Biology: What are DNA and its components?

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What are DNA?

Eukaryotic chromosomes consist of protein and deoxyribonucleic acid (DNA), in about equal amounts. DNA is the hereditary material that makes up chromosomes and genes. DNA was first isolated by Friedrich Miescher, a German physician, in 1869. The substance that he isolated was white, sugary, slightly acidic, and contained phosphorus. Since he found that substance in the nuclei, he called it "nuclein." 

Later on, Robert Feulgen, discovered that DNA was present in all cells and was located in the chromosomes. However, it was not until 1950s that scientists were able to understand some of the main functions of DNA when the Watson-Crick model came out. 

Watson-Crick model stated that DNA is an exceedingly long, entwined double helix. 

DNA contains four nitrogenous bases: 

adenine (A) 

thymine (T)

guanine (G)

cytosine (C) 

These nitrogenous bases make up each of the double-strands of DNA. The bases of the two strands are connected to each other via hydrogen bonds.  Each base is also covalantly bonded to a sugar-phosphate base.  Nucleotides along each strands could be assembled in any order: for example, TTCGGGATCCATATG. 

Watson-Crick model also explained how more strands of DNA could be produced in a process called replication.  A new DNA strand is always synthesized in one particular direction. The strand that is continuously synthesized is called the leading strand, while the lagging strand gets synthesized discontinuously in short pieces running opposite to the direction of replication fork movement. 

DNA consists of 5 elements:  

nitrogen

carbon

hydrogen

oxygen

phosphorous 

The best way to illustrate this essential organic molecule is to view DNA as a rope that has two strands. These strands have locked and wrapped each other in a way that if you twist the rope in one way, it becomes more concentrated, and if you twist it in the other direction, it becomes less dense and less concentrated.  

DNA molecules are very long, but have you ever wondered how these long molecules are being fit in a tiny cell?  

The answer is simple and yet profound.  The DNA molecule twists itself with the help of different enzymes in order to become denser and more concentrated.  When a DNA wants to go through a replication process; however, it must go back to its untwisted form.  This process once again requires different enzymes.

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