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DNA deterioration

  1. Nov 11, 2007 #1
    I read that a lot of aging is caused by DNA and mtDNA getting damaged, I was wondering if anyone knew of how much it gets damaged, like say if someone is X years old then the average cell's DNA is Y% correct of what it was originally. Or are changes to DNA much more rare, and if a small change happens does it turn into a cancerous cell or do small changes happen often with no apparent consequences. Same questions for mtDNA.

    If someone wanted to preserve both types of DNA with no deterioration, what would be the way to do it? I see a lot of companies that preserve DNA for parental testing and stuff, but I am not sure if they preserve it perfectly or just good enough to do their testing.
  2. jcsd
  3. Nov 12, 2007 #2

    jim mcnamara

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    This actually is a branch of genetics with its own name - epigenetics.
    Your body switches DNA off/on by causing histones to bind with DNA sections - sort of how cell differentiation is thought to occur - ie., a cell "decides" to become a liver cell.
    Sometimes the switching on/off goes wrong and creates DNA that cuases the cell to die or to grow irregularly. So, in this sense, we kind of do ourselves in.

    Real problems start to arise when environmental factors cause other kinds of DNA changes - example methylation of DNA. In this case it is not our body changing DNA it is the environment. This happens to every living thing, all the time.

    Whether it is bad for the organism or not is determined by other unaffected genes and possibly other environmental effects on DNA. People who live completely away from modern industrial chemical exposure in food, air, etc. have the least damage. But, the tradeoff is that folks living on "manual labor" farms or as nomadic shepherds, in remote areas, are far more likely to die early from things like infectious disease or crop failure or a devastating weather problem.
  4. Nov 12, 2007 #3
    The majority of small changes I believe you are referring to (SNPs or Single Nucleotide Polymorphisms) will have little to no effect depending on where it happens. For example, if it happens on the 1st base of a codon then it will most likely change that amino acid, but the 3rd base would probably have little effect. Also genes that are commonly expressed also become conserved and unergo less polymorphisms. Most SNPs occur in introns and regions that lie in between gene coding regions.

    As far as aging goes, the build up a free radicals can be detrimental along with other factors, such as Jim pointed out.

    In reference to preservation of DNA in the lab, generally this is done by freezing the sample at around -80C for storage.
  5. Nov 14, 2007 #4
    My main question is if you took say 10,000 cells from a 85 year old person, how close would the DNA be to the the DNA of that person when they were born, and the same question for for mtDNA, which I understand would get damaged faster.
    Last edited: Nov 14, 2007
  6. Nov 14, 2007 #5

    jim mcnamara

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    There have been monozygotic twin studies looking at differences in methlyation of DNA in older individuals. The assumption was that because the twins started out with identical DNA, methylations and all, any differences found between the twins was a reflection of the changes to DNA over the individual's lifetime. The differences in younger twins was minimal. In older twins differences were very obvious. See the third page of this press release article for some graphics:

  7. Nov 15, 2007 #6
    I was talking about oxidative damage, not epigenetic changes.
  8. Nov 15, 2007 #7

    jim mcnamara

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    Define oxidative damage, please. Free radicals damaging DNA? DNA does have repair mechanisms to prevent that kind of damage from being replicated into other cells.
    Cell death also stops propagation. This type of damage is more localized to particular tissues and most particularly to non-dividing cells. It is also one of the hypotheses for the aging process.

    I do not know of studies relating DNA oxidative stress levels, subsequent damage and time. Sorry.
  9. Nov 16, 2007 #8
    Yes free radicals damaging DNA.

    So are you saying oxidation does not cause problems? If that is so then how come it is seen as one of the main causes of aging?

    This is what I would like to know: when you see someone who is say 100 years old, they look a lot different than they looked when they were 25, their skin looks different, their hair looks different, it tends to be more irregular like they have different colored patches of skin, my question is are those differences caused by DNA damage?
  10. Nov 16, 2007 #9

    jim mcnamara

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    I got the part about free radicals, thanks. I thought I answered that part of the question - I guess not. DNA is damaged by oxidation. Period.

    Your hidden assumption: oxidative damage is the only important part of DNA change during a lifetime.

    My answer: no. It is not.

    So, before you decide to read on, are we on the same page?

    Your Question
    My answer:
    In part, yes.
    The "epigenetics" you don't want to consider is the other part.

    [science fact]
    Anything that changes DNA behavior can result in changes to: the way you look; organ function, etc. It also affects cell differentiation - whether cells "decide" to replace themselves or not, or whether to regrow damaged tissue or not. If it speeds up when cells decide to divide, it can cause neoplasms - tumors, cancer[/fact]
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