Zoology101: Animal Biology Last Lecture Outline Lecture 11 1. Finish up of last lecture2. Replicating ends of Linear Chromosome3. Repairing mistakes in DNA synthesis4. Packing a eukaryotic chromosomeCurrent Lecture 1. Transcription2. Eukaryotic Initiation 3. TranslationTranscription• tRNA gene → tRNA (transfer)• rRNA gene → rRNA (ribosomal)• snRNA gene → snRNA (small nuclear RNA)• Protein-coding genes → mRNA (messenger RNA) • The synthesis of RNA using a DNA template (Happens in nucleus, needs DNA template → Eukaryotic) • Features of a gene: ◦ Start site ◦ Transcription unit- Codes for mRNA ◦ Terminator ◦ Promoter : on off switch signals that a gene is next to it ◦ Requires a RNA polymerase • Initiation: RNA polymerase binds to promoter and unwinds DNA; makes transcription bubble ◦ unlike DNA, only uses 1 strand ◦ Adds nucleotides complementary to template stand ◦ RNA builds in a 5 prime to 3 prime direction (Same as DNA)◦ No need for helicase ◦ No need for a primer • Elongation: RNA transcript opens up transcription bubble adds nucleotides • Termination: RNA polymerase recognizes termination signal and stops,RNA transcript releases “downstream” Eukaryotic Initiation • Complicated • TATA box (eukaryotic promoter- 25 base pairs before transcription starts.. “Downstream”.. indicates where RNA poly has to bind • Transcription factor bind to TATA so RNA poly can come along• Transcription initiation complex: transcription factor and RNA poly• Eukaryotes modify mRNA after transcription ◦ Pre-mRNA matures by-◦ 1. adding a cap for stability of RNA and for positioning ribosomes▪ adding an A-tail to stabilize RNA and have a long tail for a longer life• Exported from nucleus • Poly A binding proteins (Nuclear export signal)◦ 2. Removes introns= intervening sequence▪ RNA splicing: introns are cut out and exons (expressed genes) are spliced together ▪ RNA transcript (pre-mRNA), small nuclear RNA: found in nucleus ▪ Small nuclear ribonuclearproteins (snurps) → Protein and an RNA ▪ snRNA base pairs with specific nucleotide in intron → spliceosome comes along (recognizes introns, cuts pre-mRNA) → splits into sliceosome components, mature DNA and cut out intron • Why introns?◦ Splicing necessary for movement of RNA from nucleus to cytosol ◦ alternative RNA splicing- one gene can encode more than 1 polypeptide; have 21,000 genes but 100,000 proteins Translation• Using information in mRNA to make polypeptide◦ DNA (info storage) → mRNA (info transfer)▪ Untranslated regions are at 3 prime and 5 prime ends; helps bind ribosomes ▪ Translation starts in codon AUG• The genetic code: code connecting codon to amino acid ◦ not ambiguous: if you know which codon, you know what your amino acid is in the polypeptide ◦ redundant: an amino acid can be specified by more than one codon◦ universal: can be used for different things....i.e. The glowing jelly fish gene cat◦ not overlapping: specific reading from, separate words • Transfer RNA (tRNA): connection between specific reading fram ◦ Amino acid attachment site (tRNA can bind here)◦ Other end: anticodon will bind with complementary codon in mRNA ◦ Look at complementary codon to figure out amino acid▪ tRNA connects to amino acid → aminoacyl tRNA synthetases- connects amino acids and tRNA• Charged tRNA- tRNA attached to an amino acid • Ribosomes are the workbench◦ Are ribonucleoprotein complexes ◦ large and small subunits (EUK and PROK are different)◦ Move out of nucleus into cytoplasm ◦ subunits join when translation
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