Protein in diet

What is protein?

The Proteins are derived from Greek word Proteions. They are compounds obtained by combination of different Amino Acids. Chemically, proteins are polymers of molecules units called Amino acids. i.e. Amino acids are "building blocks" Of proteins. The proteins have high molecular weight ranging from 5000 to many millions.

Biological importance of Proteins:

Proteins play vital role in all biological process.

1) All enzymes are proteins, but all proteins are not enzymes. Enzymes act as a catalyst for biological processes.

2) Some Harmones are proteins. Harmones plays important role in Regulation and control the biological process.
e.g. Insulin is the harmone which control sugar level.

3) Haemoglobin is protein and it is involved in transport of oxygen. From lungs to different parts of cell.

4) Proteins are major components of muscles.

5) Some proteins act as structural materials of living organism.
e.g. skin, bone, teeth, hair etc.

6) Some proteins act as a antibodies which provide protection against disease.

7) Proteins plays important role in generation and transmission of nerve impulses.

Laboratory Synthetic of Proteins:

Although it is possible to synthesize proteins in the laboratory by condesing alpha-amino acids with each other, obtaining the desired protein in good yield is always complicated as number of permutation combination of condesation of -NH2 and -COOH groups would lead to mixture of different peptides/ proteins.

Let us consider the synthesis of only a dipeptide such as Alanine -Phenyl alanine (Ala-Phe);with Alanine at N terminal and phenyl alanine at C-terminal.

Classification of Proteins:

A) Classification of proteins based on it's chemical composition.

a) Simple proteins:

These proteins on hydrosis gives only alpha-amino acids.
Examples: Keratin, Albumin, Globulin etc.

* Keratin: keratins are the proteins of hair, wool, quills, hoofs, nails etc. They are derived from ectoderm.

* Albumin: Albumins are readily soluble in water and coagulation by heat. This is a large group of which egg white (ovalbumin) and serum albumin are examples.
Albumins may be precipitated from solution at high concentration, this process called as "salting out".

*Globulin: Globulins are Insoluble or sparingly soluble in water, but their solubility is greatly increased by the addition of neutral salts such as Nacl.

These proteins are coagulated by heat.

b) Conjugated proteins:

These proteins on hydrosis gives amino acids along with some Non-proteinous part called as prosthetic group. The term Prosthetic group is generally used to designate the non-amino acid moiety.

e.g. 1) Glycoproteins: These proteins contain carbohydrates as a prosthetic group.

2) Lipoproteins: These are water soluble proteins containing lipid as a prosthetic group.

3) Mucoproteins: Mucoids as a prosthetic group.

4) Nucleoproteins: These proteins contains nucleic acid as a prosthetic group.

5) Chromoproteins: These are compounds of protein with coloured pigment.

6) Flavoproteins: Flavin component (FAN or FAD) is prosthetic group.

C) Derived proteins:

These are the Intermediate degradation product obtained by the action of acid or base on proteins.
protean,metaprotein, protease, polypeptide, lower peptide are derived proteins.

Classification of proteins based on structure:

On the basis of structure, proteins are classified as:

a) Fibrous proteins:

These insoluble animal protein, highly resistant to degestion by proteolytic enzymes. These are made up of long filamentaous chain held together by cross link and H-bonding.

* Collagen : These are insoluble in water and resistant to animal digestive enzymes.

* Myosin: This is the major component of muscle.

*Ossein: It is found in bones and teeth.

*Elastin: It is present in tendon, arteries and other elastic tissue.

b) Globular proteins:

These proteins are obtained by extensive folding of polypeptide chain to form compact structure. These are spherical or avoid in shape because of presence of peptide chain which are folded in compact manner. Such aggregates held together in three-dimensional structure by weak non-covalent bond. They are soluble in water as well as in organic solvent. Most of the globular proteins function as a enzyme.

e.g.
1) Albumin: These are water soluble protein and coagulated by heat.
2) Globulin.

3) Myoglobin.

4) Histones: These are basic proteins and soluble in water. The globin present in haemoglobin is a histone.

5) Glutelin: Insoluble in distilled water or alcohol but soluble in dilute acid or base solutions. Found in plant seeds.

Classification of proteins based on its function :

1) Transport proteins:

These proteins present in blood plasma and carry specific molecules or ions from one organ to another.
e.g. Lipoproteins : This present in blood plasma which carry lipids from Liver to another organ.

2) Nutrient or storage Proteins:

These proteins present in seed of plant which is required for growth of germinating seedling.
1) Seed proteins of wheat, rice, corn.
2) Ovalbumin: Egg white part.
3) Casein: Proteins in milk.
4) Ferritin: This is present in bacteria and in plant and animal tissue which stores iron.

3) Contratile or motile proteins:

These protein used to contract to change shape or to move about.
1) Actin: function in contractile system of skeletal muscle.
2) Tubulin: These are the proteins from which microtubules are built.

4) Structural proteins :

These proteins serve as a supporting filament to give biological structure Strength or protection.
Examples: Collagen, Keratin etc.

5) Defense proteins:

These proteins protect organism from injury.
Example: Fibrinogen and Thrombin are blood clotting proteins that prevents loss of blood when vascular system is injured.

6) Regulatory proteins:

These proteins help to regulate cellular or physiological activity.
Example: Insulin- which regulate sugar metabolism and growth of hormone of pituitary.

Structural organization of proteins:

Structure of Protein

A) Primary structure of proteins:

Primary structure of protein

* Primary structure of proteins refers to the linear sequence of amino acids in the polypeptide chain.

* The amino acids are linked with each other by peptide bonds only. Thus the primary structure is the complete description of covalent connections of a proteins.

* In 1953 Frederick Sanger elucidated the primary structure of proteins have N-terminal and C-terminal.

* The sequence of primary structure is characteristics of individual proteins if sequence of primary structure change. The protein produced is different.

So, this is all about the Primary structure of Protein.

B) Secondary structure:

Secondary structure of Protein

* Secondary structure of proteins is formed by intra or intermolecular H-bonding.

* Secondary structure of protein are arranged in coiled or folding manner.

In some cases the protein chains are arranged to form a bete-pleated structure. The alpha-helix and beta-pleated structure represent the secondary structure.

C) Tertiary structure:

Tertiary structure of Protein

The alpha-helical chains are folded or bent at number of points to produce a complex structure of the protein. The tertiary structure gives the typical shape to the protein. So, this is the Tertiary structure of Protein.

D) Quaternary structure:

Quaternary structure of Protein

Some proteins contain more than one chains held together. The way in which more than one protein chains are held together gives us the quaternary structure of the protein.

Protein subunits are linked in quaternary structures with hydrogen bonding, ionic bonding. Bonding of hydrophobic patches on adjacent subunits; that is really a state forced by the exclusionary nature of hydrogen bonding in the surrounding aqueous medium. That means water binding to itself and forcing everything else into different regions.

So, this is all about Proteins , structures of proteins, classification of Proteins etc