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Transcription/Translation

Transcription/Translation. There are two major steps in protein synthesis; the first is transcription and the second is translation. Key Defintions :.

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Transcription/Translation

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Presentation Transcript

  1. Transcription/Translation There are two major steps in protein synthesis; the first is transcription and the second is translation.

  2. Key Defintions: Before we start, it’s important to understand the meanings of the following: -RNA polymerase: An enzyme that transcribes DNA into mRNA, using complimentary bases (A-U, T-A, G-C, C-G)-messenger RNA (mRNA): the result of transcription; ribosomes translate the mRNA into a protein.-transfer RNA (tRNA): delivers amino acids to ribosomes.- ribosomal RNA (rRNA): RNA binds with protein to form ribosomes.

  3. More… Template strand: the DNA strand that is used by RNA polymerase in transcription.Coding strand: DNA strand that is not used in transcription. It has the same sequence as mRNA but instead of A complimenting T, it compliments U.Promoter: DNA that is bound by RNA polymerase in the upstream of the gene.

  4. Transcription: Three Steps • Initiation • Elongation • Termination http://www.dadamo.com/wiki/transcript.jpg Check out link for a diagram of these steps.

  5. Initiation Firstly, the RNA polymerase binds to the promoter of the DNA. This results in the opening of the double-helix. This is essential in order for the cell to create the proper polypeptide. This happens in the upstream area of the gene – which means it’s adjacent to the beginning of the gene.

  6. Elongation Begins when RNA polymerase has bound to the promoter. The synthesis of mRNA occurs along the 5’ to 3’ cap. RNA polymerase joins the ribonucleotides using one strand of the DNA, called the template strand.

  7. Termination RNA polymerase will pass the gene once mRNA has been synthesized, and as it does it will receive a signal from the terminator sequence to stop transcribing. mRNA is released along with RNA polymerase.

  8. Posttranscription In eukaryotic cells, changes are made to the primary transcript. A 5’ cap is added to ensure that the mRNA is safe from nucleases and phosphatases, since it is about to leave the nucleus and enter the cytoplasm. Also, 200 adenine ribonucleotides are added to the 3’, thanks to poly-A polymerase. Introns and extrons are found within the gene of the DNA and before the primary transcript exits the nucleus, the introns are removed, by spliceosomes. The spliceosomes then proceed to put the exons together.

  9. TRANSLATION

  10. Initiation • The ribosome subunits recognize a certain sequence on mRNA and bind to them. There is a large ribosome subunit, which contains the A and P sites, as well as a small subunit. • The ribosome moves past three nucleotides at a time. Translation occurs once the start codon (AUG) has been read. • Three nucleotides, also known as one codon, code for an amino acid.

  11. Elongation • the tRNA will deliver the amino acid when AUG is in the P site. • While the start codon is in the P site, the next one is located in the A site. The tRNA will deliver the next amino acid, and a peptide bond between the two amino acids is formed. Then the amino acid that was in the A site will go to the P site, and a new codon will arrive in the A site as the process will repeat itself. • Elongation ends where codon stops coding for an amino acid and becomes the “stop” codon.

  12. Termination • The stop codon does not code for an amino acid like the rest, therefore there are no more tRNAs. • The ribosome falls off mRNA and the polypeptide chain is released. • Sugars and phosphates are added to amino acids at times for glycosylation, etc… (Di Giuseppe et al. 2003)

  13. References Di Giuseppe, Maurice, Vavitsas, A., Ritter, Dr. Bob, & F., Douglas (2003). Biology 12. Canada: Thomson Nelson.

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