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Chapter 17 - From Gene to Protein

Chapter 17 - From Gene to Protein - Chapter 17 Class Notes...

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Chapter 17 Class Notes – From Gene to Protein – Page 1 Max Sauberman AP Biology – Mr. Schilp Chapter 17 From Gene to Protein The Central Dogma: DNA RNA protein synthesis DNA is transcribed to RNA in a process called transcription (the same language). RNA translates the code for protein synthesis through translation, occurring on ribosomes. We need a way to get the DNA out of the nucleus and onto a ribosome in the cytosol, or bound to the rough endoplasmic reticulum. The most important DNA is in the gonads. DNA and RNA Differ: RNA is single-stranded, but it can fold back upon itself to form secondary structure. In RNA, the sugar molecule is ribose rather than deoxyribose. In RNA, the fourth base is uracil rather than thymine. The Flow of Genetic Information: The information content of DNA is in the form of specific sequences of nucleotides. The DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins. Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation. The ribosome is part of the cellular machinery for translation, polypeptide synthesis. Evidence from the study of metabolic defects: In 1909, the British physician Archibald Garrod first suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions. He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme. Linking genes to enzymes required the understanding that cells synthesize and degrade molecules in a series of steps, a metabolic pathway. Nutritional Mutants in Neurospora : Beadle and Tatum exposed Neurospora , bread mold, to X-rays, creating mutants that were unable to survive on minimal medium as a result of their inability to synthesize certain molecules.
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Chapter 17 Class Notes – From Gene to Protein – Page 2 Using crosses, they identified three classes of arginine-deficient mutants, each lacking a different enzyme necessary for synthesizing arginine. They developed a “one gene, one enzyme” hypothesis, stating that each gene dictates the production of a specific enzyme. The Products of Gene Expression: Some proteins aren’t enzymes, so researches later revised the hypothesis to “one gene, one protein”. Many proteins are composed of several polypeptides (like hemoglobin), each of which has its own gene. Therefore, Beadle and Tatum’s hypothesis is now restated as the “one gene, one polypeptide” hypothesis. The Basic Principles of Transcription and Translation: Transcription is the synthesis of RNA under the direction of DNA. Transcription produces mRNA, messenger RNA. Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA. Ribosomes are the sites of translation.
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Chapter 17 - From Gene to Protein - Chapter 17 Class Notes...

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