Question

8) You have extracted DNA from two different organisms. In the purification process, you find that the two test tubes have lost their identifying labels. The sequences of DNA are:

Sample 1: TCC CTA TGC CCG AGG GAT ACG GGC

Sample 2: CGA TCT TAA CCC GCT AGA ATT GGG

The only other piece of information you have is the corresponding amino acid sequence of a particular protein for both organisms. Organism I has ala-arg-ile-gly and organism II has ala-arg-ile-pro.

a) What amino acid sequence corresponds with which nucleic acid sequence?

b) For each sample of DNA, which is the sense strand?

Answer 1

Ans 1: Let us take the first sample which has a sequence of TCC CTA TGC CCG AGG GAT ACG GGC and its complementary strand is AGG GAT ACG GGC TCC CTA TGC CCG. Now for second sequence which has a sequence of CGA TCT TAA CCC GCT AGA ATT GGG and its complementary strand is GCT AGA ATT GGG CGA TCT TAA CCC. Now organism 1 has ala-arg-ile-gly, ala is coded by GCT, arg is coded by AGA, ile is coded by ATT and Gly is coded by GGG. So from the data we can say that the sample 2 is of organism 1 and sample 1 is of organism 2 because all the corresponding amino acids and its coding sequence matched.

Ans 2: A sense strand, or coding strand, is the segment within double-stranded DNA that carries the translatable code in the 5′ to 3′ direction, and which is complementary to the antisense strand of DNA, or template strand, which does not carry the translatable code in the 5′ to 3′ direction. So from the above described answer we can evaluate that the sense strand for Sample 1 is AGG GAT ACG GGC TCC CTA TGC CCG and for Sample 2 the sense strand is GCT AGA ATT GGG CGA TCT TAA CCC because these two sequences are actually coding for the amino acids and the given sequences in the question is just used as a template at the time of transcription.