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Lecture 4

Lecture 4 - Gene and Genome Structure

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Biology 2581B
Jim Karagiannis

LECTURE 3: GENEAND GENOME STRUCTURE Key Concepts 1. Central Dogma of Molecular Biology and Genetics (circa 2012) 2. Anatomy of a gene 3. Anatomy of a genome DNA: Information Storage and Retrieval • DNAstores the biological information to create a diverse range of protei▯cell types▯ tissues▯ organisms • Advantages: o Ease of storage (large quantity of data) o Can be copied reliably DNAStores Information “Digitally” • Analogous to storing electronic data such as music: o Digitized information on your computer hard driv ▯mp3 player  ▯ sound waves  ▯music Central Dogma of Molecular Biology and Genetics • DNA  ▯ RNA  ▯Protein • DNAis the information source, can replicate it and store it • Can also be transcribed as an RNA molecule, which is shelled out of the cell to code for proteins • The central dogma is generally not true, as there are RNAs that are not transformed into proteins – but stays true for the most part The Flow of Information in Biological Systems • Read in two orders, one strand is 5’ to 3’ directionality • Complementary strand is 5’ to 3’ in the opposite direction • 5’ to 3’ is what codes for the RNAstrand – which is complementary to 3’ to 5’ • Rather than looking at a single gene or species, we can look at an entire genome at multiple levels in a given tissue at a given time (polymorphisms, exons, transcriptome, etc.) • Generally what we are interested in is the phenotype What is a Gene? • The basic unit of biological information • Aspecific segment of DNAat a specific location in the genome (on a region of a chromosome) that serves as a unit of function – encodes RNAor protein Anatomy of a Eukaryotic Gene • Basic transcriptional machinery – GC, CAAT, TATAbox • 5’ UTR – (untranslated region) – not translated, where transcription starts • RNApolymerase starts building nucleotides here • Within exon 1 (or exon 2 or 3), the start codon is found • Proteins stop at 3’ UTR but RNA translation continues • Splice donor site – donates information (GTAG) – when spliced out, these two regions come together • Once mRNAtranscript has been transcribed, mature RNAhas to be translated • mRNA– single-stranded molecules, very unstable • PolyAtail – helps our cells recognize mRNA Genes between Species • Genes between species vary considerably • Structure of collagen gene in C. elegans is very simple • Comparatively, the dystrophin gene in H. sapiens is much more complex • Intronic information is taken out, and some exons are also taken out due to splicing • In any given tissue, where dystrophin is expressed, you can have some or very few exons resulting in a slightly different protein • Also has multiple promoters which are specific to various tissue types • Different splicing, various promoters – essentially form the same protein, which is why they all have the same function Sequence to Function • Open reading frame (ORF) – in-frame sequence of DNAthat starts with start codon (ATG) and ends with any of the three termination (stop) codons (TAA, TAG, TGA) • Coding sequence (CDS) – region of DNAthat is translated to form proteins The Genetic Code • 21 amino acids, 64 possible codons • Considerable amount of redundancy • Part of this is because of evolu
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