Nucleic acids are large biomolecules, and include both DNA and RNA. DNA, or deoxyribonucleic acid, is genetic material. RNA, or ribonucleic acid, helps the cells make proteins from DNA. Both types of nucleic acids consist of building blocks called nucleotides, though there are subtle differences in the nucleotides that make up the two types of nucleic acids.
Nucleic Acid Structure
While DNA and RNA have much in common, structurally speaking, there are some important differences. Both molecules have chemical "backbones" made up of alternating sugar and phosphate molecules; a phosphate is a compound with the formula PO4. The sugar in DNA is called deoxyribose, while the sugar in RNA is called ribose. Ribose has an extra oxygen molecule compared to deoxyribose. Attached to the backbone are nitrogen-containing bases. RNA consists of a single backbone with bases attached, while DNA looks more like a ladder of two parallel backbones, with bases forming the "rungs," explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Nucleotides
The building block unit of a nucleic acid is called a nucleotide. A nucleotide consists of a single sugar, a phosphate, and a nitrogen-containing base. The nucleotides are all identical within DNA and RNA, with the exception of the bases, which vary and determine the identity of the nucleotide. There are four different bases in DNA, and four different bases in RNA. Both DNA and RNA contain the bases adenine, guanine, and cytosine. RNA uses the base uracil, while DNA uses thymine instead.
Elements
Because of the major similarities between DNA and RNA, they're made of the same elements. The sugars and nitrogen-containing bases contain predominantly carbon and hydrogen. There are also oxygen atoms in the sugars. The phosphates, part of the backbone of both DNA and RNA, consist of phosphorus and oxygen. The nitrogen-containing bases, in addition to carbon and hydrogen, contain oxygen and nitrogen.
Reasons for Differences
The major reason for the differences in structure between RNA and DNA have to do with molecular stability. Deoxyribose makes DNA much more stable than RNA, which is important, because DNA encodes an organism's genetic information for the life of the organism. RNA is a transient molecule that each cell makes and degrades on a regular basis. The single-stranded nature of RNA allows it to perform its function, which is to transmit information quickly, while the double-stranded nature of DNA -- with its two backbones -- allows cells to copy genetic information efficiently.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
