Genetic Code

The genetic code is a set of all codones. Codone is a code formed by three nucleotides. Nucleotides in human DNA are adenin (A), guanin (G), thymin (T) and cytosin (C). In RNA one of them - thymin - is replaced by uracil (U).

According to the order of codones the expresion takes place. Aminoacids (coded by codones) are the main building components of all the proteins.

The genetic code has 4 main features, which are typical for it:

The genetic code is degenerate
We know just 21 aminoacids, but they can create 61 different combinations - codones. It logically means that one aminoacid is coded by more than one codone. The codone is created by 3 nucleotides. We can say, that the nucleotide on the last possition is the less important. Some aminoacids are coded just by one codone (methionin, tryptofan). On the other hand serin has 6 possible combinations.

The genetic code is non-overlapping
During proteosyntesis the genetic code is read in special order - one by one. The is no possibility to overlapping some of the nucleotide. The process starts from an iniciative codone and then continues until it reaches termination codone.

The genetic code is universal
The genetic code is pretty similar in most of the organisms. This point is not exactly true, how the scientists discovered. Newly, we know that there are many exceptions from this rule. In past it was said that genetic code in human is similar to genetic code of some lower organisms. It means that codone, which codes methionin in human, do the same in prokaryotes too. Nowadays, we know that it should not be the truth. The genetic code is not universal, but it is still predominant.

The genetic code is uniform
This feature related to the first point. One aminoacid can be coded by more codones. But one codone can codes just ONE aminoacid,no more. It is a big difference. Then it is called "uniform".



Related articles

 * Codone
 * Proteosyntesis
 * Translation
 * Expresion