Question

A Drosophila gene produces an mRNA that begins with the following base sequence, 5’CAGUCUCCGACGU..... and ends in a poly-A tail. A full-length cDNA copy of this mRNA can be made and amplified by using one primer and the appropriate enzyme to make a first strand cDNA, then adding a second primer and another enzyme to make and amplify double-stranded DNA in a polymerase chain reaction. Which primers and enzymes should be used first and second? First primer First enzyme Second primer Second enzyme

A. 5’TTTTTTTTTTTTT3’ Reverse transcriptase 5’CAGTCTCCGACGT3'. Taq polymerase

B. 5’AAAAAAAAAAAAA3’ Reverse transcriptase 5’ACGTCGGAGACTG3'. Taq polymerase

C. 5’ACGTCGGAGACTG3' Reverse transcriptase 5’AAAAAAAAAAAAA3’ Reverse transcriptase

D. 5’CAGTCTCCGACGT3' Taq polymerase 5’TTTTTTTTTTTTT3’ Reverse transcriptase

E. 5’GTCAGAGGCTGCA3' Taq polymerase 5’TTTTTTTTTTTTT3’ Reverse transcriptase

Answer 1

An mRNA is converted into cDNA using the enzyme reverse transcriptase. This converts the mRNA into cDNA. mRNA having a poly-A tail means a long chai of A nucleotide. The primer s always complementary to the mRNA, so it will be of a long chain of T nucleotide. The mRNA 5’CAGUCUCCGACGU will be converted into cDNA with sequence 3' GTCAGAGAGGCTGCA 5'.

When mRNA is converted into cDNA. it is amplified using the enzyme Taq polymerase. The primer will be complementary to the cDNA which will have a sequence 5'CAGTCTCCGACGT 3'.

The answer is A.