基因表达及调控2.ppt

Synthesis and Processing of the Protein The Role of the Ribosome in Protein Synthesis Ribosomes coordinate protein synthesis by placing the mRNA, aminoacyl-tRNAs and associated protein factors in their correct positions relative to one another. Components of ribosomes, including the rRNAs, catalyze at least some of the chemical reactions occurring during translation. Regulation of translation initiation Global regulation, which involves a general alteration in the amount of protein synthesis occurring, with all mRNAs translated by the cap mechanism being affected to a similar extent. Transcript-specific regulation involves mechanisms that act on a single transcript or a small group of transcripts coding for related proteins. Elongation of translation Termination of translation 蛋白质的翻译后加工 Protein folding Not all proteins fold spontaneously in the test tube. In cells, folding is aided by molecular chaperones（分子伴侣）. Molecular chaperones do not specify the tertiary structure of a protein, they merely help the protein find that correct structure. 有些真核基因在原核细胞 中表达不能正确折叠。 Processing by chemical modification Acetylation, Glycosylation, phosphorylation Over 150 different modified amino acids have been documented in different proteins Intein splicing Most are known in bacteria and archaea but there are also examples in lower eukaryotes. In a few cases there is more than one intein in a single protein. Protein Degradation In eukaryotes, most breakdown involves a single system, involving ubiquitin and the proteasome. Regulation of Genome Expression Genome ≠ Transcriptome Two levels of gene regulation 1. 是否表达 2. 表达量及表达后修饰 基因表达调控的关键步骤是转录启始， 即决定一个基因是否表达。 基因组表达活性的调节 一过性的表达活性改变 永久或半永久性的表达改变 （underlie cellular differentiation ） 一过性的表达改变 主要表现为对外界刺激的反应 单细胞生物 stimuli: nutrient availability 多细胞生物 stimuli: hormones, growth factors, and related compounds 外来信号物质作用于细胞的方式 直接的 穿过细胞膜进入细胞内发挥作用。