One-gene-one-enzyme hypothesis
The one-gene-one-enzyme hypothesis is the hypothesis that a gene carries the information for the formation of a certain enzyme , i.e. a catalytically active protein molecule .
Back in 1909 the British doctor had Archibald Garrod inborn errors of metabolism (English inborn errors of metabolism ) are identified and suggested that as in the case of Alkaptonurie vorliege an enzyme defect, which is genetically fixed. The hypothesis of a gene - an enzyme was developed in the 1940s by George Beadle and Edward Tatum and substantiated experimentally on the mold Neurospora . For this work they received the Nobel Prize in Physiology or Medicine in 1958 . This hypothesis is now only valid to a limited extent.
In general, a segment of DNA can code for a protein . This can, but does not have to , have a catalytic effect. Also structural proteins are encoded directly in the DNA, and are represented by the protein biosynthesis formed. In the course of the elucidation of this synthesis, the hypothesis had to be modified. Since, on the one hand, many enzymes consist of several polypeptide chains and, on the other hand, structural proteins without a catalytic effect, such as keratin in hair, are produced in the same way, the hypothesis of the one-gene-one polypeptide hypothesis was modified.
In eukaryotes , the same DNA segment often leads to different mRNA molecules and thus different proteins. The cause is the alternative splicing , through which it is first decided which DNA segments of a gene encode, i.e. are exons , and which are cut out during the maturation process ( introns ).
With the discovery of alternative splicing in the transcription of eukaryotes , the hypothesis had to be modified again. Different processing (splicing) of the pre-mRNA generated on the DNA can result in several different mature mRNA molecules and thus several different polypeptides from the same DNA sequence. The regulation has not yet been fully clarified.
Further limitations of the hypothesis
RNA molecules synthesized on the DNA can bind to other mRNA molecules and form double strands. These are then destroyed by the cell. This RNA silencing allows an RNA sequence to act as a subsequent gene switch and influence other genes.
RNA molecules can also act as biocatalysts on their own or in combination with proteins , i.e. they function like enzymes ( ribozymes ). The active center can be formed exclusively by RNA.
The rRNA is also transcribed by genes, but not translated into a polypeptide chain.
According to the current state of research, the hypothesis can be modified as follows:
- A gene encodes a biologically active RNA. This is not necessarily translated into a polypeptide.
swell
- ↑ George W. Beadle, Edward L. Tatum: Genetic Control of Biochemical Reactions in Neurospora. In: Proceedings of the National Academy of Sciences of the United States of America . Vol. 27, No. 11, 1941, pp. 499-506, PMID 16588492 , PMC 1078370 (free full text).
- ↑ George W. Beadle: Biochemical Genetics. In Chemical Reviews . Vol. 37, No. 1, 1945, pp. 15-96, doi : 10.1021 / cr60116a002 .
- ↑ Information from the Nobel Foundation on the 1958 award ceremony for George Beadle and Edward Tatum (English)