分子遗传学英文课件WORD版.doc

1-Structures of gene, promoter and enhancer Genotype: The genetic constitution of an organism. Phenotype: The appearance or other characteristics of an organism, resulting from the interaction of its genetic constitution with the environment. Gene: The segment of DNA involved in producing a polypeptide chain. An eukaryotic genes includes a promoter region, regions preceding (5 UTR) and following (3 UTR) the coding region as well as intervening sequences (introns) between individual coding segments (exons). Promoter region, responsible for the binding of RNA polymerase and for the subsequent initiation of transcription The transcriptional initiation site, where the transcription starts and will receive a “cap” of modified (methylated) nucleotides soon after it is transcribed. The translation initiation site (ATG), where the translation starts. The sequence between the transcription initiation site and translation initiation site is the 5’ untranslated region (5’UTR, part of the first exon), which can determine the rate at which translation is initiated. Exons, the region of DNA that codes for a protein. Introns, the intervening sequences that do not coding for amino acid sequence. The translation termination codon, TAA, which becomes UAA in the mRNA. The ribosome dissociates at this codon, and the protein is released. 3’ untranslated region, part of last exon, containing the sequence AATAAA, which is needed for polyadenylation (addition of a “tail” of about 200-300 adenylate residues on the RNA transcript). This polyA tail 1) confers stability on the mRNA, 2) allows the mRNA to exit the nucleus, and 3) permits the mRNA to be translated into protein. The PolyA tail is inserted into the RNA about 20 bases downstream of the AAUAAA sequence. Transcription termination sequence, transcription continues beyond the AATAAA site for about 1000 nucleotides before being terminated. cDNA: A single-stranded DNA complementary to an RNA, synthesized from it by reverse transcription