第二章基因的结构.pptx

第二章 基因的结构;Coding region is a part of the gene that represents a protein sequence.Coding strand of DNA has the same sequence as mRNA.template strand of double-stranded DNA is the one that is used to specify the sequence of a complementary single strand of RNA. (The non-template strand is identical in sequence to the RNA product.)Transcription is synthesis of RNA on a DNA template.Translation is synthesis of protein on the mRNA template.;Transcription generates an RNA which is complementary to the DNA template strand and has the same sequence as the DNA coding strand. Translation reads each triplet of bases into one amino acid. Three turns of the DNA double helix contain 30 bp, which cide for 10 amino acids.;The tRNA cloverleaf has invariant and semi-invariant bases, and a conserved set of base pairing interactions.;Transfer RNA folds into a compact L-shaped tertiary structure with the amino acid at one end and the anticodon at the other end.;A space-filling model shows that tRNA Phe tertiary structure is compact. The two views of tRNA are rotated by 90o. ;The meaning of tRNA is determined by its anticodon and not by its amino acid.;A ribosome consists of two subunits.;A polyribosome consists of an mRNA being translated simultaneously by several ribosomes moving in the direction from 5’-3’ . Each ribosome has two tRNA molecules, one carrying the nascent protein, the second carrying the next amino acid to be added.;A ribosome assembles from its subunits on mRNA, translates the nucleotide triplets into protein, and then dissociates from the mRNA.;Protein synthesis occurs on polysomes. ;Messenger RNA is translated by ribosomes that cycle through a pool.;Overview: mRNA is transcribed, translated, and degraded simultaneously in bacteria.;Transcription units can be visualized in bacteria. ;Bacterial mRNA includes non-translated as well as translated regions. Each coding region has its own initiation and termination signals. A typical mRNA may have several coding regions