Fvj

Reverse transcriptase

Reverse transcriptase

Poly A tail 3' mRNA

3' mRNA

tttt 5' DNA primer (oligo dT)

Reverse transcription

Poly A tail 3' mRNA

3' mRNA

tttt 5' DNA primer (oligo dT)

When synthesis is completed, the mRNA is removed, leaving single-stranded cDNA.

tttt 5' cDNA

DNA polymerase uses the cDNA as a template to make a complementary DNA strand.

16.8 Synthesizing Complementary DNA Gene libraries that include only genes transcribed in a particular tissue at a particular time can be made from complementary DNA. cDNA synthesis is especially useful for identifying mRNAs that are present only in a few copies, and is often a starting point for gene cloning.

an appropriate base sequence for the gene. With this sequence as a starting point, we can add other sequences, such as codons for translation initiation and termination and flanking sequences for transcription initiation, termination, and regulation. Of course, these noncoding DNA sequences must be the ones actually recognized by the host cell if the synthetic gene is to be transcribed. It does no good to have a prokaryotic promoter sequence near a gene if that gene is to be inserted into a yeast cell for expression. Codon usage is also important: as we have seen, many amino acids are encoded by more than one codon, and different organisms stress the use of different synonymous codons.

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Essentials of Human Physiology

Essentials of Human Physiology

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