Comment Importance of Non-Coding Regions (Score 1) 194
First, on the subject of DNA damage...
The point offered by afidel is relatively accurate. DNA damage happens, for the most part, at a pretty level rate. Damage from oxidative free radicals from metabolic functions... damage from environmental mutagens... etc. It's all pretty much a function of number of lesions per region of DNA that can be induced. Now if those factors are going to remain pretty much even, you stand a better chance of a lesion striking important DNA if that's all you have...
Someone mentioned bacteria have very little junk. Heck, along that line, viruses have the least. In fact, those little bastards jam more genes into a span of DNA that they make everything else look bad (like coding genes on BOTH strands of the double helix, not just one). But, one needs to remember simple organisms actually thrive on high rates of mutation. HIV is particularly virulent because of mutant. Bacteria strains become better suited for harsh environments during parasitic invasion through mutation. Mutation happens through damage. Sure, a bunch die when they get lethal mutations.. but considering the numbers of bacteria or viruses produced, it's worth it if a stronger variant can arise. Hence why bacteria still retain very low fidelity DNA replication. complex organisms on the other hand, evolve slower and can't risk drastic change because of our limited ability for offspring. Keep in mind, in your mouth right now you have more bacteria than people that have ever lived. Since we can't just take pot shots at evolution like bacteria can, we've evolved to be very stringent about the condition of our DNA.
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On to other uses for 'junk' DNA. A lot of it seems to hold structural functions. Even gross deletions of noncoding DNA can be deleterious. Chromosomes fold and bundle, exposing certain regions for expression... this is a function of structural gene segments. One poorly understood section is the X-control region. Originally found in mice, this determines which of the two X chromosomes in females in inactivated. Recently found a similar region in humans and it's still poorly understood but it doesn't appear to code for anything, but it is involved in important epigenetic regulation.
hey.. there's the R word. Regulation. Huge spans of DNA upstream of genes, sometimes even downstream of genes, and often right smack dab in the middle of genes, are important in regulation. Binding sites for transcription factors.. Regions possibly involved in transcription stability.. etc. The bits of DNA that are cut out before translation are even believed to help in stability and transport.
Stuff we just don't know yet. Yep, that's a vague answer... but almost ANYTHING someone can sit there and dream up, evolution has already come up with. Half the time that person dreaming stuff up will be considered a crackpot.. but given enough time, money and resources, chances are you'll find the crackpot is right. That was the case with prions (replicative proteins that never go through a nucleotide intermediate... cause mad cow disease). Or catalytic RNA. Etc etc.. there's so many possibilities, it's really impossible to discount *anything*.
So, that's what I have to offer. Geneticist, signing out.
Ciao, C.Sc.
The point offered by afidel is relatively accurate. DNA damage happens, for the most part, at a pretty level rate. Damage from oxidative free radicals from metabolic functions... damage from environmental mutagens... etc. It's all pretty much a function of number of lesions per region of DNA that can be induced. Now if those factors are going to remain pretty much even, you stand a better chance of a lesion striking important DNA if that's all you have...
Someone mentioned bacteria have very little junk. Heck, along that line, viruses have the least. In fact, those little bastards jam more genes into a span of DNA that they make everything else look bad (like coding genes on BOTH strands of the double helix, not just one). But, one needs to remember simple organisms actually thrive on high rates of mutation. HIV is particularly virulent because of mutant. Bacteria strains become better suited for harsh environments during parasitic invasion through mutation. Mutation happens through damage. Sure, a bunch die when they get lethal mutations.. but considering the numbers of bacteria or viruses produced, it's worth it if a stronger variant can arise. Hence why bacteria still retain very low fidelity DNA replication. complex organisms on the other hand, evolve slower and can't risk drastic change because of our limited ability for offspring. Keep in mind, in your mouth right now you have more bacteria than people that have ever lived. Since we can't just take pot shots at evolution like bacteria can, we've evolved to be very stringent about the condition of our DNA.
--
On to other uses for 'junk' DNA. A lot of it seems to hold structural functions. Even gross deletions of noncoding DNA can be deleterious. Chromosomes fold and bundle, exposing certain regions for expression... this is a function of structural gene segments. One poorly understood section is the X-control region. Originally found in mice, this determines which of the two X chromosomes in females in inactivated. Recently found a similar region in humans and it's still poorly understood but it doesn't appear to code for anything, but it is involved in important epigenetic regulation.
hey.. there's the R word. Regulation. Huge spans of DNA upstream of genes, sometimes even downstream of genes, and often right smack dab in the middle of genes, are important in regulation. Binding sites for transcription factors.. Regions possibly involved in transcription stability.. etc. The bits of DNA that are cut out before translation are even believed to help in stability and transport.
Stuff we just don't know yet. Yep, that's a vague answer... but almost ANYTHING someone can sit there and dream up, evolution has already come up with. Half the time that person dreaming stuff up will be considered a crackpot.. but given enough time, money and resources, chances are you'll find the crackpot is right. That was the case with prions (replicative proteins that never go through a nucleotide intermediate... cause mad cow disease). Or catalytic RNA. Etc etc.. there's so many possibilities, it's really impossible to discount *anything*.
So, that's what I have to offer. Geneticist, signing out.
Ciao, C.Sc.
