翻译与蛋白质.pdf

1 Chapter 13 Translation and Proteins 翻译与蛋白质 Translation 翻译 Defined as the polymerization 聚合 of amino acids 氨基酸 into a polypeptide 多 肽 chain Occurs at on ribosomes 核糖体 using mRNA templates tRNAs covert triplet codons into specific amino acid sequence by base pairing with anticodon 反密码子 Ribosome Structure About 10 000 ribosomes in growing E coli cell can be more Bacterial ribosomes about 250 nm across Made of rRNAs and ribosomal proteins Two subunits 亚基 large and small Eukaryotes and prokaryotes generally similar but different enough 70S vs 80S etc tRNA Structure 75 90 nucleotides in size General structure highly conserved in prokaryotes and eukaryotes Transcribed as larger precursor processed Nucleotides removed Nucleotides added Bases modified many modified bases present tRNA Structure Cloverleaf model 三叶草模型 Convenient to show major loops and base pairing Actually more L shaped 3 loops or arms D arm T U arm anticodon arm 5 end is G 3 end is always CCA Amino acid attached to the terminal adenylate 腺苷 酸 Some of these nucleotides can be added added posttranscriptionally 转录后地 2 tRNA Cloverleaf 反密码子臂反密码子臂 The Many Factors of Protein Synthesis Each phase has its own set of factors Phases of Translation Three phases Initiation Small and large subunits charged initiator tRNA GTP Mg and several initiation factors Ifs First codon is AUG Shine Dalgarno box AGGAGG in E coli at 10 to AUG Ends with the addition of the large subunit Elongation Termination Polyribosomes 多聚核糖体 Polysomes Multiple ribosomes bound to a single mRNA Increase overall rate of protein production One mRNA simultaneously directs the synthesis of multiple copies of a polypeptide Polysomes 多聚体 Found in eukaryotes and prokaryotes These examples are from rabbit reticulocytes and midgefly salivary glands Note polypeptide chain lengthens as ribosomes progress along mRNA Eukaryotic Translation Larger ribosomes larger rRNAs for ribosomal proteins More factors mRNAs have longer half life Hours or longer vs minutes in prokaryotes Short recognition sequence surrounds initiation AUG ACCAUGG Kozak box Initiation methionine 蛋氨酸 not formylated 甲 酰化 3