Many of these genes lack homology to characterized genes and are of unknown function.
Many genes that appear to have origins outside the enteric bacteria, as deduced from their different base composition, were found on the smaller chromosome. Together, this totals approximately 4 million base pairs and encodes about 3900 proteins-about the same amount of genetic information as E. Having an RNA intermediate allows the information in DNA to travel from the nucleus to the cytoplasm.When the genome of the Gram-negative bacterium Vibrio cholerae, the causative agent of cholera, was sequenced, it was found to consist of two circular chromosomes of 2,961,146 and 1,072,314 bp. In addition, in eukaryotes DNA is kept in the nucleus, while translation happens on ribosomes (found in the cytoplasm). This allows cells to be much more responsive to changing conditions. There are also multiple levels of regulation that can control how much mRNA is present, what parts of the mRNA get kept‡, and how frequently the mRNAs get translated. This is because many mRNAs can be transcribed from a gene and then each mRNA can be translated independently (and multiple times). Making mRNA also allows efficient production of proteins from a single gene.
(You'd have to redesign life from scratch!) This means that we use RNA because "life" has always used RNA and getting rid of it by evolutionary processes would be essentially impossible. One strongly supported hypothesis is that RNA actually came first - this known as the "RNA world hypothesis"§.
This is an interesting question to think about, but "why" questions in biology are often very difficult to answer in a meaningful way.īelow I've listed one possible evolutionary reason for the use of mRNA as an intermediary and then some advantages to this system.
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