tailieunhanh - Biochemistry, 4th Edition P101

Biochemistry, 4th Edition P101. 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 the Structure of Ribosomes and How Are They Assembled 963 rRNAs The rRNAs of E. coli are encoded by a set of seven opérons Figure . Each of these operons is transcribed into a 30S rRNA precursor that includes several tRNAs. RNase III and other nucleases cleave these precursors to generate 23S 16S and 5S rRNA as well as several tRNAs that are unique to each operon. Transcription of rRNA genes accounts for 80 to 90 of total cellular RNA synthesis. Ribosomal RNAs show extensive potential for intrachain hydrogen bonding and assume secondary structures reminiscent of tRNAs although substantially more complex see Figures and . About two-thirds of rRNA is double-helical. Double-helical regions are punctuated by short single-stranded stretches generating hairpin conformations that dominate the molecule four distinct domains can be discerned in the secondary structure of 16S rRNA and six in 23S rRNA. The three-dimensional structures of both the 30S and 50S ribosomal subunits show that the general shapes of the ribosomal subunits are determined by the conformation of the rRNA molecules within them. Figure illustrates the three-dimensional structure of 16S rRNA within the 30S subunit. The overall form of the 30S structure is essentially that of the rRNA compare Figures and . The same relationship is true for the 23S plus 5S rRNA and the large ribosomal subunit compare Figures and . Ribosomal proteins serve a largely structural role in ribosomes their primary function is to brace and stabilize the rRNA conformations within the ribosomal subunits. Ribosomes Spontaneously Self-Assemble In Vitro Ribosomal subunit self-assembly is one of the paradigms for the spontaneous formation of supramolecular complexes from their macromolecular components. If the individual proteins and rRNAs composing ribosomal subunits are mixed together in vitro under appropriate conditions of pH and ionic strength spontaneous selfassembly .

• 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