有希大好! asked in 科學生物學 · 1 decade ago

關於遺傳學的現象

可以解釋一下這三個名詞嗎?

基因組烙印(genomic imprinting)

組蛋白乙醯化(histone acetylation)

DNA甲基化(DNA methylation)

可以比較這三樣東西有何相同與相異處嗎?

謝謝!!

Update:

用英文OK!!

1 Answer

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  • C C
    Lv 6
    1 decade ago
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    would you mind an answer in english?

    2009-02-08 03:12:19 補充:

    Ok, it is important to define some terms first:

    Histone Acetylation is when histones (which are protein structures that DNA wrap around) is acetylated by an enzyme. The acetylation neutralizes the postive charges usually associated with the histone protein. Because DNA is negatively charged, this reduction in positive charge cause the histone and the DNA to be less associated. As a result, the DNA is a little bit more 'opened up' for access by transcription factor, and hence it is easier for transcription to occur. In other words, histone acetylation typically lead to activation of gene expression.

    DNA methylation is when the DNA themselves are methylated (obviously, by an enzyme) at the cytosine pyrimidine ring. Methylated DNA may be physically harder for transcription factor to bind, hence inhibit gene expression. More importantly, methylated DNA regions are recognized by other proteins that will cover the region, recruit more enyzme to DEacetylate the histone proteins. This kind of chromatin remodeling causes the DNA to become less accessible to transcription factor access. As a result, DNA methylation is typically associated with gene silencing.

    Now that you know about histone acetylation and DNA methylation, let's talk about genomic imprinting. Genomic imprintingis basically an epigenetic phenomenon when certain genes are expressedin a parent-of-origin specific manner. For example, if you receivedthis gene from the mom, the gene is silenced; if you received it fromthe dad, then the gene is activated and expressed, even if the sequenceof the gene itself is exactly the same between the mom and the dad. (This could also go the other way, maternal allele is expressed,paternal allele is silenced).

    2009-02-08 03:13:15 補充:

    (answer continued here...)

    Since epigenetic phenomenon are not due to differences in DNA sequence, the differential expression results from processes such as histone acetylation and DNA methylation.

    2009-02-08 03:13:24 補充:

    To give you a simple example, for an imprinted gene due to DNA methylation, inside the sperm cells and the egg cells all methylation marks are erased (demethylated). But in the sperm cell, this gene region will always be methylated while in the egg cell this region is never methylated.

    2009-02-08 03:13:40 補充:

    As a result, when the sperm fertilize the egg, the paternal copy of the gene is methylated and silenced, but the maternal copy of the gene is not methylated and thus expressed. You can imagine similar things to happen with histone acetylation.

    2009-02-08 03:13:45 補充:

    This is how genomic imprinting is connected with histone acetylation and DNA methylation.

    I think this might be a lot for you to digest, but let me know if you have more questions.

    Source(s): I'm a graduate student in Genetics in the US
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