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abp, base pairs.

abp, base pairs.

an RNA-DNA hybrid. The RNA strand is broken down in alkaline conditions, yielding a single-stranded molecule of DNA. The DNA polymerase reaction affords a complementary or copy strand of DNA (cDNA), which on fusion of a promotor sequence can be attached to a transport vector. Figure 4.5 depicts these reactions.

If the amino acid sequence of a protein (and, hence, the codon sequence) is known, automated synthesis of DNA through chemical or enzymatic means represents a third way that genes can be engineered. This method is useful only for relatively small proteins. In principle, for the preparation of a genomic library, the cellular origin of the DNA is not an issue, whereas the cellular origin of mRNA is central to the preparation of a cDNA library. Therefore, genomic libraries vary from species to species but not from tissue to tissue within that species. cDNA varies with tissue and the developmental stages of cells, tissues, or species. Another important distinction is that the fragment of DNA from eukaryotic chromosomes will contain exons (protein-coding segments) and introns (noncoding segments between exons), whereas in cDNA, the introns are spliced out.

mRNA

DNA Synthesis, mRNA as Matrix

RNA-DNA Hybrid

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