On Wed, 12 Feb 2003 14:33:28 +0000 (UTC),
lamoran{at}bioinfo.med.utoronto.ca (Laurence A. Moran) wrote:

>In article ,
>William Morse   wrote:
>>wlhunt{at}earthlink.net (William L Hunt) wrote in
>>news:b2103a$1lfc$1{at}darwin.ediacara.org: 
>
>[snip]
>
>>>  Genome size range for Bacteria are about 580 - 13,200 Kb (certain
>>> Cyanobacteria at 13,200Kb)
>>>  Archaea about 1,600 - 4,100 Kb
>>>  Variation is almost all due to number of genes since there is little
>>> non-coding DNA. 
>>>  Eukaryotes range from 8,800 Kb - 686,000,000 Kb. So some bacteria
>>> have genomes larger than the smaller eukaryotic genomes. Baker's yeast
>>> has a genome of 12,000 Kb but (given sufficient nutrient) it may be
>>> able to replicate faster than a bacteria of same genome size. Bacteria
>>> replicate from a single replication point on their circular DNA but
>>> eukaryotes use multiple initial replication points. This puts a severe
>>> constraint on the genome size of bacteria.
>>>  William L Hunt 
>
>>Thank you. So the effiency of the lack of junk may be due to difficulty 
>>in rapid replication rather than the energy cost of reproducing non-
>>coding DNA. 
>
>Bacterial genomes do contain junk DNA. They just don't have as much of
>it as some eukaryotes. The reason is probably because of selection for
>small size and reasonable energy efficiency. The rate of DNA replication
>in bacteria probably doesn't play much of a role since DNA is usually 
>completely copied in only about 5% of the time it takes for a typical
>generation in the real world.
>
>>I would note that the yeast genome is still small by 
>>eukaryote standards (how much is non-coding?) 
>
>About 75% of the yeast genome consist of genes. This includes those
>genes that encode functional RNA's and it includes introns in protein-
>encoding genes. Introns make up 4% of the genome. Of the remaining 
>intergenic DNA, about 5% is known to be junk such as pseudogenes and 
>degenerate transposons. 
>
>>And bacteria have been 
>>around for a long time. If multiple replication points were important why 
>>weren't they developed? 
>
>Many species of bacteria have multiple chromosomes and each one has its
>own replication origin. This is especially true of bacteria with larger
>genomes.
>
>>Perhaps because once eukaryotes evolved their 
>>other advantages allowed them to outcompete large genome bacteria. 
>
>Bacteria are among the most successful species on this planet. 
>In general, eukaryotes do not compete successfully with bacteria.
>Instead, they go for other niches that are't open to bacteria. They
>also provide nice warm homes for many species of bacteria. 
>
>
>
>Larry Moran
>
Very true with one samll nit -- eukaryotes do provide very nice homes
for many species of bacteria but very few of those homes are warm!
Only a very tiny number of species keep ourselves warm, although 
the ones that do include one particular weird example of some
econonic importance.
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