Deoxyribonucleic acid is one of the major biomolecules that altogether form living organisms. DNA is a long, chainlike molecule comprising several repeating chemical units. Each of these repeating units is composed of a sugar molecule, a nitrogenous base and a phosphate group. DNA is often called the molecule of life as it provides the instructions that make any living organism function properly.
DNA as a Chemical
A chemical analysis of DNA reveals its nucleotide building blocks, the components of the nucleotides and the different elements that make up these components. The sugar part of DNA consists mostly of carbon, oxygen and hydrogen, while the phosphate group is composed of phosphorus and oxygen. The nitrogenous base is more complex and contains carbon, hydrogen, oxygen and nitrogen.
The Backbone of DNA
DNA is formed by connecting the nucleotides using chemical bonds between the ringlike deoxyribose sugar and the phosphate. Such bonds are called phosphodiester bonds, and the resulting chain of alternating sugar and phosphate is called the sugar-phosphate backbone. The nitrogenous base is not part of the backbone and instead sticks out of it.
Providing DNA Variation
One of the hallmarks of DNA is that it's different from one organism to another. This difference is due to the variation in the sequence of the nitrogenous bases in the nucleotides. Nitrogenous bases are flat, ring-shaped molecules. There are four kinds of nitrogenous bases used in DNA: adenine, cytosine, thymine and guanine. The first letters of the nitrogenous bases, namely A, C, T and G, are used as their symbols. Unexpected and unnecessary changes in the sequence of bases are called mutations and can lead to diseases such as cancer.
Double Helical Form
DNA has a double helix structure composed of two partner DNA strands and cannot exist as a single DNA strand. The double-strand structure is due to the formation of hydrogen bonds between the nitrogenous bases of the partner DNA strands. DNA can "melt," meaning that it separates into single strands when exposed to the appropriate enzyme or when incubated at high temperatures. DNA is soluble in water but is insoluble in other solvents such as ethanol. This property can be used to extract it from cells.
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