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Enzyme sử dụng mRNA như một bản mẫu để tạo ra một sợi DNA bổ sung. Những sợi mRNA là sau đó bị suy thoái, và enzyme có thể tiếp tục sản xuất một sợi ADN mới để phù hợp với sợi DNA đơn được thực hiện từ mRNA. Những chuỗi DNA phù hợp với trình tự của các exon được tìm thấy trong các gen trong bộ gen. | 280 PDQ BIOCHEMISTRY c in cDNA stands for complementary. The cDNA library is produced using that rather valuable and nonconformist enzyme reverse transcriptase. If you select one cell type and isolate the mRNA pool from that cell reverse transcriptase allows you to generate DNA sequences that match the blueprint sequences found in mRNA Figure 8-14 . The enzyme uses mRNA as a template to generate a complementary strand of DNA. The mRNA strand is then degraded and the enzyme can further produce a new strand of DNA to match the single DNA strand made from mRNA. These DNA sequences match the sequence of exons found in the genes within the genome. These duplex DNA molecules can be inserted into vectors it s a little more involved than the genomic library procedure and these can be cloned. You can purchase a cDNA library that contains DNA sequences coding for each protein expressed within a particular cell or tissue. The size of the DNA molecules within the cDNA library is considerably smaller than those DNA fragments found in a genomic library. It is estimated that there are about 104 different mRNA species and thus 104 proteins expressed within one cell type. If you are interested in a particular protein you must select a cDNA library from a cell or tissue that produces that protein. For example reticulocytes are a good choice for the study of globins. cDNA libraries can thus differ considerably from cell to cell and tissue to tissue. As well it is pos- T T T T T -----5 oligo dT Reverse Transcriptase Reverse Transcriptase RNase or Alkali Reverse Transcriptase DNA Polymerase Figure 8-14 The action of reverse transcriptase of viral origin takes mRNA and produces a complementary DNA strand. This hybrid mRNA-DNA can be attacked by RNase activity within the transcriptase to eliminate the original mRNA template. Following this the new DNA strand can be used to generate a complementary DNA strand that contains the original mRNA coding sequence. Thus cDNA that has a complete .
