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30 Cards in this Set
- Front
- Back
The Organization of DNA in Prokaryotic Cells: Archaea and Bacteria |
- DNA is a circular double helix - further twisting results in supercoiled DNA - supercoiling is required so that the chromosome "fits" into the cell - in bacteria, the RNA is associated with protein HU |
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DNA gyrase |
A topoisomerase creates supercoils to compact bacterial chromosome |
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Protein HU |
Helps organize DNA into a packed chromatin linked structure |
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DNA Replication in Prokaryotes |
- Replication begins at a "single" site known as the origin of replication - multienzyme replication complex binds to origin - separated DNA strands serve as templates for DNA polymerase - 2 characteristic replication forks are formed, which proceed in opposite directions around the chromosome - 2 copies of the total genetic information produced during replication are each composed of one parental strand and one newly synthesized strand of DNA (semi conservation replication) |
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Semi Conservation Replication |
2 copies of the total genetic information produced during replication are each composed of one parental strand and one newly synthesized strand of DNA |
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Origin of Replication |
"Single" site where replication starts |
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Helicases |
Seperate and unwind DNA strands |
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Topoisomerases |
Relieve tension generated by rapid unwinding (transiently break one or two strands without altering nucleotide sequence) |
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Single-Stranded DNA binding proteins (SSBs) |
Keeps the strands apart once separated
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Chromosome Replication and Partitioning (3 Elements) |
In most prokaryotes: Origin of replication: site at which replication begins Terminus: site at which replication is terminated Bidirectional from a single origin of replication |
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DNA Replication in Rapidly Growing Cells: Cell Cycle |
Cell cycle completed in 20 minutes 40 minutes for DNA replication, 20 minutes for septum formation and cytokinesis - Second, third, or fourth round of replication can begin before first round of replication is completed - when bacteria are growing rapidly, they initiate new rounds of DNA replication before an existing round of replication has finished (daughter cells inherit DNA that has already initiated its own replication) |
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Cell cycle completed in __ minutes: ___ minutes for DNA replication, ___ minutes for septum formation and cytokinesis. How is this possible? |
20, 40,20 Why? Second, third, or fourth round of replication can begin before first round of replication is completed |
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DNA Polymerases |
Catalyze synthesis of complementary strand of DNA (DNA polymerase III plays major role in replication in prokaryotes) - require template, primer, dNTPs |
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DNA synthesis is in ___ and nucleotides are linked by ___ bonds |
5' to 3' direction; phosphodiester |
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DNA Polymerases require __,__, and __. |
- Template: directs synthesis of complementary strand - Primer: RNA strand to provide a 3' hydroxyl group to which nucleotides can be added; made by primase - dNTPs (dATP, dTTP, dCTP, dGTP): deoxynucleoside triphosphates |
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Leading Strand |
Synthesized continuously at its 3' end as the DNA unwinds as DNA polymerase enzymes must synthesize DNA in the 5' to 3' direction |
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Lagging Strand |
- cannot be extended in the same direction because there is no free 3' OH to which a nucleotide can be added - synthesized discontinuously in the 5' to 3' direction as a series of fragments |
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Primase |
Adds many RNA primers along the single-stranded lagging strand |
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DNA Polymerase III |
Extends primers made by primase with DNA to form short fragments |
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Helicase |
Unwind DNA |
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Topoisomerases |
Relieve tension generated by rapid unwinding |
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DNA polymerase |
Catalyzed DNA synthesis |
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Okazaki Fragments |
Lagging strand is synthesized in short fragments; a new primer is needed for the synthesis of each Okazaki fragment |
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Completion of Lagging Strand Synthesis |
- DNA polymerase I removed the RNA primer and fills gap with DNA but a nick remains - Okazaki fragments are joined by the enzyme DNA ligase; forms phosphodiester bond between 3' hydroxyl of the growing strand and the 5' phosphate of an Okazaki fragment |
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DNA Polymerase III |
- does proofreading - checks each newly incorporated base to see that it forms stable hydrogen bonds |
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DNA Polymerase III |
- mismatched base removed from 3' end of growing strand by exonuclease activity of the DNA polymerase III enzyme; adds proper base after |
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Termination site (ter in E.coli) |
Where replication stops when replisome reaches here |
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Tus Proteins |
Binds to ter sites and halts progression of the forks |
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Catenanes |
Form when 2 circular daughter chromosomes are interlocked following replication of the DNA and do not separate |
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____ solves this problem of not seperation by temporarily breaking the DNA molecules so the strands can seperate |
Topisimerases |