Transcript PPT
Translation Translation The final product of gene expression is a polypeptide chain of amino acids whose sequence was prescribed by the genetic code. The Players 1. 2. 3. mRNA transcribed from genomic DNA Transfer RNA (tRNA) to transport amino acids Ribosome to “read” mRNA, align amino acids attached to tRNA and create the peptide bonds between adjacent amino acids Ribosome Two subunits composed of protein and ribosomal RNA (rRNA) The rRNA is a structural component of the ribosome subunits The Ribosome (Eukaryote) 40S 18S RNA + 33 proteins 80S 60S 28S RNA + 49 proteins tRNA tRNAs are small, extremely stable RNA structures shaped like a cloverleaf due to internal base pairing They are almost identical in both prokaryotes and eukaryotes They contain a number of posttranscriptional modifications, including non-traditional bases (other than (A, U, G and C) tRNA tRNA The amino acid attaches to the 3’ end of the tRNA tRNA can base pair with the codon in mRNA at the anticodon on the tRNA Charging tRNA with an Amino Acid An individual tRNA is specific for a single amino acid. (There are at least 20 different tRNAs) Charging is the process of covalently attaching an amino acid to the tRNA Charging is accomplished by aminoacyl tRNA synthetases, each of which is specific for an amino acid. Prokaryotes vs. Eukaryotes The process is essentially the same, but somewhat more complicated in eukaryotes. What I am showing you is the process for prokaryotes, but at the end I’ll talk a little bit about eukaryotes. Steps in Translation 1. 2. 3. Initiation—the two subunits of the ribosome come together and the start codon on the mRNA in the ribosome is aligned to set the reading frame Elongation—Charged tRNAs attach and peptide bonds form between the amino acids Termination Prokaryotes vs. Eukaryotes Prokaryotes vs. Eukaryotes Prokaryotes: 1. Translation takes place directly after transcription 2. mRNA is not modified 3. Transcription and translation take place in the same area 5’ 3’ Prokaryotes vs. Eukaryotes Eukaryotes: 1. Transcript is modified before leaving the nucleus (5’ cap and 3’ poly-A tail) 2. Modifications increase translation efficiency and lifespan of the mRNA 3. Translation takes place on ribosomes located in the rough endoplasmic reticulum (translation is physically separated from transcription) Eukaryotes Prokaryotes vs. Eukaryotes Influence on gene expression forms the basis of function in many antibiotics. The purpose is to impair function in the prokaryote without disrupting function in eukaryotes. Antibiotics 1. 2. 3. 4. Tetracycline: Blocks attachment of the AA-tRNA to the A site in the ribosome Erythromycin: Blocks the movement of the ribosome down the mRNA Streptomycin: Blocks formation of the initiation complex and causes miscoding Rifamycin: Blocks transcription by blocking binding of RNA polymerase