General and physical characteristic of proteins

(a) Most of them apart from chromoproteins are colourless, tasteless, and odourless. Several are amorphous but few are crystalline. They are nonvolatile and do not comprise a sharp melting point.

(b) The majority of them are insoluble in water and alcohol. But several of them dissolve in salt solutions, dilute acids and alkalies. Few proteins like keratins (skin, hair and nails) are totally insoluble.

(c) Protein molecules are extremely complex and possess extremely high molecular masses. They are hydrophilic colloids that can't pass through vegetable or animal membrane. Additionally of sodium chloride, ammonium sulphate magnesium sulphate, and so on some proteins are precipitated. The precipitate can be filtered & redissolved in water.