Lecture 9 to12 Central Dogma

Lecture 9 to12 Central Dogma - Lecture 9-13 The Central...

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Unformatted text preview: Lecture 9-13 The Central Dogma Transcription and translation What you should know after the lecture: Molecular aspects of transcription and translation Gene Theory: In 1953, James Watson and Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had (then) recently been deduced to be the physical carrier of inheritance (gene). The discovery that genes are made of DNA left an unanswered question: How does the sequence of a strand of DNA correspond to the amino acid sequence of a protein ? Crick linked DNA to proteins, an idea since referred to as the central dogma: Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" of proteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins). According to the central dogma, information flow is from DNA (human genome contains some 26,000 genes) to RNA (selectively transcribed from DNA) via the process of transcription, and thence to protein via translation . Transcription is the making of RNA molecule off an DNA template and translation is the construction of a protein from an RNA molecule. Exception to central dogma: Some viruses contain RNA genomes and encode an enzyme-reverse transcriptase-which can make DNA copies base on the RNA blueprint. (These viruses are just like people who keep the copy of the recipe book. When they go into the library, they put back these special recipes in the book and let you copy it and bring it back to your kitchen) Transcription Requirements Double-stranded DNA template strand (containing promoter, coding region and termination signal) RNA polymerase (Enzyme that catalyze the synthesis of RNA) GTP or ATP as the starting nucleotide NTPs Mg 2+ How can the enzyme RNA polymerase recognize the correct sequence to be transcribed? The enzyme cannot start randomly on DNA strand as this might generate the incorrect RNA sequences. Answer: based on the information (specific sequence) on the DNA: promoter (a specific DNA sequence that the RNA polymerase recognized and starts the transcription) DNA template strand: Not all of the template DNA code for protein sequence Key features of prokaryotic gene structure and regulation: Promoter region (transcriptional regulation) Positive control: Something (protein/protein complex) must bind to promoter, otherwise gene is off. Untranslated region (UTR) -- 5' and 3' regions sequences in these regions can still regulate gene expression. For example, the stability (half-life) of the mRNA. Ribsome binding sequence (RBS)-for translation. Protein coding sequence-Open reading frame Termination signal sequence-for termination of transcription RNA polymerase used for all genes, but with different co-factors (sigma factors) RNA synthesis in E.Coli (Prokaryotes) 1. Initiation: search DNA to find promoter sites unwind a region of DNA to form replication bubble...
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Lecture 9 to12 Central Dogma - Lecture 9-13 The Central...

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