In the previous video, we discussed CpG islands. If you want to watch that video first, you can
click the link from the "i" button or find it in the description. Now, in this video, we'll be discussing
DNA methylation in detail.
Let's get straight to it. DNA methylation is the transfer of a methyl group from the same molecule
to the adenine and cytosine bases of DNA. This involves adding a methyl group to the DNA bases,
specifically adenine and cytosine. Methylation takes place on these two bases among the four
bases in DNA.
The transfer of the methyl group is mediated by an enzyme called DNA methyltransferases
(DNMTs). There are three types of DNMTs: DNMT1, DNMT3a, and DNMT3b.
DNMT1 has the specific function of maintaining the pattern of methylation within the cell. During
DNA replication, the newly synthesized DNA molecule is methylated at the same positions as the
parent DNA, thus maintaining the DNA methylation pattern. DNMT1 requires hemimethylated DNA
to work with.
DNMT3a and DNMT3b, on the other hand, are involved in de novo methylation. These enzymes
do not require hemimethylated DNA and can add methyl groups at new positions.
Now, let's dive into the mechanism of DNA methylation in detail. The process involves the
methylation of cytosine bases. DNA methyltransferases 3a or 3b act upon the cytosine base,
transferring a methyl group from the same molecule to the fifth position of the pyrimidine ring of
cytosine. This reaction converts the donor molecule of the methyl group, S-adenosyl methionine,
into S-adenosyl homocysteine.
The end result of this methylation reaction is 5-methylcytosine. However, cytosine is prone to
amination, which leads to spontaneous hydrolytic deamination. This results in the removal of an
amino group from the top of the pyrimidine ring and its substitution with oxygen. This hydrolytic
deamination can cause a single nucleotide mutation in the DNA molecule.
If this mutation is detected within the DNA molecule, it can be corrected by an enzyme called
thymine DNA glycosylase, which removes the thymine base in a G-G mismatch. This leaves an
abasic site, which is then repaired by AP endonucleases and DNA polymerase.
That's all about DNA methylation and the conversion of 5-methylcytosine into thymine. If you liked
the video, give it a thumbs up and make sure to subscribe to this channel. Thanks!
click the link from the "i" button or find it in the description. Now, in this video, we'll be discussing
DNA methylation in detail.
Let's get straight to it. DNA methylation is the transfer of a methyl group from the same molecule
to the adenine and cytosine bases of DNA. This involves adding a methyl group to the DNA bases,
specifically adenine and cytosine. Methylation takes place on these two bases among the four
bases in DNA.
The transfer of the methyl group is mediated by an enzyme called DNA methyltransferases
(DNMTs). There are three types of DNMTs: DNMT1, DNMT3a, and DNMT3b.
DNMT1 has the specific function of maintaining the pattern of methylation within the cell. During
DNA replication, the newly synthesized DNA molecule is methylated at the same positions as the
parent DNA, thus maintaining the DNA methylation pattern. DNMT1 requires hemimethylated DNA
to work with.
DNMT3a and DNMT3b, on the other hand, are involved in de novo methylation. These enzymes
do not require hemimethylated DNA and can add methyl groups at new positions.
Now, let's dive into the mechanism of DNA methylation in detail. The process involves the
methylation of cytosine bases. DNA methyltransferases 3a or 3b act upon the cytosine base,
transferring a methyl group from the same molecule to the fifth position of the pyrimidine ring of
cytosine. This reaction converts the donor molecule of the methyl group, S-adenosyl methionine,
into S-adenosyl homocysteine.
The end result of this methylation reaction is 5-methylcytosine. However, cytosine is prone to
amination, which leads to spontaneous hydrolytic deamination. This results in the removal of an
amino group from the top of the pyrimidine ring and its substitution with oxygen. This hydrolytic
deamination can cause a single nucleotide mutation in the DNA molecule.
If this mutation is detected within the DNA molecule, it can be corrected by an enzyme called
thymine DNA glycosylase, which removes the thymine base in a G-G mismatch. This leaves an
abasic site, which is then repaired by AP endonucleases and DNA polymerase.
That's all about DNA methylation and the conversion of 5-methylcytosine into thymine. If you liked
the video, give it a thumbs up and make sure to subscribe to this channel. Thanks!
