CLASSIFICATION

OF

BY:MARK PHILIP Z. BESANA

PROTEIN CAN BE CLASSIFIED BY:

StructureBiological functionShape and solubilityCompositionNutritional basis

CLASSIFICATIONBY

STRUCTURE

PRIMARY STRUCTURE The primary structure of proteins is defined

as a linear sequence of amino acids joined together by peptide bonds.

Peptide bonds and disulfide bonds are responsible for maintaining the primary structure.

SECONDARY STRUCTURE

The secondary structure of a protein is defined as a local spatial structure of a certain peptide segment, that is, the relative positions of backbone atoms of this peptide segment.

H-bonds are responsible for stabilizing the secondary structure.

Repeating units of Ca-C(=O)-N(-H)-Ca constitute the backbone of peptide chain.

Six atoms, Ca-C(=O)-N(-H)-Ca, constitute a planer peptide unit.

TERTIARY STRUCTURE

The tertiary structure is defined as the three-dimensional arrangement of all atoms of a protein.

QUATERNARY STRUCTURE

The quaternary structure is defined as the spatial arrangement of multiple subunits of a protein.

These subunits are associated through H-bonds, ionic interactions, and hydrophobic interactions

CLASSIFICATIONBY

BIOLOGICAL FUNCTION

ENZYMESThose 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.

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.

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.

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.

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.

DEFENSE PROTEINS

Many proteins in body of organisms posses defending action against the invasion and attack of foreign entities or protect the body from injury.

Among these proteins special globular protein named immunoglobulin's or antibodies in vertebrate’s body is the most indispensible protein.

It synthesized by lymphocytes and they can neutralize the foreign protein produced by bacteria, virus and other harmful microbes called antigens through precipitation or glutination.

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.

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.

CLASSIFICATION BY

SHAPE & SOLUBILITY

FIBROUS PROTEINS these proteins have a rod like structure. They

are not soluble in water.

(a)    These are made up of polypeptide chain that are parallel to the axis & are held together by strong hydrogen and disulphide bonds. (b)    They can be stretched & contracted like thread. 

Examples:-Collagen-Keratin-Fibrinogen-Muscle protein

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.

MEMBRANE PROTEINS These are protein which are in association

with lipid membranes. Those membrane proteins that are

embedded in the lipid bilayer have extensive hydrophobic amino acids that interact with the non-polar environment of the bilayer interior.

Membrane proteins are not soluble in aqueous solution.

CLASSIFICATIONBY

COMPOSITION

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)

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.

NUTRITIONAL BASIS

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

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

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.

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.

PROPERTIES OF

PROTEINS

•Physical Properties•Chemical Properties

PHYSICAL PROPERTIES

contains carbon, hydrogen, oxygen, nitrogen and small amount of sulphur.

composed of amino acids that are linked together by peptide bonds 

act as catalysts, enzymes that speed up the rate of chemical reactions 

provides structural support for cells transports substances across cell membrane  provides a defense mechanism against

pathogens (antibodies)  responds to chemical stimuli  secretes hormones.

TO DETERMINE MOLECULAR NATURE

•In order to determine the nature of the molecular and ionic species that are present in aqueous solutions at different pH's, we make use of the Henderson - Hasselbalch Equation.

ISOELECTRIC POINT

the negatively and positively charged molecular species are present in equal concentration. This behavior is general for simple (difunctional) amino acids.

ELECTROPHORESIS

The distribution of charged species in a sample can be shown experimentally by observing the movement of solute molecules in an electric field, using the technique of electrophoresis.

CHEMICAL PROPERTIES

Denaturation of ProteinsDenaturation 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.

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.

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.

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.

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.

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.

Acids Acidic protein denaturants

include: Acetic acid[8]

Trichloroacetic acid 12% in water

Sulfosalicylic acidSolvents Most organic solvents are

denaturing, including: Ethanol MethanolCross-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/lDisulfide 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

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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