Translation Translation The final product of gene expression

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. m. RNA transcribed from genomic DNA Transfer RNA (t. RNA) to transport amino acids Ribosome to “read” m. RNA, align amino acids attached to t. RNA and create the peptide bonds between adjacent amino acids

Ribosome Two subunits composed of protein and ribosomal RNA (r. RNA) The r. RNA is a structural component of the ribosome subunits

The Ribosome (Eukaryote) 40 S 18 S RNA + 33 proteins 80 S 60 S 28 S RNA + 49 proteins

t. RNAs 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)

t. RNA

t. RNA The amino acid attaches to the 3’ end of the t. RNA can base pair with the codon in m. RNA at the anticodon on the t. RNA

Charging t. RNA with an Amino Acid An individual t. RNA is specific for a single amino acid. (There at least 20 different t. RNAs) Charging is the process of covalently attaching an amino acid to the t. RNA Charging is accomplished by aminoacyl t. RNA 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 m. RNA in the ribosome is aligned to set the reading frame Elongation—Charged t. RNAs 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. m. RNA is not modified 3. Transcription and translation take place in the same area

Prokaryotes vs. 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 m. RNA 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 AAt. RNA to the A site in the ribosome Erythromycin: Blocks the movement of the ribosome down the m. RNA Streptomycin: Blocks formation of the initiation complex and causes miscoding Rifamycin: Blocks transcription by blocking binding of RNA polymerase