Chapter 17 Notes

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

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Chapter 17 Notes- From Gene to Protein 1. Gene expression is the process by which DNA directs the synthesis of proteins (or in some cases, RNA) 17.1 Genes specify proteins via transcription and translation 1. Evidence from the study of metabolic defects a. Archibald Garrod was the first to suggest that genes dictate phenotypes through enzymes that catalyze specific chemical reactions in the cell. b. He may have been the first person to realize that Mendel’s principles of hereditary apply to humans as well as peas. 2. Nutritional Mutants in Neurospora a. Beadle and Edward Tatum began working with a bread mold and used tests to distinguish among three classes or arginine-requiring mutants. b. They reasoned that each class must be blocked at a different step in this pathway because mutants in that class lacked the enzyme the catalyzes the blocked step. c. They provided strong support for the one gene-one enzyme hypothesis which states that the function of a gene is to dictate the production of a specific enzyme. 3. The Products of Gene Expression: A Developing Story a. Not all proteins are enzymes ex. Keratin and insulin b. One gene-one polypeptide hypothesis : First, many eukaryotic genes can code for a set of closely related polypeptides in a process called alternative splicing. Second, quite a few genes code for RNA molecules that have important functions in cells even though they are never translated into protein. 4. Basic Principles of Transcription and Translation a. Transcription is the synthesis of RNA under the direction of DNA. b. This type of RNA molecule called the messenger RNA (mRNA) because it carries a genetic message from the DNA to the protein-synthesizing machinery of the cell. c. Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA. d. The sites of translation are ribosomes , complex particles that facilitate the orderly linking of amino acids into polypeptide chains. e. Lack of segregation in prokaryotic cells allows translation of an mRNA to begin while its transcription is still in progress. f. The initial RNA transcript from any gene, including those coding for RNA that is not translated into protein, is more generally called a primary transcript. 5. The Genetic Code a. The flow of information from gene to protein is based on a triplet code : The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words. b. For each gene, only one of the two DNA strands is transcribed. This strand is called the template strand because it provides the pattern for the sequence of nucleotides in an RNA transcript. c. The mRNA base triplets are called codons and they are customarily written in the 5’ to 3’. 6.
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This note was uploaded on 02/07/2012 for the course BIO 1711 taught by Professor Burleson during the Spring '11 term at North Texas.

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

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