Biology PROTEINS

Proteins

Protein name is derived from a greek word which means " holding first place" (Berzelius and Mulder)
`->` Essential elements in protein are `C , H , O, N`,

`->` Most of the proteins contain sulphur. In some proteins iodine , iron and phosphorus are present.

`->` After water, proteins are most abundant compounds in protoplasm. (`7-14%`) amount of proteins.

`->` Proteins are polymer of amino acid (Fisher and Hofmeister). There arc approximately `300` amino acids known to exist but only `20` types of amino acids are used in formation of proteins

`->` Proteins are hetero Polymer of amino acid.

`->` Amino acids contain an amino group and carboxylic group on the same carbon i.e. the `alpha.-carbon` so they are called `alpha`-amino acid.

`->` Amino acid are substituted methane.

Each amino acid is amphoteric compound because it contains one acidic `-COOH` and a alkaline group `-NH_2`

`->` In protoplasm free amino acid occurs as ions (at iso electric point)

`->` Iso electric point is that point of pi I at which amino acids do not move in electric field.

`->` Out of `20` amino acids, `10` amino acids are not synthesi;ced in body of animals so they are must in diet. These
are called Essential amino acid . e. g. Threonine . Valine, Leucine, Isoleucine. Lysine, Methionine, phe-
nylalanine Tryptophan, Arginine. Histidine. Arginine and Histidine are semi essential.

`->` `10` amino acids are synthesized in animal body so these are called Non essential amino adds. for e.g.
Glycine, Alanine, Serine. Cysteinc,Aspartic acid, Clutamic acid, Asparaginc, Clutamine, Tyrosine, proline

Except glycine, each amino acid has two enantiomeric isomers

`->` Eucaryotic proteins have L- amino acid while D- amino acid occurs in bac1cria and antibodies.

Classification of amino acids

Classification of amino acids on the basis of number of carboxylic groups and Amino groups.

1. Acidic amino acid
`->` They have one amino and two carboxylic groups in their structure.

Net charge = -ve, so they move towards anode in electric field.
e.g. -Glutamic acid

2. Alkaline amino acid

`-> ` They have two amino and one carboxylic group.

Net charge +ve, so they move towards cathode in electric field.

e.g. Histidine
Arginine
Lysine

3. Neutral AA

`-> ` They have one amino and one carboxylic group.

`->` They are present in the form of zwitter ion and show no movement in electric field.
e.g. Rest 15 AA

Special Points on Amino acid :

1. Tryptophan : Most complex amino acid and helpful in synthesis of I.A. A. (lndole-3-Acetic Acid) which is plant growth hormone.

2. Tyrosine : Helps in synthesis of melanin pigment, Thyroxine hormone, Adrenaline (epinephrine) hormone, Nor adrenaline (Nor epinephrine) Hormone.

3. In proline and hydroxy proline amino acids, imino group `(-underset(|)NH)` is present instead of amino `(-NH_2)` group
so these two amino acids are also known as imino acid.

4. Cysteine and methionine are sulphur containing amino acid.

5. `tt ( (text(Tyrosine)) , (text(Tryptophan)) , (text(Phenl alanine)) ) }` `tt( (text(Aromatic AA)) , (text(because they have)) , (text(benzene ring in their structure)) )`

6. `tt ( (text(Proline)) , (text(Hydroxyproline)) , (text(Histidine)) ) }` `tt( (text(Heterocyclic AA)) , (text(because they have)) , (text(heterocyclic )) )`

7. `tt ( (text(Serine)) , (text(Threonine)) ) }` `tt( (text(Alcoholic AA)) , (text(because they have -OH)) , (text(group in their structure)) )`

8. Except glycine all amino acids are laevorotatory.

9. Glycine is the simplest and Tryptophan is complex Amino acid.

10. Amino acids which participate in protein synthesis called protein Amino acid and which do not participatecalled non-protein.
eg. GABA, Ornithine, Citrulline.