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12 Cards in this Set
- Front
- Back
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What is the main difference between class I and class II topoisomerases?
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Class I: cuts only one strand of DNA, no ATP required
Class II: cuts both strands of the DNA, uses ATP |
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What is the function of Class IA topoisomerases?
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-relaxes ONLY negatively supercoiled DNA by cutting one strand and allowing it to unwind
-can catenate 2 strands ssDNA -uses tyr residue to hang on to 5' P of nicked strand while it passes the other strand through. |
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What is the function of Class IB topoisomerases?
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-relaxes + OR - supercoils by breaking one strand and allowing it to unwind one turn.
-covalent intermediate using Tyr residue as in Class IA. |
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What is the function of Topoisomerase II?
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cuts one strand of dsDNA, passes other strand through, reconnects cut strand.
changes linking number by +/- 2. ATP required for release of second strand --> ensures unidirectionality of process. |
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What is special about DNA Gyrase?
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-only prokaryotic
-only known enzyme that can MAKE negative supercoils in DNA -can recognize and selectively coil up ssDNA eukaryotic enzyme can only relax DNA. |
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What are the characteristics of histones?
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~100 angstroms in diameter
-protein "spools" around which DNA wraps. -1.65 wraps of DNA per histone -histone + charged to attract - DNA (backbone is negative). -can be acetylated to control DNA binding. |
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What is the purpose of Histone H1?
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help link nucleosomes (histone + DNA wound around it) together and further condense the chromosome.
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What are the differences between A, B, and Z-DNA?
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A DNA: flatter, wider double helix, axial hole, base pair axes tilted more. ~ribbon wound around a cyndrilical hole.
B-DNA: most common, base pair axes almost perpendicular to helix axis, lacks central cavity of A-DNA Z-DNA: left handed helix, flat major grooves, thinner helix diameter, tighter, steeper twist. usually polyA/G/C/T in high salt conc. |
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Which direction produces "negative twist" and "negative supercoils?"
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left-handed twist
produces right-handed supercoils/writhe. |
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Which direction produces "positive twist" and "positive supercoils?"
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right-handed twist (as in normal duplex DNA)
produces left-handed supercoils/writhe. |
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Which groups are in the major groove in the TA base pair? Which are in the minor groove?
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Major: adenine amino grp, thymine C4 carbonyl
Minor: thymine's C2 carbonyl |
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Which groups are in the major groove in the GC base pair? Which are in the minor groove?
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Major: guanine's carbonyl, cytosine's amino group
Minor: guanine's amino group, cytosine's carbonyl |
