DNA replication question

[Guest MDin2006]

8o I know that codons and anticodons are always written as 5' -> 3', does that apply during DNA replication as well? That is, if a question asks what the complimentary sequence of ATAC is, is the answer TATG or GTAT?

[Guest MDin2006]

Also, do we have to know all 64 codons and what they stand for?

[Guest Kirsteen]

Hi there,

 

For your latter question, nope, you definitely do not need to memorize all 64 codons. Princeton Review, however, recommended that we learn the start and stop codons, the latter being the Us: UAA, UGA and UAG, if I am brushing the cobwebs away correctly.

 

Cheers,

Kirsteen

[Guest MDin2006]

Thanks Kirsteen.

 

Can anyone help me out with the first question I posted?

[Guest dfenst]

DNA Replication occurs in a 5' - 3' direction. That is, the parent strand is read 3' - 5' and the new copy - its complement - is 5' - 3'. The answer is TATG.

 

eg: if the parent strand is:

 

5'AATGCGT3'

3'TTACGCA5'

 

For this to replicate, the bottom piece is read from the 3' end, and so it's complement is 5'AATGCGT3'; and the top piece Okazakies along (also from the left) adding pieces of 5' - 3' segments.

[Guest pasoo]

hey actually, if they ask you what the complementary sequence of ATAC...it is in fact, GTAT and not TATG

 

The reason for this is pretty stupid, but its an important one...whenever u see a sequence that has no direction i.e. it does not specify whether 5 to 3` or 3`-5`, it is ALWAYS by convention stated in the 5 to 3` direction, without exception.

 

so, if they give u ATAC (which is thus in the 5-3 direction), then the complementary would be 3`-TATG-5`, OR just GTAT with no direction stated...

 

good question though, because this is on some of the mcat...make sure you get your polarities correct!