DNA or deoxyribonucleic acid is an essential constituent of all living organisms and contains the genetic information necessary for the propagation of life. Every cell contains DNA molecules. In the case of eukaryotic cells, such as plant and animal cells, DNA molecules reside in the cell nucleus. In the case of prokaryotic cells, such as bacteria, the DNA molecule is in the cytoplasm of the cell (since there is no membrane-bound nucleus). The DNA molecule itself is composed of two complementary strands connected together (by hydrogen bonding) to produce a double helical structure. DNA contains the information necessary for the synthesis of proteins in the cell and thus contains information required for the functioning of the cell. This genetic information is passed from the parent cell to the daughter cells during cell division, with each DNA strand acting as the template for its complementary strand. 

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What is the function of DNA?

DNA is a double stranded helical structure. It is a polynucleotide made up of nitrogenous base pairs like adenine, guanine, cytosine, thymine, phosphate group, and deoxyribose sugar.

The structure is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate and the bases project inside. The two chains have anti-parallel polarity. It means, if one chain has the polarity 5'?3', the other has 3'?5'.

The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds.

As for function, DNA helps in storing genetic information in form of genes. It stores biological information in a coded form, transfers it to the next generation, and causes its expression in the offspring.

As for the prokaryotic cell-DNA is circular and occurs in the cytoplasm. In the eukaryotic cell, DNA is linear and confined to the nucleus (nuclear DNA). A small quantity of circular DNA also occurs in the mitochondria and in chloroplasts (plants) as in extranuclear or organellar DNA and extrachromosomal DNA.