Biochemistry, 4th Edition P95. 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. | Problems 903 tective caps on the chromosome ends. DNA polymerases cannot replicate the extreme 5 -ends of chromosomes but a special polymerase called telomerase maintains telomere length. Telomerase is a ribonucleoprotein and its RNA component serves as template for telomere synthesis. How Are RNA Genomes Replicated Many viruses have genomes composed of RNA not DNA. DNA may be an intermediate in the replication of such viruses that is viral RNA serves as the template for DNA synthesis. This reaction is catalyzed by reverse transcriptase an RNA-dependent DNA polymerase. How Is the Genetic Information Shuffled by Genetic Recombination Genetic recombination is the exchange or incorporation of one DNA sequence with or into another. Recombination between very similar DNA sequences is called homologous recombination. Homologous recombination proceeds according to the Holliday model. The RecBCD enzyme complex unwinds dsDNA and cleaves its single strands. RecA protein acts in recombination to catalyze the ATP-dependent DNA strand exchange reaction. Procession of strand separation and re-pairing into hybrid strands along the DNA duplex initiates branch migration displacing the homologous DNA strand from the DNA duplex and replacing it with the ssDNA strand. RuvA RuvB and RuvC resolve the Holliday junction to form the recombination products. DNA replication is an essential component of both DNA recombination and DNA repair processes. Furthermore recombination mechanisms can restart replication forks that have halted at breaks or other lesions in the DNA strands. Transposons are mobile DNA segments ranging in size from several hundred base pairs to more than 8 kbp that move enzymatically from place to place in the genome. Can DNA Be Repaired Repair systems correct damage to DNA in order to maintain its information content. The most common forms of damage are 1 replication errors 2 deletions or insertions 3 UV-induced alterations 4 DNA strand breaks and 5 .
