTEINS

are those which on hydrolysis yield not only amino

acids but also organic or inorganic components.

The non-amino acid part of a conjugated protein is

called prosthetic group.

Conjugated proteins are classified on the basis of

the chemical nature of their prosthetic groups.

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NUTRITIONAL BASIS

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COMPLETE PROTEINS A complete protein contains an adequate amount of

all of the essential amino acids that should be

incorporated into a diet.

Some protein contains all the amino acids needed

to build new proteins, which generally come from

animal and fish products. A complete protein must

not lack even one essential amino acid in order to

be considered complete.

Sources: The following foods are examples of

complete proteins, which need not be combined

with any other food to provide adequate protein:

Meat, Fish, Poultry, Cheese, Eggs, Yogurt, Milk

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INCOMPLETE PROTEINS

An incomplete protein is any protein that lacks one

or more essential amino acids in correct

proportions. These can also be referred to as partial

proteins.

Even if the protein contains all the essential amino

acids, they must be in equal proportions in order to

be considered complete. If not, the protein is

considered incomplete.

Sources of Incomplete Proteins: Grains, Nuts,

Beans, Seeds, Peas, Corn

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COMBINING INCOMPLETE PROTEINS TO

CREATE COMPLETE PROTEINS

By combining foods from two or more incomplete

proteins, a complete protein can be created.

The amino acids that may be missing from one type

of food can be compensated by adding a protein

that contains that missing amino acid.

When eaten in combination at the same meal, you

are providing your body with all the essential amino

acids it requires. These are considered

complementary proteins when they are combined to

compensate for each other's lack of amino acids.

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SAMPLES OF COMPLEMENTARY

PROTEINS

create a complete protein in one meal include:

Grains with Legumes - sample meal: lentils and rice

with yellow peppers.

Nuts with Legumes - sample meal: black bean and

peanut salad.

Grains with Dairy - sample meal: white cheddar and

whole wheat pasta.

Dairy with Seeds - sample meal: yogurt mixed with

sesame and flax seeds.

Legumes with Seeds - sample meal: spinach salad

with sesame seed and almond salad dressing.

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CHEMICAL PROPERTIES

Denaturation of Proteins

Denaturation is a process in

which proteins or nucleic acids lose the quaternary

structure, tertiary structure and secondary

structure which is present in their native state, by

application of some external stress or compound

such as a strong acid or base, a

concentrated inorganic salt, an organic solvent

(e.g., alcohol or chloroform), radiation or heat.

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Denaturation occurs because the bonding interactions

responsible for the secondary structure (hydrogen

bonds to amides) and tertiary structure are disrupted.

In tertiary structure there are four types of bonding

interactions between "side chains" including: hydrogen

bonding, salt bridges, disulfide bonds, and non-polar

hydrophobic interactions. which may be disrupted.

Therefore, a variety of reagents and conditions can

cause denaturation. The most common observation in

the denaturation process is the precipitation or

coagulation of the protein.

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HEAT

Heat can be used to disrupt hydrogen bonds and

non-polar hydrophobic interactions. This occurs

because heat increases the kinetic energy and

causes the molecules to vibrate so rapidly and

violently that the bonds are disrupted. The proteins

in eggs denature and coagulate during cooking.

Other foods are cooked to denature the proteins to

make it easier for enzymes to digest them. Medical

supplies and instruments are sterilized by heating

to denature proteins in bacteria and thus destroy

the bacteria.

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ALCOHOL DISRUPTS HYDROGEN BONDING:

Hydrogen bonding occurs between amide groups in

the secondary protein structure. Hydrogen bonding between

"side chains" occurs in tertiary protein structure in a variety of

amino acid combinations. All of these are disrupted by the

addition of another alcohol.

A 70% alcohol solution is used as a disinfectant on the skin.

This concentration of alcohol is able to penetrate the bacterial

cell wall and denature the proteins and enzymes inside of the

cell. A 95% alcohol solution merely coagulates the protein on

the outside of the cell wall and prevents any alcohol from

entering the cell. Alcohol denatures proteins by disrupting the

side chain intramolecular hydrogen bonding. New hydrogen

bonds are formed instead between the new alcohol molecule

and the protein side chains.

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ACIDS AND BASES DISRUPT SALT BRIDGES:

Salt bridges result from the neutralization of an

acid and amine on side chains. The final interaction

is ionic between the positive ammonium group and

the negative acid group. Any combination of the

various acidic or amine amino acid side chains will

have this effect.

The denaturation reaction on the salt bridge by the

addition of an acid results in a further straightening

effect on the protein chain as shown in the graphic

on the left.

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HEAVY METAL SALTS

Heavy metal salts act to denature proteins in much the same

manner as acids and bases. Heavy metal salts usually

contain Hg+2, Pb+2, Ag+1 Tl+1, Cd+2 and other metals with high

atomic weights. Since salts are ionic they disrupt salt bridges in

proteins. The reaction of a heavy metal salt with a protein

usually leads to an insoluble metal protein salt.

This reaction is used for its disinfectant properties in external

applications. For example AgNO3 is used to prevent gonorrhea

infections in the eyes of new born infants. Silver nitrate is also

used in the treatment of nose and throat infections, as well as

to cauterize wounds.

Mercury salts administered as Mercurochrome or Merthiolate

have similar properties in preventing infections in wounds.

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Acids

Acidic protein denaturants include:

Acetic acid[8]

Trichloroacetic acid 12% in water

Sulfosalicylic acid

Solvents

Most organic solvents are denaturing, including:

Ethanol

Methanol

Cross-linking reagents

Cross-linking agents for proteins include:[citation needed]

Formaldehyde

Glutaraldehyde

Chaotropic agents

Chaotropic agents include:

Urea 6 – 8 mol/l

Guanidinium chloride 6 mol/l

Lithium perchlorate 4.5 mol/l

Disulfide bond reducers[edit]

Agents that break disulfide bonds by reduction include:[citation

needed]

2-Mercaptoethanol

Dithiothreitol

TCEP (tris(2-carboxyethyl)phosphine)

Other

Picric acid

Radiation

Temperature

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Example of denaturation that occurs in our

living:

1. Denaturation of human hair

The extent to which fatty acid oxygenases are

activated in the normal epidermis is not known

2. In cooking eggs

cooking eggs turns them from runny to solid

cooking food makes it more digestible.

3. Milk forms a solid curd on standing

· bacteria in milk grows

· forms lactic acid

· protonates carboxylate groups

· becomes isoelectric

· coagulates into a solid curd

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REFERENCES:

Image 1: http://postimg.org/image/6m1jvvgbj/

Image 2: http://postimg.org/image/quoxhlfmn/

Books:

1. Biochemistry, U. Satyanarayan, Elsevier India

publication

2. Principles of Biochemistry by Lehninger

3. Harper’s Illustrated Biochemistry by Robert,

Murray, Hranner, Mayes and Rodwell