The following is a portion of an mrna sequence: 3'-aucgucaugcaga-5' part a during transcription, was the adenine at the left-hand side of the sequence the first or the last nucleotide added to the portion of mrna shown? a. the first b. the last part b write out the sequence of the dna duplex that encodes this mrna segment.

Part A: Adenine at the 3'-end would be the last nucleotide added to the portion of mRNA.

Part B: Sequence of DNA duplex would be

5'-TAGCAGTACGTCT-3'

3'-ATCGTCATGCAGA-5'

Transcription is the process by which nucleotide sequence of template strand of the DNA is copied into the nucleotide sequence of RNA with the help of RNA polymerase enzyme.

This enzyme read the template strand of DNA in 3' to 5' direction and create a complementary RNA in 5' to 3' direction. It is because RNA polymerase can add nucleotide only to the 3' end of the RNA.

The nucleotide sequence of RNA produced is complementary to the DNA template strand and is exactly same as that of non-template or coding strand. The only difference is the presence of uracil (in RNA) in place of thymine (in DNA).

Hence, the nucleotide sequence of DNA template strand of given mRNA would be 5'-TAGCAGTACGTCT-3' and that of the non-template strand would be 3'-ATCGTCATGCAGA-5'.

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step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.