Structural Biochemistry/Nucleic Acid

Nucleosides consist of a base linked to a ribose or deoxyribose sugar. A nucleoside can form a glycosidic bond linking to 1+ phophate group. A nucleoside + one phosphate makes a nucleotide.

Nucleic acid is an important macromolecule because it carries the information in a form that can be passed from one generation to the next. These macromolecules consist of a large number of linked nucleotides which makes off a sugar, a phosphate, and a nitrogenous base (either a purine or pyrimidine). Purines- Adenine and Guanine. Pyrimidines- Cytosine, Uracil, and Thymine. Sugars and phosphates are linked through the esterphosphate bond created the common backbone that plays a structural role. On the other hand, the sequence of bases along a nucleic acid chain carries the genetic information.

Two of the most common nucleic acids known are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Between the two, they differ by only a hydroxyl group and the bonding between the nucleic acids by which will be discussed further in the deoxyribonucleic and ribonucleic section of the wikibook.



History
In 1870, Johann Friedrich Miescher was the first person that isolated the components of DNA. He found a weakly acidic substance of unknown function in the nuclei of human white blood cells and named it "nuclein". In the 1920s, it was discovered that nucleic acids was a major components of chromosomes. Elemental analysis showed the presence of phosphorous, 2-deoxyribose sugar, and four different heterocyclic bases. The two monocyclic bases are classified as pyrimidines, and the other two bicyclic bases are purines.

Until the late 1940s and early 1950s, DNA was determined to play a main role in inheritance. The structure of DNA more than ever become a universal interest in scientific world. Erwin Chargaff was a pioneer that tried to construct the composition of DNA. He found that the amount of adenine (A) always equaled the amount of thymine (T), and the amount of guanine (G) always equaled the amount of cytosine (C).

Structure of Nucleic Acid
A nucleic acid contains three parts: a phosphate group, a sugar group (deoxyribose or ribose), and a base. The bases are adenine, guanine, cytosine, and thymine (uracil for RNA). When a base is attached to a sugar group it is called a nucleoside. The four nucleosides for DNA are deoxyadenosine, deoxyguanosine, deoxycytidine, and thymidine. The four nucleosides for RNA are adenosine, guanosine, cytidine, and uridine. A nucleotide is when a nucleoside is bound to one or more phosphate groups. The four nucleotide units of DNA are called deoxyadenylate, deoxyguanylate, deoxycytidylate, and thymidylate.

Nucleotides have a distinctive structure composed of three components that held together by covalent bond:a nitrogen-containing base (cytosine, thymine, aconine, guanine, a 5-carbon sugar – ribose or deoxyribose, a phosphate group.



The polymer of nucleotide is nucleic acid. It is built by forming phosphodiester bonds between the 3' carbon of one nucleotide and the 5' carbon of another nucleotide, creating sugar-phosphate backbone.