Nucleic Acids

Nucleic acids are information molecules that are used by all organisms to store hereditary information that determines structural and functional characteristics. They contain information in coiled chains of deoxyribonucleic acid (DNA) and are the only molecules that can create exact copies of themselves and allow organisms to reproduce. All organisms pass to their offspring their unique sequence of nucleotides in their DNA.

Another nucleic acid is RNA, which reads the information in DNA and transports it to the protein-building part of the cell. DNA and RNA are both nucleotide polymers, and the subunits in both molecules contain a nitrogen base, a five-carbon sugar, and a phosphate group. The difference between DNA and RNA is that DNA contains the sugar deoxyribose, whereas RNA contains ribose. The only difference between deoxyribose and ribose is the lack of an oxygen atom in ribose.

There are five types of organic bases in nucleic acids;

1) Adenine (A)

2) Guanine (G)

3) Cytosine (C)

4) Thymine (T) Found in DNA ONLY

5) Uracil (U) Found in RNA ONLY

Adenine always bonds to Thymine (T) with TWO hydrogen bonds, and Cytosine (C) always bonds to Guanine (G) with THREE hydrogen bonds. Cytosine, Thymine, and uracil are single-ringed pyrimidines, and adenine and guanine are larger double ringed purines.

Similarily to RNA molecules, DNA molecules are also helical in structure, BUT they are composed of two DNA strands wound around each other like a circular staircase. The two strands are held together by hydrogen bonds between nitrogenous bases on the strands. Each strand of a DNA molecule has a free phosphate group at one end and a free sugar (deoxyribose) at the other end. The free phosphate end lines up with the free sugar end on the opposite strand because hydrogen bonds form only if one strand is upside down compared with the other strand. Because of this, the two strands are considered to be antiparallel.

When a RNA or DNA molecule is built, enzymes link a series of nucleotides to one another to form a polymer called a strand. Enzymes look over the formation of covalent bonds between the phosphate group of one nucleotide to the hydroxyl group attached to the number 3 carbon of the sugar of the other nucleotide. A phosphodiester bond forms as a result of a condensation reaction between two -OH (hyroxyl) groups. RNA molecules form into a helix, but remain single stranded.