Why does adenine always pair with thymine and cytosine always pair with guanine when DNA is replicating?

Answer 1

Adenine and thymine forms 2 hydrogen bonds, while guanine and cytosine forms 3 hydrogen bonds.

Adenine does not pair with guanine or cytosine because its pairing with thymine makes these 2 DNA bases stable.

Adenine does not fit very well with guanine and cytosine because they would prefer to bond with 3 hydrogen bonds.

Adenine and guanine are purines, which have two organic rings and thymine and cytosine are pyridines, which have one organic ring. In order for the nucleotides to fit only purines can pair with pyridines.

Answer 2

The usual pairing is T with A and C with G. "Always" is a strong word; errors in transcription can occur, though they're rare. Also, Adenine and Thymine form 2 hydrogen bonds, while Guanine and Cytosine form 3 hydrogen bonds. Guanine and Cytosine bond with 3 hydrogen bonds, and would prefer to bond with each other. Also when they bond, they make the 2 DNA bases stable. This also happens with Adenine and Thymine, but with 2 hydrogen bonds and 2 DNA bases stable.

Answer 3

This principle is called Chargaff's rule. In double stranded DNA Thymine is always bound to Adenine while Cytosine is always bound with Guanine. Therefore the percentage of A will always equal the percentage of T and the percentage of G will always equal the percentage of C.

Take a hypothetical DNA molecule containing 20%T. This DNA will have 20%T, 20%A, 30%C and 30%G.

Answer 4

That is the way the DNA is formed. If This occurrence is messed up the way a human is formed will drastically be changed. This is how many genetic diseases occur.

Because pairing takes place between purine and pyrimidine

Answer 5

They tend to pair strongly that way because of the pattern of hydrogen bonds that they are capable of making with each other. However mistakes can happen and sometimes (less than once in a trillion pairings) it happens in a different way, which is one source of mutations.

Answer 6

Because purine pairs with pyrimidine

Answer 7

Yea man.