Chargaff's bases

by **CurlyQe** » Fri Jul 21, 2006 1:01 am

Chargaff said that A=T and C=G, approximately. But the numbers for A do not exactly match for T and the same for C and G. Are these mutations? Or are Chargaff's numbers not ver accurate?

by **SU_reptile** » Fri Jul 21, 2006 9:10 am

As far as I remember from high school there are derivatives of bases that may be complementary to the original ones. What's more, in tRNA first or third base (I don't remember exactly) in anticodon have some toleration for other bases.
Besides, what do you mean, by

the numbers for A do not exactly match for T and the same for C and G

. What numbers? Where did you get those information from? It may be true but what is a source of your uncertainty?

by **arul** » Fri Jul 21, 2006 9:20 am

Hi mates,

Chargaff's rules state that DNA from any cell of all organisms have a 1:1 ratio of pyrimidine and purine bases and more specifically that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. This pattern is found in both strands of the DNA.

by **CurlyQe** » Fri Jul 21, 2006 1:10 pm

But if I remember correctly, that 1:1 ratio is not completely 1:1 there is a fractional difference between the bases that chargaff says have a 1:1 ratio... ack! If only I can find those numbers again!

by **victor** » Fri Jul 21, 2006 1:30 pm

how about this:
Just imagine there's a deletion in one of the DNA bases. so, now the remaining bases will be mispaired won't they??
Ex: Before deletion
---ATTGCC---
---TAACGG---

After deletion
---ATGCCA---
---TAACGG---

Now, you can see that because of this kind of mutation (deletion, insertion, duplication, etc.), there'll be no exact number if A=T and C=G :lol:

by **CurlyQe** » Fri Jul 21, 2006 7:51 pm

Aha. So they ARE mutations. Thanks!

by **sdekivit** » Fri Jul 21, 2006 8:00 pm

the rule is pure theoretical and represents the most ideal case with no mutations in the DNA as explained before. It is just a rule for how correct DNA is arranged.