DNA methylation (1 Viewer)

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Monique

Staff Emeritus
Science Advisor
Gold Member
4,069
62
I heard that a methylated cytosine converts into a thymine by the following mechanism:


The metC during the replication of DNA is place w/ an A opposite, and after the second replication you get what looks like a C to T transition.


But isn't the metC to T transition caused by the de-amination of the metC?
 

Another God

Staff Emeritus
Gold Member
975
3
I have just been studying DNA repair mechanisms in E. Coli, and what I got out of that was that after replication of DNA, over a period of time, all of the A's get methylated, and that is all. I got the impression that C's, G's and T's are never methylated. Maybe I only got that impression though because I am only looking at one area. Biochemistry likes to make lots of different situations where things go differently.

Does this sound like I might have anything useful to offer? Or am I completely off the track u are interested in?

(I am quite up to date now on Photoreactivation repair, Excision repair, Recombination Repair and SOS repair...)
 

Another God

Staff Emeritus
Gold Member
975
3
Oh yeah, I get what u mean now. U are saying that the methylation occurs on the 5-Carbon of C, and somewhere in the reaction, the Amine group is lost, resulting in a chemical change from C to T (rather than an actual base change where the C gets detached, and a T get attached.)

well, it seems possible (I know nothing about it directly)

2 thoughts:

First: Perhaps this occurance gives the average cell a good evolutionary reason to onyl Methylate Adenines...?

Second: Why is the A placed opposite the C in the first place? Is that just an error? And if that was to even happen, I can't see how the H binding interaction between an A and a C would cause the C to deaminate. Unless this is catalysed by some enzyme (a strange thing to be catalysed), it seems like a strange sort of random mutation to occur.
 

iansmith

Staff Emeritus
Science Advisor
Gold Member
1,345
2
Hi

Monique, it appears that you are that both explanations your given are the same but there seen to be missing information to the first explanation. Here how i learned in my advance genetic classes:

C spontaneoulsy deaminates to at a frequency of 10 ^-3 and it is normally repaired by Uracil DNA glycosylase (UDG). The problem is if C is methyated then 5-methyl U = T. UDG cannot repair the this because t is a normal DNA base pair. This mismatch appear on the mother/methylated strand and an A is inserted to the daughter/unmethylated strand. Ttherefore C is match with an A.

Another god your partly right about the A methylation. Methylation in E. coli occurs at a high frequency at A residues but still occurs on G, C and T but at very low frequency.

Also, even though association of the C and A does not make sense, DNA polymerase is not perfect and will mismatch base pair at a frequency ranging form 10^-6 to 10^-9. these mismatch can be repair by using enzyme that have for reference the mother/methylated strand. Also keep in mind that if DNA polymerase would be perfect there would be no mutation and no evolution.


Ian
 

Monique

Staff Emeritus
Science Advisor
Gold Member
4,069
62
Thank you both, that clears things up. Ian: may I ask about your background?
 

iansmith

Staff Emeritus
Science Advisor
Gold Member
1,345
2
I have a B. Sc in microbiology my undergrad project was to sequence a plasmid from H. ovis and i am starting my master in microbiology and have to sequence the hemoglobin receptor gene and study how H. ovis acquires Iron from hemoglobin.
 
Last edited:

Monique

Staff Emeritus
Science Advisor
Gold Member
4,069
62
Cool, so you are going to mutate the receptor? Btw, what is H. Ovis? A common bacteria?
 

iansmith

Staff Emeritus
Science Advisor
Gold Member
1,345
2
We migth knock out the Hm receptor if i have time. Histophilus ovis is not a common bacteria, it is member of the pasteurellaceae ( Hemophilus influenzae for example) and it is a sheep pathogen. Not much people are studying this bacteria.
 

Monique

Staff Emeritus
Science Advisor
Gold Member
4,069
62
Originally posted by iansmith
Not much people are studying this bacteria.
So why are you interested in it?
 

iansmith

Staff Emeritus
Science Advisor
Gold Member
1,345
2
Working with bacteria that are not common makes your research more interresting because everythings you do is pretty much new. I also took the project my supervisor gave me and i don't why he was interested by this bacteria.
 
Last edited:

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top