分子生物学（张海红）CHAPTER14.pptVIP

Molecular biology course 4 primary components mRNAs tRNAs aminoacyl-tRNA synthetases ribosomes mRNA Only a portion of each mRNA can be translated. The protein-coding region of the mRNA consists of an ordered series of 3-nt-long units called codons that specify the order of amino acids. The protein coding region of each mRNA is composed of a contiguous, non-overlapping string of codons called an opening reading frame (ORF) . Each ORF begins with a start codon and ends with a stop codon. Structures of mRNA related with translation Prokaryotic mRNAs have a ribosome binding site that recruits the translational machinery Eukaryotic mRNA are modified at their 5’ and 3’ ends to facilitate translation. Ribosome binding site (RBS) or SD-sequence in prokaryotic mRNA, complementary with the sequence at the 3’ end of 16S rRNA. Once Eukaryotic mRNA uses a methylated cap to recruit the ribosome. Once bound, the ribosome scans the mRNA in a 5’-3’ direction to find the AUG start codon. Kozak sequence increases the translation efficiency. Poly-A in the 3’ end promotes the efficient recycling of ribosomes 4 primary components mRNAs tRNAs Aminoacyl-tRNA synthetases Ribosomes The are many types of tRNA molecules in cell (~50). Each tRNA molecule is attached to a specific amino acids (20) and each recognizes a particular codon, or codons (61), in the mRNA All tRNAs end with the sequence 5’-CCA-3’ at the 3’ end, where the aminoacyl tRNA synthetase adds the amino acid. The role of tRNA in protein synthesis tRNA Structure tRNA primary structure tRNA secondary structure tRNA tertiary structure tRNA function ——adapter Aminoacylation: The attachment of amino acids to tRNA Condon-anticodon interactions: The attachment of tRNA to mRNA tRNA primary structure Linear length: 74-90 nt (commonly 76) Modified bases: 5~10/tRNA Over