TAILIEUCHUNG - Biochemistry, 4th Edition P41

Biochemistry, 4th Edition P41. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | What Is a DNA Library 363 heterologous probes because they are not derived from the homologous same organism. Problems arise if a complete eukaryotic gene is the cloning target eukaryotic genes can be tens or even hundreds of kilobase pairs in size. Genes this size are fragmented in most cloning procedures. Thus the DNA identified by the probe may represent a clone that carries only part of the desired gene. However most cloning strategies are based on a partial digestion of the genomic DNA a technique that generates an overlapping set of genomic fragments. This being so DNA segments from the ends of the identified clone can now be used to probe the library for clones carrying DNA sequences that flanked the original isolate in the genome. Repeating this process ultimately yields the complete gene among a subset of overlapping clones. cDNA Libraries Are DNA Libraries Prepared from mRNA cDNAs are DNA molecules copied from mRNA templates. cDNA libraries are constructed by synthesizing cDNA from purified cellular mRNA. These libraries present an alternative strategy for gene isolation especially eukaryotic genes. Because most eukaryotic mRNAs carry 3 -poly A tails mRNA can be selectively isolated from preparations of total cellular RNA by oligo dT -cellulose chromatography Figure . DNA copies of the purified mRNAs are synthesized by first annealing short oligo dT chains to the poly A tails. These oligo dT chains serve as primers for reverse transcriptase-driven synthesis of DNA Figure . Random oligonucleotides can also be used as primers with the advantages being less dependency on poly A tracts and increased likelihood of creating clones representing the 5 -ends of mRNAs. Reverse transcriptase is an enzyme that synthesizes a DNA strand copying RNA as the template. DNA polymerase is then used to copy the DNA strand and form a double-stranded duplex DNA molecule. Linkers are then added to the DNA duplexes rendered from the mRNA Known amino acid sequence

• Sinh học
• Nền tảng của hóa sinh học
• trao đổi chất protein
• RNA trao đổi chất
• nguyên tắc của hóa sinh
• Axit amin
• công nghệ DNA