Lecture13-6

Lecture13-6 - Lecture 13 Bacterial Genetics: Mutations,...

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1 Lecture 13 Bacterial Genetics: Mutations, Recombination A. Regulation of Gene Expression B. Bacterial Mutations (Chapter 7 8th ) – Spontaneous mutations – Induced mutations – DNA repair mechanism – Transposable genetic elements – Ames test for mutagens C. Bacterial Recombination (Chapter8 8th ) – Transformation – Conjugation – Transduction A. Regulation of Gene Expression Microorganisms are able to control how much of each building block it makes. Example: When bacterial cell are growing on simple, defined medium , they needs to make all the amino acids. When same cells are growing on complex medium, they can get all the amino acids from the medium. Since biosynthesis of building blocks involve a series of enzymes reactions, the cells either turn on or turn off enzyme synthesis or enzyme activity . Control of protein synthesis • Regulation of enzyme synthesis. • Example: “ Lactose Operon Proposed by Jacob and Monod An example of negative transcription regulation. Control of Protein Synthesis Lactose Operon contains DNA that encodes for: Three enzyme - LacZ ( β -galactosidase), LacY (permease), LacA (transacetylase) And a regulatory protein LacI (Repressor protein) Like Fig. 7.10 Lactose Operon Transcription is controlled by a regulatory protein that binds to DNA. Lac I = Repressor (protein) Operator (DNA site bound by LacI) Off state: (2) No Lactose present for the cell to use. Repressor bound to DNA at operator site. Results: Very little transcription of lacZ , lacY , lacA genes.
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2 Lactose Operon (continued) ON State: (3) Lactose present High lactose results in accumulating allolactose - Inducer (side reaction of β -galactosidase.) allolactose interacts with repressor and alters the repressor’s ability to bind to the operator DNA sequence. Thus: RNA polymerases can interact with promoter DNA. Results: high level of transcription of lacZ , lacY , lacA genes . Fig. 7.10 allolactose B. Mutations and Mutagenesis A mutation is a change in the DNA sequence of a chromosome. note: a mutation involves a change in a nucleotide pair compared to wild type . Can arise spontaneously
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Lecture13-6 - Lecture 13 Bacterial Genetics: Mutations,...

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