Ch8 Micro - Ch8

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Ch8 -constitutive v. inducible genes: what is the significance of this? relevance  to infection? Some proteins are constitutive: made all the time Others are inducible: made only when needed (60-80%) ex. Flagellin for flagella, virulence factors: toxins, hemolysins (lyse RBC) A constitutive gene is a gene that is transcribed continually at a fixed rate. These genes encode for enzymes that the cell needs in fairly large amounts for it’s major life processes. Inducible gene is a gene whose expression is responsive to environmental change or dependent on the position of the cell cycle. These genes are required for lactose metabolism in E.coli and are a well known inducible system. Cells save energy by making only those proteins needed at a particular time. The inducible system prevents the cell from wasting precious energy for unnecessary enzymes. It is only activated when a certain inducer is present. Relevance to infection? -bacterial genome makeup, general size, bidirectional replication Bacteria have a circular chromosome consisting of a single circular molecule of DNA with associated proteins. Chromosome is looped and folded and attached at one or several points of the plasma membrane. Bacterial Chromosome -The chromosome is a small circle: it is coiled, and then super coiled so as to take up <10% of cell’s volume -E.coli chromosome is 4x10^6 bp (base pairs). The chromosome is attached to the membrane; enables one new copy to be appropriately distributed to each new cell during division Replication -Replication is bidirectional -Replication proceeds away from the origin in both directions, cutting the time required to duplicate the chromosome in half (down to 20). It is Semi-Conservative. -Enzymes involved in semi-conservative replication and the process itself
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Enzymes involved in semi-conservative replication involve topoismoerase, helicase, ligase, and primase. 1. Synthesis on the leading strand is continuous 2. Primase assembles a short RNA primer of ~10 nucleotides 3. DNA pol III extends primer with DNA nucleotide along the rest of chromosome 4. DNA pol I has an editing function. Beta replicates RNA with DNA 5. Ligase seals any nicks in the DNA backbone Sythesis on lagging strand is discontinuous These enzymes all want to synthesize in a 5’ 3’ direction on the lagging strand, synthesis wants to travel in wrong direction 1. primase assemble a short RNA primer about 10 nt long 2. Pol III adds in DNA nt; it can synthesize ~1000 nt, then stop “okazaki fragments” 3. The synthesizing enzymes leap up the fork, to synthesize DNA until blocked by the first primer Primase ligase Pol III Pol I -The fidelity of replication is impressive. DNA pol enzymes have proof reading and editing capabilities. Wrongly inserted nt tend to be detected, fixed.
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This note was uploaded on 05/03/2011 for the course BIOL 300 taught by Professor Toeph during the Spring '11 term at Brescia.

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Ch8 Micro - Ch8

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