fifth reading f 17 & 18.1-18.5

fifth reading f 17 & 18.1-18.5 - Emily Lin...

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Emily Lin 2/22/2011 Chapter 17 serves to explain gene expression, when a protein or other gene product is synthesized and active in the cell, in bacteria, which allows them the ability to cope with environmental chances and allows them practical significance. Biologists predict that transcription and translation of individual genes in bacteria are triggered by specific signals from the environment. The chapter looks at the genes in metabolizing lactose in this case. Gene expression can be controlled at any step between the synthesis of RNA and the activation of the final gene product. Bacterial cells use resources efficiently by 1. Avoid making the mRNAs for particular enzymes (transcriptional control 2. Preventing a way for the mRNA from getting translated into protein (translational control), and 3. Activating inactive proteins with chemical modification (post-translational control). Transcriptional control is slow, but efficient in resource use. Post-translational is fast but energetically expensive. Some genes, are transcribed all the time, or constitutively. Variation in gene expression allows cells to respond to changes in the environment. Inducers stimulate expression of specific genes and molecules. Genetic screens include generating a large number of individuals with mutations at random locations in their genomes and screening them to find individuals with defects in the process or biochemical pathway in question. Positive and negative control also comes into play by triggering and shutting down transcription respectively. In lactose, it induces transcription by removing negative control by the repressor. Operons are sets of coordinately regulated bacterial genes that are transcribed together into one mRNA. Catabolite repression is a form of end-product
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fifth reading f 17 & 18.1-18.5 - Emily Lin...

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