The chemical components of chromosomes are nucleic acids, proteins and other components.
1. Nucleic acid: Chromosome contains 45% nucleic acid. There are two types of nucleic acids. DNA and RNA.
(i) DNA: Deoxyribonucleic acid is abbreviated as DNA. The smallest part of the chromosome that is self-reproducing, regulates biological functions and transmits heritable characteristics and is capable of causing variation, mutation and evolution of organisms is called DNA. It is composed of three chemical substances. Nitrogen bases, pentose sugars and phosphoric acid. Nitrogenous alkalis are of two types. Purines and pyrimidines. Purines are adenine and guanine and pyrimidines are thymine and cytosine. According to scientists Swift (1964) and Bonner (1968), the ratio of DNA and histone proteins in chromosomes is 50:50 or 1:1. About 90% of an organism’s DNA is contained in chromosomes.
(ii) RNA : Ribonucleic acid is abbreviated as RNA. The monomeric units of nucleotides of nucleic acid are made up of ribose sugar, adenine, guanine, cytosine, uracil and phosphoric acid is called RNA. It is composed of three chemical substances. Nitrogenous bases, pentose sugars and phosphoric acid. Nitrogenous alkalis are of two types. Purines and pyrimidines. Purines are adenine and guanine and pyrimidines are cytosine and uracil.
2. Proteins: Proteins form the basic structure of chromosomes. Chromosomes contain 55% protein. Chromosomes contain two types of proteins. Histone proteins and non-histone proteins.
(i) Histone proteins: The major proteins of chromosomes are histone proteins. Histone proteins are alkaline because they contain more lysine and arginine. It forms nucleosome. There are five types of histone proteins. These are-
* Histone-1 (H1): Its molecular weight is 23,000 daltons. It is very high in lysine.
* Histone-2A (H2A): Its molecular weight is 14,000 daltons. It contains slightly more lysine than arginine.
* Histone-2B (H2B): Its molecular weight is 13,800 daltons. It contains a little more lysine.
* Histone-3 (H3): Its molecular weight is 15,300 daltons. It is high in arginine.
* Histone-4 (H4): Its molecular weight is 11,300 daltons. It is high in arginine. Lysine content is slightly higher.
(ii) Non-histone proteins: All proteins other than the histone proteins of chromosomes are called non-histone proteins. The protein structure that remains on the chromosome after the removal of histone proteins is called the scaffold. Non-histone proteins are acidic in nature when tyrosine and tryptophan are added.
3. Other components: Chromosomes contain small amounts of lipids, DNA polymerase enzyme, RNA polymerase enzyme, nucleoside trifatase, calcium ion, magnesium ion, iron ion etc.