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14 Cards in this Set
- Front
- Back
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Transcription ~ Step 1 |
the initiation of transcription commences when the RNA polymerase binds to the promoter region of the gene to be transcribed. At this point, the DNA is unwound and the double helix is disrupted. |
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Transcription ~ Step 2 |
RNA polymerase moves past the promoter until it reaches the start sequence of the gene to be transcribed. |
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Transcription ~ Step 3 |
a complementary RNA strand is synthesized in the direction of 5' to 3', using one strand of DNA as a template. This step is known as elongation. The complement of adenine in RNA is uracil. |
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Transcription ~ Step 4 |
once the terminator sequence is reached by the RNA polymerase, transcription ceases. The mRNA is separated from the DNA and the RNA polymerase falls off the DNA molecule, constituting termination of transcription. The DNA molecule reforms its double-helical shape. |
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Transcription ~ Step 5 |
the mRNA at this point is not in final form. Post transcriptional modifications need to be made. A cap is added to the 5' end and a poly-A tail is added to the 3' end by the enzyme poly-A polymerase. |
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Transcription ~ Step 6 |
introns (noncoding regions) are cut out of the primary transcript by particles known as spliceosomes. The spliceosomes then rejoin the remaining exons (coding regions). |
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Transcription ~ Step 7 |
the mRNA transcript is read to exit the nucleus. |
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Translation ~ Step 8 |
ribosome subunits (large and small) bind to the 5' cap of the mRNA transcript, sandwiching the mRNA between them. Translation commences. The large ribosome subunit contains two sites, the A (acceptor) site and the P (peptide) sites. |
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Translation ~ Step 9 |
the ribosome moves along the mRNA, reading the code in triplets known as codons. Translation does not occur until it reads the triplet AUG, which is the start codon. The start codon corresponds to the amino acid methionine. |
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Translation ~ Step 10 |
when the start codon is in the P site, a tRNA delivers the amino acid methionine. The tRNA recognizes the codon because of the complementary anticodon. |
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Translation ~ Step 11 |
the second codon is now in the A site. The appropriate tRNA delivers the next amino acid in the protein sequence. A peptide bond is formed between methionine and the second amino acid. The ribosome shifts over one codon. The tRNA that delivered methionine is released to obtain another methionine amino acid. The second amino acid tRNA shifts over to the P site. The third amino acid, coded by the third codon, is brought in to the A site by the next tRNA. A peptide bond is formed between the second and third amino acid. |
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Translation ~ Step 12 |
the process of elongation continues until a stop codon is read in the A site. The stop codons are UAG, UGA and UAA. The ribosome stalls. |
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Translation ~ Step 13 |
a protein known as the release factor recognizes that the ribosome has stalled and causes the ribosome subunits to disassemble, releasing the mRNA and newly formed protein. |
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Translation ~ Step 14 |
the protein is folded and modified and then targeted to the area of the cell where it is required. |
