How Nucleotides Are Added in DNA Replication

Why is DNA uncoiled before replication? DNA replication requires that the complementary strands separate. A new complementary strand is then synthesized onto each of the existing strands. The end result is two double stranded molecules. If the original strand did not uncoil then, even if synthesis was possible, the two new molecules would be hopelessly entangled. In DNA synthesis events occur in the following order: a portion of the original molecule uncoils and the two strands separate in that region. Then DNA polymerase synthesizes complementary strands. Finally the two strands for each new molecule attach and coil up.

View the animation below, then complete the quiz to test your knowledge of the concept.


1	Arrange the following proteins in the proper order in which they participate in DNA replication. 1 = Primase 2 = Helicase 3 = Single-strand binding proteins 4 = DNA polymerase I

		A)	1, 2, 3, 4
		B)	1, 3, 2, 4
		C)	2, 3, 1, 4
		D)	2, 3, 4, 1
		E)	2, 4, 3, 1

2	Which of the following is required to replicate the lagging strand of DNA?

		A)	Okazaki fragments
		B)	primase
		C)	DNA ligase
		D)	A and B
		E)	A, B and C

3	RNA primers are removed by the action of the enzyme

		A)	DNA pol III.
		B)	DNA pol I.
		C)	primase.
		D)	helicase.
		E)	phophodiesterase.

4	DNA pol III can initiate DNA synthesis.

		A)	True
		B)	False

5	To allow simultaneous replication of the leading and lagging strands by dimeric DNA pol III, the DNA of the leading strand has to be folded.

		A)	True
		B)	False

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