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Molecular Biology in a Nutshell (via UCSC Genome Browser) 02-­‐223 Personalized Medicine: Understanding Your Own Genome Fall 2014 DNA • Double-­‐stranded helix made up of the nucleoFdes A, C, G, and T • Sugar in its nucleoFdes is deoxyribose • NucleoFdes form A–T and G–C base pairs across the helix Central Dogma: How the InformaBon in DNA is Expressed Gene DNA (Sequence of A, T, C, G’s) TranscripFon TranslaFon (Sequence of A, U, C, G’s) Protein Nearly universal across all species! (Sequence of amino acids) Genes • In the recent human Encyclopedia of DNA elements (ENCODE) project – ~20,000 protein-­‐coding genes were studies, which covers 2.94% of the genome – Non-­‐protein coding regions of the genome? • >80% of the genome is funcFonal as regulatory sequences, based on the analysis of ENCODE data h_p://www.nature.com/encode/#/threads RNA • RNA is similar to DNA, except that: – it is usually single-­‐stranded – Sequence of A, U, C, G • it has U in place of T, compared to DNA – the sugar in RNA nucleoFdes is ribose instead of deoxyribose – Protein-­‐coding RNA: mRNA Non-­‐protein-­‐coding RNA TranscripBon • TranscripFon begins with binding by RNA polymerase at a promoter region of DNA. • The σ subunit is responsible for promoter recogniFon (in bacteria). • Once iniFaFon has been completed with the synthesis of the first 8–9 nucleoFdes, sigma (σ) dissociates and elongaFon proceeds with the core enzyme. Prokaryote vs Eukaryote Genomes • EukaryoFc mRNAs require processing to produce mature mRNAs. – Introns (intervening sequences) are regions of the iniFal RNA transcript that are not expressed in the amino acid sequence of the protein. – Introns are removed by splicing and the exons (expressed) are joined together in the mature mRNA. • The size of the mature mRNA is usually much smaller than that of the iniFal RNA. • Prokaryote genomes do not have introns Splicing out the Introns TranscripBon in Eukaryotes: Introns and Exons TranscripBon in Eukaryotes: Introns and Exons Transcription Has Been Visualized by
Electron Microscopy Central Dogma Central Dogma RNA derived from complementary bases in DNA In mRNA, triplet codons specify 1 amino acid GeneBc Code for TranslaBon • GeneFc code is degenerate, with many amino acids specified by more than one codon. • Only tryptophan and methionine are encoded by a single codon. • The geneFc code shows order in that chemically similar amino acids oeen share one or two middle bases in the triplets encoding them. IniBator and TerminaBon Codons • TerminaBon codons: UAG, UAA, and UGA do not code for any amino acid. • IniBator codon: AUG is the only codon to encode for methionine. Synonymous and Nonsynonymous MutaBons • Synonymous mutaFons: mutaFons that does not cause the protein code to change • Nonsynonymous mutaFons: mutaFons that cause the protein code to change Summary • Central dogma – TranscripFon of DNA to mRNA – TranslaFon of mRNA to proteins • Introns/Exons in eukaryote genomes