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Chapter 11: Problem 18

What is an Okazaki fragment? In which strand of replicating DNA are Okazaki fragments found? Based on the properties of DNA polymerase, why is it necessary to make these fragments?

Short Answer

Expert verified
Okazaki fragments are short DNA sequences formed on the lagging strand during DNA replication. They are necessary because DNA polymerase, the enzyme that catalyzes DNA synthesis, can only add nucleotides in the 5' to 3' direction, and thus, while the leading strand can be synthesized continuously, the lagging strand has to be synthesized discontinuously in the form of Okazaki fragments.

Step by step solution

01

Defining Okazaki Fragments

Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes), which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication.
02

Locating Okazaki Fragments in DNA strand

Okazaki fragments are found in the lagging strand of the replicating DNA. So during DNA replication, one strand (leading strand) is replicated continuously in the 3' to 5' direction, while the other strand, known as the lagging strand, is replicated discontinuously in fragments known as Okazaki fragments, in the 5' to 3' direction.
03

Linking Okazaki fragments to the Properties of DNA Polymerase

The reason why DNA polymerase makes these fragments lies in its properties. DNA polymerase can only add nucleotides in the 5' to 3' direction. On the leading strand, replication can proceed continuously, but on the lagging strand, replication is discontinuous, with DNA synthesized in short stretches (Okazaki fragments) moving away from the replication fork. Thus, these fragments are necessary due to the unidirectional nature of DNA polymerase, making it unable to synthesize both strands continuously.

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Most popular questions from this chapter

Explain the proofreading function of DNA polymerase.

As discussed in Chapter 18, some viruses contain RNA as their genetic material. Certain RNA viruses can exist as a provirus in which the viral genetic material has been inserted into the chromosomal DNA of the host cell. For this to happen, the viral RNA must be copied into a strand of DNA. An enzyme called reverse transcriptase, encoded by the viral genome, copies the viral RNA into a complementary strand of DNA. The strand of DNA is then used as a template to make a double-stranded DNA molecule. This doublestranded DNA molecule is then inserted into the chromosomal DNA, where it may exist as a provirus for a long period of time. A. How is the function of reverse transcriptase similar to the function of telomerase? B. Unlike DNA polymerase, reverse transcriptase does not have a proofreading function. How might this affect the proliferation of the virus?

Describe the three important functions of DnaA protein.

Which of the following statements is not true? Explain why. A. A DNA strand can serve as a template strand on many occasions. B. Following semiconservative DNA replication, one strand is a newly made daughter strand and the other strand is a parental strand. C. A DNA double helix may contain two strands of DNA that were made at the same time. D. A DNA double helix obeys the AT/GC rule. E. A DNA double helix could contain one strand that is 10 generations older than its complementary strand.

C1. What key structural features of the DNA molecule underlie its ability to be faithfully replicated?
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