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Chapter 10: Problem 15

List the proteins that unwind DNA during in vivo DNA synthesis. How do they function?

Short Answer

Expert verified
Answer: The main proteins involved in unwinding DNA during in vivo DNA synthesis are helicase, single-strand binding proteins (SSB), and topoisomerase. Helicase unwinds the double-stranded DNA by separating the two strands and creating a replication bubble. Single-strand binding proteins (SSB) bind to the single strands of DNA separated by helicase to prevent them from reannealing and maintain their stability. Topoisomerase relieves the supercoiling generated during the unwinding process by breaking the phosphodiester bonds in the DNA strands, allowing them to rotate, and then resealing the bonds.

Step by step solution

01

List the proteins involved in unwinding DNA

The main proteins involved in unwinding DNA during in vivo DNA synthesis are helicase, single-strand binding proteins (SSB), and topoisomerase.
02

Describe the function of helicase

Helicase plays a crucial role in unwinding the double-stranded DNA. It binds to the DNA at the replication fork and moves along the DNA strand in the 5' to 3' direction, using the energy from ATP hydrolysis. As helicase moves, it separates the two DNA strands, creating a replication bubble.
03

Describe the function of single-strand binding proteins (SSB)

Single-strand binding proteins (SSB) bind to the single strands of DNA that have been separated by helicase. SSBs prevent the separated DNA strands from reannealing, thereby maintaining the stability of the single-stranded DNA and allowing other proteins, such as DNA polymerase, to synthesize a new complementary DNA strand.
04

Describe the function of topoisomerase

Topoisomerase is another essential protein involved in DNA unwinding. As helicase separates the DNA strands, it generates positive supercoiling in the DNA ahead of the replication fork. Topoisomerase acts to relieve this supercoiling by breaking the phosphodiester bonds in one or both DNA strands, allowing the strands to rotate and then resealing the broken bonds. This process reduces the torsional stress on the DNA molecule and helps in the unwinding process.

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Most popular questions from this chapter

Outline the current model for DNA synthesis.

List and describe the function of the ten subunits constituting DNA polymerase III. Distinguish between the holoenzyme and the core enzyme.

Many of the gene products involved in DNA synthesis were initially defined by studying mutant \(E .\) coli strains that could not synthesize DNA. (a) The dnaE gene encodes the \(\alpha\) subunit of DNA polymerase III. What effect is expected from a mutation in this gene? How could the mutant strain be maintained? (b) The \(d n a Q\) gene encodes the \(\varepsilon\) subunit of DNA polymerase. What effect is expected from a mutation in this gene?

Several temperature-sensitive mutant strains of \(E .\) coli display the following characteristics. Predict what enzyme or function is being affected by each mutation. (a) Newly synthesized DNA contains many mismatched base pairs. (b) Okazaki fragments accumulate, and DNA synthesis is never completed. (c) No initiation occurs. (d) Synthesis is very slow. (e) Supercoiled strands remain after replication, which is never completed.

Kornberg showed that nucleotides are added to the 3 '-end of each growing DNA strand. In what way does an exposed \(3^{\prime}\) - OH group participate in strand elongation?
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