Bio 201 1st Edition Lecture 34Outline of Last Lecture I. MutationsII. DNA Repair MechanismsA. ProofreadingB. Mismatch RepairC. Excision RepairOutline of Current LectureI. GenesA. George Beadle and Edward TantumII. TranscriptionIII. RNAA. rRNAB. tRNAC. mRNA Current LectureI. Genes- Something inherited that is responsible for an organisms phenotype for a particular character. By 1910’s Thomas Hunt Morgan had shown that genes were locatedon the chromosome. A. George Beadle and Edward Tantum- 1941 experiment, used simple bread mold (nerospora) which is a haploid so mutations will always be expressed, and it is easy to grow. They believed single gene mutants will lack a single enzyme required for synthesis of an amino acid. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-They wanted to know if a single gene corresponds to a single enzyme. They treated mold with x-rays which caused the mold to not grow unless agar contained arginine. (oxotroph- can only grow with presence of certain mutants. ) This eventually showed inactivation of specific enzymes in pathways for arginine synthesis. This confirmed the hypothesis, a single gene single enzyme. X-rays cause heritable alteration of DNA sequence confirmation of DNA as source of genes. II. Transcription- DNA RNA-Messenger RNA is the intermediate between genes (genotype) to protein (phenotype). Translation is RNA protein. Polymerize 5’ to 3’, template is read 3’ to 5’. Catalyzed by RNA polymerase, energy is obtained from hydrolysis of nucleotide triphosphate. RNA is the reverse compliment of DNA template. Nucleotide bases for RNA- A,U,G,C. Does not require a primer because RNA polymerase can initiate de novo. - Transcription in bacteria- sigma factor binds to core promoter, 10 & 35 bases upstream of transcription start site (-10 & -35 relative to txn start site). RNA polymerase initiates polymerization at transcription start site (base 0). Promoters for different genes have slightly different sequences and are therefore recognized by different sigma factors. Different factors are activated by different signals transcription of genes only when needed. -Transcription in eukaryotes- Specific transcription factors bind to enhancers in DNA. General transcription factor TFIID binds to core promoter, located ~25 bases upstream of transcription start sire. TFIID and its partners recruit RNA polymerase and other essential proteinstranscription. III. RNA-3 types: mRNA- messenger RNA, protein coding intermediate. tRNA- transfer RNA, brings amino acids to growing polypeptides. rRNA- Ribosomal RNA- catalyzes polymerization of polypeptides. A. rRNA- 60% w/w of ribosome. rRNA is a ribozyme that catalyzes peptide bond formation, transcribed in the nucleolus. 3D structure is achieved through extensive intramolecular base pairing, mutations are extremely rare. Extremely high degree of conservation allows rRNA sequences to be used to classify distant organisims, in humans, an average of nearly 100 copies each of different genes. B. tRNA- Carrier for amino acid during polypeptide synthesis. Different tRNA for each amino acid. Extensive base-pairing maintains 3D structure. Sequence highly conservedthroughout evolution, present in all species. Highly conserved, approximately 50 differenttRNA genes classified based on anticodon sequence. C. mRNA- Used for eukaryotic transcription. Encodes protein, highly regulated. Must be exported into cytoplasm for translation, and processed prior to
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