Thursday, April 10, 2008


DNA carries the genetic information of a cell and consists of thousands of genes. Each gene serves as a recipe on how to build a protein molecule. Proteins perform important tasks for the cell functions or serve as building blocks. The flow of information from the genes determines the protein composition and thereby the functions of the cell.

The DNA is situated in the nucleus, organized into chromosomes. Every cell must contain the genetic information and the DNA is therefore duplicated before a cell divides (replication). When proteins are needed, the corresponding genes are transcribed into RNA (transcription). The RNA is first processed so that non-coding parts are removed (processing) and is then transported out of the nucleus (transport). Outside the nucleus, the proteins are built based upon the code in the RNA (translation).


Ribonucleic acid or RNA is a nucleic acid made from a long chain of nucleotide units. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell RNA is usually single stranded, while DNA is usually double stranded. RNA nucleotides contain ribose while DNA contains deoxyribose (a type of ribose that lacks one oxygen atom), and in RNA the nucleotide uracil substitutes for thymine, which is present in DNA.

RNA is transcribed from DNA by enzymes called RNA polymerases and is generally further processed by other enzymes. Some of these RNA-processing enzymes contain RNA as part of their structures. RNA is also central to the translation of some RNAs into proteins. In this process, a type of RNA called messenger RNA carries information from DNA to structures called ribosomes. These ribosomes are made from proteins and ribosomal RNAs, which come together to form a molecular machine that can read messenger RNAs and translate the information they carry into proteins. It has also been known since the 1990s that several types of RNA regulate which genes are active.

A hairpin loop from a pre-mRNA. Notice its nitrogen-rich (blue) bases and oxygen-rich (red) backbone.
A hairpin loop from a pre-mRNA. Notice its nitrogen-rich (blue) bases and oxygen-rich (red) backbone.