Biochemistry/DNA and RNA

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the information storage molecules and working templates for the construction of proteins. Every living cell and viruse encodes its genetic information using either DNA or RNA. It is a true marvel of evolution that the vast amount of information needed to produce a human being can fit inside cells.

Friedrich Miescher first isolated DNA and RNA from used surgical bandages in 1869. A series of experiments done by Oswald Avery, Colin MacLeod, and Maclyn McCarty in 1944 along with A.D. Hershey and Martha Chase's work in 1952 showed that DNA is the carrier of genetic information. The structure of DNA was discovered by James Watson and Francis Crick in 1953.

Structure of DNA and RNA

DNA is a polymer of nucleotides. Nucleotides consist of a pentose sugar (2-deoxyribose for DNA and ribose for RNA), a phosphate group ($H_{3}P{O}_4$), and a nitrogen-containing base. There are five nitrogen bases - adenine, guanine, thymine, cytosine and uracil. Individual nucleotides are connected by phosphodiester bonds to form polynucleotides.

DNA

DNA exists as a double helix of two (2) strands of polynucleotides. According to the principle of complementarity nucleotides A (adenine) bases are bound with a hydrogen bridge to the T (thymine) or U (uracil in case of RNA) on the other thread and similarly C (cytosine) bind themselves to G (guanine). This principle allows for DNA and RNA replication and for limited possibilities of repairing the genetic information when one of the threads gets damaged.

Difference between DNA and RNA

DNA is the permanent genetic information storage medium, found in the nucleus of most cells of most living organisms. RNA is, in the case of eucaryotes, the medium that transfers the genetic information from the nucleus to the cytoplasm where proteins are synthesized.

There are three major types of RNA:

• messenger RNA (mRNA) - temporarily created RNA used for transferring the information from the DNA to the ribosome where it is "read," or translated, and a protein is synthesized.

• transfer RNA (tRNA) - it is associated with the ribosome and delivers an amino acid to be attached to the growing protein.

• ribosomal RNA (rRNA) - a major constituent of the ribosome with both structural and catalytic properties.

Additionally, by 2005, other types of RNA, such as siRNA (small, interfering RNA) and miRNA have been characterized.