Base-pair matching

[DeathandTaxes]

Could someone explain to me what their procedure is for dealing with these types of problems?
Is "antisense" the molecule that runs along with this one?

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[flyingwarthog]

answer=C
the question is asking for the strand with the complementary sequence to the mRNA sequence given. i think they use the word "antisense" to imply that the complementary strand won't be read by a ribosome; the sense strand (mRNA in this case) will be read by a ribosome. the procedure is simple: pick the strand that has the complementary sequence. to do this, you just need to determine the base pair that would match with the base pair in the given mRNA strand. for example, the first nucleotide in the mRNA is C, which we know matches with G. the second nucleotide is G, which matches with C. the third nucleotide is A, which matches with U. two important things to remember for questions like these are:

1) get the directionality correct, which means that the complementary sequence must have the opposite directionality (remember that DNA and RNA strands are antiparallel - if you don't know what that means then read a genetics textbook.)

2) remember that there is no thymine in RNA. anything that would be a thymine is a uracil instead.

 

[flyingwarthog]

clarification: I said DNA and RNA are antiparallel. RNA is usually single stranded, so antiparallel generally doesn't apply to RNA as it does to DNA. RNA can become double stranded if it has an inverted repeat (like in tRNA and some transcription termination mechanisms).

 

[StIGMA]

clarification: I said DNA and RNA are antiparallel. RNA is usually single stranded, so antiparallel generally doesn't apply to RNA as it does to DNA. RNA can become double stranded if it has an inverted repeat (like in tRNA and some transcription termination mechanisms).

RNA is most often single stranded but still folds on itself, such as in ribosomal RNAs (check a crystal structure, tRNAs, and in most mRNAs). "falling in" on itself is energetically favorable, so the RNA folds will be compacted on itself. There does not need to be an inverted repeat/stem loop (although that structure is often bound by specific proteins depending on the conserved sequence). Some basic images - http://doudna.berkeley.edu/translation.html

While the above are not technically anti-parallel, specific cellular RNAs when processed are antiparallel, such as microRNAs.

 

[Czarcasm]

Antisense is just a nickname for the template DNA strand. The way it was presented to me in molecular genetics was that it's "antisense" because it's strand is jibberish and only acts as a template so that the mRNA strand can have the complementary DNA (which makes 'sense'). This is what's read and translated by the ribosome. Also, the non-template DNA strand is the sense strand because it has the relevant coding info for the protein. Through complementary rules, via replication machinery, we are able to synthesize an antisense complementary DNA strand using the sense DNA template. This antisense complementary template then serves as a template to produce the mRNA, which has the relevant information needed for translation. You can think of the antisense strand as an intermediate I guess, since synthesis occurs only by base pairing due to complementarity.

Also, transcription (like replication) occurs anti-parallel and so, you want to make sure your DNA template has opposite directionality and is complementary using the base pairing rules.