Genes and How They Work - TheNatureofGenes...

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The Nature of Genes - Early ideas to explain how genes work came from studying human diseases - Archibald Garrod — 1902 - Recognized that alkaptonuria is inherited via a recessive allele - Proposed that patients with the disease lacked a particular enzyme - These ideas connected genes to enzymes Beadle and Tatum — 1941 - Deliberately set out to create mutations in chromosomes and verify that they behaved  in a Mendelian fashion in crosses - Studied Neurospora crassa - Used X-rays to damage DNA - Looked for nutritional mutations - Had to have minimal media supplemented to grow - Looked for fungal cells lacking specific enzymes - The enzymes were required for the biochemical pathway producing the amino  acid arginine - They identified mutants deficient in each enzyme of the pathway - One-gene/one-enzyme hypothesis has been modified to one-gene/one-polypeptide  hypothesis Central Dogma - First described by Francis Crick - Information only flows from DNA —> RNA —> protein - Transcription = DNA —> RNA - Translation = RNA —> protein - Retroviruses violate this order using reverse transcriptase to convert their RNA  genome into DNA - Transcription - DNA-directed synthesis of RNA - Only template strand of DNA used - U in DNA replaced by T in RNA - mRNA used to direct synthesis of polypeptides - Translation  - Synthesis of polypeptides - Takes place at ribosome - Requires several kinds of RNA RNA - All synthesized from DNA template by transcription - Messenger RNA (mRNA) - Ribosomal RNA (rRNA) - Transfer RNA (tRNA)
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- Small nuclear RNA (snRA) - Signal recognition particle RNA (SRP RNA) - Micro-RNA (miRNA) Genetic Code - Francis Crick and Sydney Brenner determined how the order of nucleotides in DNA  encoded amino acid order - Codon —> block of 3 DNA nucleotides corresponding to an amino acid - Introduced single nucleotide insertions or deletions and looked for mutations - Frameshift mutations - Indicates importance of reading frame Spaced & Unspaced Codons - Spaced - Codon sequence in a gene punctuated - Unspaced - Codons adjacent to each other - Marshall Nuremberg identified the codons that specify each amino acid - Stop codons
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