Domains of Life; Prokaryotic vs. Eukaryotic Cells

ID #2325

In lecture you discussed the "word" that tells us how close we are to another organism. I understand that, but does it matter what letter in the word is altered? Does the 7th letter being different make it closer than if the 1588th letter was different?

Sometimes, the specific position of a given "letter" is important in determining how closely related two different "words" are, e.g. a T at position 7 may be very important. The more differences between two different "words," the more distantly related they are. For example, if you compare the words "fort" and "port," there is only one difference at the first position. The words "fort" and "frog" have three differences, however, so "fort" and "port" are more closely related than "fort" and "frog." Archaea rRNA sequences have more similarities with eukaryotic rRNA sequences, so archaea and eukaryotes are more closely related. 
In the context of rRNA specifically, which is the molecule that was used by Carl Woese in the discovery of Achaea, Prof Mehrtens mentioned that rRNA is highly conserved so that any change is significant in the determination of relatedness between two organisms. Another aspect to consider is if regions within the rRNA or “word” are prone to differences in the spelling. In that case, the location of the different letter does matter. For example, take the spelling of the word “liter”. If you switch the last two letters, as is common in this word, to “litre,” you have the same word with the same meaning, just with a British spelling. If you switch the first letter creating “biter” you have a major change. This is an example of one change being more significant than another in a word and in a way that is similar to changes in spelling of rRNA. 
In this context, the determination of the importance of change in spelling of a word is quite complicated and now people use software to aid in this. In this class, you will not be expected to rank importance of changes of spelling of the rRNA “word.” 

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