RNA/DNA Sequence Notation: 5'->3', 3'->5'... Does it matter?

[oneirologist]

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Hi all,

When a question asks for the DNA/RNA sequence that would complement/hybridize with a given sequence, does it matter whether the 5' or 3' end is listed first as long as the right nucleotides are matched when the two sequences are antiparallel?

i.e. What DNA sequence would complement: 5'-ATTGCA-3'?

a. 3'-TAACGT-5'
b. 5'-TGCAAT-3'

which are the same, just switched around based on whether we are listing the 5' or 3' end first. I know convention is that we read DNA 5' to 3', but just wondering if there is such a distinction on the MCAT?

Thanks!

 

[justadream]

No, pretty sure it doesn't matter.

 

[csx]

.

 

[Czarcasm]

Hi all,

When a question asks for the DNA/RNA sequence that would complement/hybridize with a given sequence, does it matter whether the 5' or 3' end is listed first as long as the right nucleotides are matched when the two sequences are antiparallel?

i.e. What DNA sequence would complement: 5'-ATTGCA-3'?

a. 3'-TAACGT-5'
b. 5'-TGCAAT-3'

which are the same, just switched around based on whether we are listing the 5' or 3' end first. I know convention is that we read DNA 5' to 3', but just wondering if there is such a distinction on the MCAT?

Thanks!

Nope, either answer is acceptable. As long as you realize the polarity of DNA and how mRNA and DNA are synthesized in an antiparallel fasion (with opposing polarity), then you'll be good to go. More than likely, they'll have it oriented in the 5' to 3' direction to avoid hinting people that the polarity is different, but regardless of what answer choice they present, it means the same thing.

 

[kraskadva]

Hi all,

When a question asks for the DNA/RNA sequence that would complement/hybridize with a given sequence, does it matter whether the 5' or 3' end is listed first as long as the right nucleotides are matched when the two sequences are antiparallel?

i.e. What DNA sequence would complement: 5'-ATTGCA-3'?

a. 3'-TAACGT-5'
b. 5'-TGCAAT-3'

which are the same, just switched around based on whether we are listing the 5' or 3' end first. I know convention is that we read DNA 5' to 3', but just wondering if there is such a distinction on the MCAT?

Thanks!

Well... technically either is correct, so long as they're notated properly (5' & 3' labeled)
However, IRL and on the MCAT you will only see 5' -> 3' (both in question stems and in answer choices).
So get used to reading backwards...
The MCAT won't ask you to write out the answer, only to pick it. And you need to be able to do that quickly.