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5 Cards in this Set
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The enzyme responsible for initiating the unwinding of double-stranded DNA (eliminating supercoiling) by nicking a single strand of the DNA molecule is :
Ο Topoisomerase Ο Gyrase Ο Ligase Ο Helicase |
Topoisomerase
DNA Topoisomerase nicks a single strand of the DNA molecule and this releases the tension holding the two strands together in a supercoiled structure. The enzyme is also known as DNA Gyrase |
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The enzyme that accomplishes the unwinding of the original double stranded DNA molecule, once supercoiling has been eliminated, by breaking the hydrogen bonds that hold the two strands together is :
Ο Helicase Ο Topoisomerase Ο DNA Polymerase II Ο Primase |
Helicase
Helicase seperates the two strands by disrupting the hydrogen bonds that hold the two strands of the DNA molecule together. The resulting unwound and partially opened up helix is called a "replication fork". |
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The enzyme that (during replication) proceeds along one of the strands of a DNA molecule adding deoxy-nucleotide-triphosphates to hydrogen bond with their appropriate complementary dNTP on the other single strand and to form a covalent phosphodiester bond with the previous nucleotide of the same strand is called :
Ο DNA Polymerase III Ο DNA Polymerase II Ο DNA Polymerase I Ο Primase |
DNA Polymerase III
As DNA helicase moves down the DNA molecule and separates the two strands by breaking the bonds between the nitrogenous bases, DNA Polymerase III adds the appropriate complementary bases to the now exposed bases on the single strands. |
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Because DNA polymerase III can only act from 5' to 3', continuous strand growth can be achieved only along one of the template strands (Leading strand) and strand growth along the other strand must occur discontinuously resulting in the production of a series of short sections of new DNA called :
Ο Replicon fragments Ο Okazaki fragments Ο Klenow fragments Ο None of the above |
Okazaki fragments
DNA polymerase III synthesizes new DNA fragments in the 5' to 3' direction along the Lagging strand. These fragments are called Okazaki fragments. |
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The enzyme that replaces the nucleotides of the RNA primer with the appropriate DNA nucleotides is :
Ο DNA Polymerase II Ο RNA Polymerase Ο DNA Ligase Ο DNA Gyrase |
DNA Polymerase II
The correct answer is DNA Polymerase II. DNA polymerase II digests away the RNA primer (on the Lagging strand) and replaces the RNA nucleotides of the primer with the proper DNA nucleotides to fill the gap before DNA Ligase links the strands together. |
