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    Presentation1 Presentation1 Presentation Transcript

    • Transcription • Transcription occurs in the cell nucleus where DNA is housed. In transcription DNA is unzipped and the enzyme RNA polymerase runs along the template strand of the DNA. The template strand of DNA can be identified by finding the nucleotide sequence T A C at the 3’ end. This identifies that strand as the template and the other strand, the information strand, will not be used in this transcription. As the RNA polymerase runs along the DNA template strand it will add the complementary RNA nucleotides to the DNA nucleotides. This means that G will be paired with C and A will be paired with U and T paired with A. When the single helix mRNA strand is complete it will separate from the DNA and the DNA will re-zip into the double helix. In eukaryotes, once the mRNA is transcribed it will then be processed. A cap and tail will be added to the ends of the mRNA strand. Then the strand will be spliced. The introns will be removed and the remaining exons will be spliced together. The completed mRNA strand has groups of three nucleotides known as codons. These groups of three will code for a particular amino acid in translation. AUG will code for the start amino acid.
    • Translation • Translation occurs when the mRNA strand moves out of the nucleus and into the cytoplasm. At this point mRNA, rRNA and tRNA all come together. On the large ribosomal unit are two sites- the A site and the P site. These will be the sites of polypeptide synthesis and elongation. The tRNA molecules have an amino acid (the monomer of proteins) attachment site and it also carries an anticodon. The anticodon is the complementary nucleotide sequence to a given codon. The tRNA will pick up the appropriate amino acid in the cytoplasm that is coded for by the mRNA codon that its anticodon matches. In translation the mRNA will run through the rRNA from the 5’ end (with A U G) to the terminating codon at the 3’ end. The first codon, A U G, will start in the A site. There, the tRNA with the appropriate anticodon, U A C, will meet up with the start codon bringing with it the appropriate amino acid, methionine.