DNA Replication?

Question

A significant diff. btw/ eukaryotic and prokaryotic DNA is the presence of methylation of the prokaryotic DNA. What is the purpose of the methylation?

Answer 1

Many organisms have DNA methylation. Not just prok. In eukaryotes DNA methylation is usually cytosine methylation whereas in prokaryotes it's usually other bases, mainly adenine.

the purpose is different in different organisms. in prokaryotes, DNA methylation is mainly a defense mechanism. Foreign DNA, such as from bacteriophages (viruses) are not methylated. The bacteria make enzymes (restriction endonucleases) that can digest DNA, but in many cases they will not digest methylated DNA. The genome of the bacteria will be protected while the foreign DNA will be digested.


TO THE PERSON ABOVE ME: if you are just going to copy and paste from wikipedia, you should at least tell the asker that's what you did or provide a link.

Answer 2

Depends if it's a mammal, plant, etc, but DNA methylation involves the addition of a methyl group to DNA — for example, to the number 5 carbon of the cytosine pyrimidine ring.

DNA methylation at the N5 position of cytosine has been found in every vertebrate examined. In humans, approximately 1% of DNA bases undergo DNA methylation. In adult somatic tissues, DNA methylation typically occurs in a CpG dinucleotide context; non-CpG methylation is prevalent in embryonic stem cells.

In plants, cytosines are methylated both symmetrically (CpG or CpNpG) and asymmetrically (CpNpNp), where N can be any nucleotide.

The methylation status of specific cytosines can be determined using methods based on bisulfite sequencing.

DNA methylation is the addition of a methyl group to a piece of DNA. This can silence the gene resulting in loss of gene function.

It should be noted that some organisms, such as fruit flies, have virtually no DNA methylation.