Protein : The word protein was coined by Berzelius in 1838 and was used by G. J. Mulder first time 1840. 15% of protoplasm is made up of protein. Average proteins contain 16% nitrogen, 50–55% carbon, oxygen 20–24%, hydrogen 7% and sulphur 0.3 – 0.5%. Iron, phosphorous, copper, calcium, and iodine are also present in small quantity.
# (1) Structure of proteins : It is due to different rearrangement of amino acids. When carboxyl group of one amino acid binded with amino group (– NH2) of another amino acid the bond is called peptide bond. A peptide may be dipeptide, tripeptide and polypeptide. The simplest protein is Insulin. According to Sanger (1953) insulin consists 51 amino acids. A protein can have up to four level of conformation.
(i) Primary structure : The primary structure is the covalent connections of a protein. It refers to linear sequence, number and nature of amino acids bonded together with peptide bonds only. e.g. ribonuclease, insulin, haemoglobin, etc.
(ii) Secondary structure : The folding of a linear polypeptide chain into specific coiled structure helix) is called secondary structure and if it is with intermolecular hydrogen bonds the structure is known as pleated sheet. helical structure is found in protein of fur, keratin of hair claws, and feathers. pleated structure is found in silk fibres.
(iii) Tertiary structure : The arrangement and interconnection of proteins into specific loops and bends is called tertiary structure of proteins. It is stabilized by hydrogen bond, ionic bond, hydrophobic bond and disulphide bonds. It is found in myoglobin (globular proteins).
(iv) Quaternary structure : It is shown by protein containing more than one peptide chain. The protein consists of identical units. It is known as homologous quaternary structure e.g. lactic dehydrogenase. If the units are dissimilar, it is called as heterogeneous quaternary structure e.g. hemoglobin which consists of two chains and two chains.
# (2) Classification of proteins : Proteins are classified on the basis of their shape, constitution and function.
On the basis of shape
(i) Fibrous protein/Scleroprotein : Insoluble in water. Animal protein resistant to proteolytic enzyme is spirally coiled thread like structure form fibres. e.g. collagen (in connective tissue), actin and myosin, keratin in hairs, claws, feathers, etc.
(ii) Globular proteins : Soluble in water. Polypeptides coiled about themselves to form oval or spherical molecules e.g. albumin insulin hormones like ACTH, oxytosin, etc.
On the basis of constituents
(i) Simple proteins : The proteins which are made up of amino acids only. e.g. albumins, globulins, prolamins, glutelins, histones, etc.
(ii) Conjugated proteins : These are complex proteins combined with characterstic non–amino acid substance called as prosthetic group. These are of following types :–
(a) Nucleoproteins : Combination of protein and nucleic acids, found in chromosomes and ribosomes. e.g. deoxyribonucleoproteins, ribonucleoproteins, etc.
(b) Mucoproteins : These are combined with large amount (more than 4%) of carbohydrates e.g. mucin.
(c) Glycoproteins : In this, carbohydrate content is less (about 2 – 3%) e.g. immunoglobulins or antibiotics.
(d) Chromoproteins : These are compounds of protein and coloured pigments. e.g. haemoglobin, cytochrome, etc.
(e) Lipoproteins : These are water soluble proteins and contain lipids. e.g. cholesterol and serum lipoproteins.
(f) Metalloprotein : These are metal binding proteins, AB1–globin known as transferring is capable of combining with iron, zinc and copper e.g. chlorophyll.
(g) Phosphoprotein : They composed of protein and phosphate e.g. casein (milk) and vitellin (egg).
# (iii) Derived proteins : When proteins are hydrolysed by acids, alkalies or enzymes, the degredation products obtained from them are called derived proteins. On the basis of progressive cleavage, derived proteins are classified as primary proteoses, secondary proteoses, peptones, polypeptides, amino acids, etc.
On the basis of nature of molecules
(i) Acidic proteins : They exist as anion and include acidic amino acids. e.g. blood groups.
(ii) Basic proteins : They exist as cations and rich in basic amino acids e.g. lysine, arginine etc.
# (3) Function of Proteins
(i) Proteins occur as food reserves as glutelin, globulin casein in milk.
(ii) Proteins are coagulated in solutions, alkaline to the isoelectric pH by positive ions such as etc. Casein – pH 4.6, cyt. C – 9.8, resum globulin 5.4, pepsin 2.7, lysozyme 11.0 etc.
(iii) Proteins are the most diverse molecule on the earth.
(iv) Proteins work as hormone as insulin and glucagon.
(v) Antibiotics as gramicidin, tyrocidin and penicillin are peptides.
(vi) They are structural component of cell.
(vii) They are biological buffers.
(viii) Monellin is the sweetest substance obtained from African berry (2000 time sweeter than sucrose).
(ix) Proteins helps in defence, movement activity of muscles, visual pigments receptor molecules, etc.
(x) Natural silk is a polyamide and artificial silk is a polysaccharide. Nitrogen is the basic constituent.
Protein : The word protein was coined by Berzelius in 1838 and was used by G. J. Mulder first time 1840. 15% of protoplasm is made up of protein. Average proteins contain 16% nitrogen, 50–55% carbon, oxygen 20–24%, hydrogen 7% and sulphur 0.3 – 0.5%. Iron, phosphorous, copper, calcium, and iodine are also present in small quantity.
# (1) Structure of proteins : It is due to different rearrangement of amino acids. When carboxyl group of one amino acid binded with amino group (– NH2) of another amino acid the bond is called peptide bond. A peptide may be dipeptide, tripeptide and polypeptide. The simplest protein is Insulin. According to Sanger (1953) insulin consists 51 amino acids. A protein can have up to four level of conformation.
(i) Primary structure : The primary structure is the covalent connections of a protein. It refers to linear sequence, number and nature of amino acids bonded together with peptide bonds only. e.g. ribonuclease, insulin, haemoglobin, etc.
(ii) Secondary structure : The folding of a linear polypeptide chain into specific coiled structure helix) is called secondary structure and if it is with intermolecular hydrogen bonds the structure is known as pleated sheet. helical structure is found in protein of fur, keratin of hair claws, and feathers. pleated structure is found in silk fibres.
(iii) Tertiary structure : The arrangement and interconnection of proteins into specific loops and bends is called tertiary structure of proteins. It is stabilized by hydrogen bond, ionic bond, hydrophobic bond and disulphide bonds. It is found in myoglobin (globular proteins).
(iv) Quaternary structure : It is shown by protein containing more than one peptide chain. The protein consists of identical units. It is known as homologous quaternary structure e.g. lactic dehydrogenase. If the units are dissimilar, it is called as heterogeneous quaternary structure e.g. hemoglobin which consists of two chains and two chains.
# (2) Classification of proteins : Proteins are classified on the basis of their shape, constitution and function.
On the basis of shape
(i) Fibrous protein/Scleroprotein : Insoluble in water. Animal protein resistant to proteolytic enzyme is spirally coiled thread like structure form fibres. e.g. collagen (in connective tissue), actin and myosin, keratin in hairs, claws, feathers, etc.
(ii) Globular proteins : Soluble in water. Polypeptides coiled about themselves to form oval or spherical molecules e.g. albumin insulin hormones like ACTH, oxytosin, etc.
On the basis of constituents
(i) Simple proteins : The proteins which are made up of amino acids only. e.g. albumins, globulins, prolamins, glutelins, histones, etc.
(ii) Conjugated proteins : These are complex proteins combined with characterstic non–amino acid substance called as prosthetic group. These are of following types :–
(a) Nucleoproteins : Combination of protein and nucleic acids, found in chromosomes and ribosomes. e.g. deoxyribonucleoproteins, ribonucleoproteins, etc.
(b) Mucoproteins : These are combined with large amount (more than 4%) of carbohydrates e.g. mucin.
(c) Glycoproteins : In this, carbohydrate content is less (about 2 – 3%) e.g. immunoglobulins or antibiotics.
(d) Chromoproteins : These are compounds of protein and coloured pigments. e.g. haemoglobin, cytochrome, etc.
(e) Lipoproteins : These are water soluble proteins and contain lipids. e.g. cholesterol and serum lipoproteins.
(f) Metalloprotein : These are metal binding proteins, AB1–globin known as transferring is capable of combining with iron, zinc and copper e.g. chlorophyll.
(g) Phosphoprotein : They composed of protein and phosphate e.g. casein (milk) and vitellin (egg).
# (iii) Derived proteins : When proteins are hydrolysed by acids, alkalies or enzymes, the degredation products obtained from them are called derived proteins. On the basis of progressive cleavage, derived proteins are classified as primary proteoses, secondary proteoses, peptones, polypeptides, amino acids, etc.
On the basis of nature of molecules
(i) Acidic proteins : They exist as anion and include acidic amino acids. e.g. blood groups.
(ii) Basic proteins : They exist as cations and rich in basic amino acids e.g. lysine, arginine etc.
# (3) Function of Proteins
(i) Proteins occur as food reserves as glutelin, globulin casein in milk.
(ii) Proteins are coagulated in solutions, alkaline to the isoelectric pH by positive ions such as etc. Casein – pH 4.6, cyt. C – 9.8, resum globulin 5.4, pepsin 2.7, lysozyme 11.0 etc.
(iii) Proteins are the most diverse molecule on the earth.
(iv) Proteins work as hormone as insulin and glucagon.
(v) Antibiotics as gramicidin, tyrocidin and penicillin are peptides.
(vi) They are structural component of cell.
(vii) They are biological buffers.
(viii) Monellin is the sweetest substance obtained from African berry (2000 time sweeter than sucrose).
(ix) Proteins helps in defence, movement activity of muscles, visual pigments receptor molecules, etc.
(x) Natural silk is a polyamide and artificial silk is a polysaccharide. Nitrogen is the basic constituent.