Textbook Question
How do covalent bonds differ from hydrogen bonds? Define base complementarity.
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7. DNA and Chromosome Structure
DNA Structure
2:07 minutesProblem 18
Textbook Question
List the order in which the following proteins and enzymes are active in E. coli DNA replication: DNA pol I, SSB, ligase, helicase, DNA pol III, and primase.
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Understand the process of DNA replication in E. coli, which involves unwinding the DNA, stabilizing the strands, synthesizing primers, elongating the new strands, and sealing the gaps.
The first enzyme to act is helicase, which unwinds the DNA double helix at the replication fork by breaking hydrogen bonds between complementary bases.
Next, single-strand binding proteins (SSB) bind to the separated DNA strands to prevent them from reannealing and to protect them from degradation.
Primase synthesizes short RNA primers on the lagging strand (and occasionally on the leading strand) to provide a starting point for DNA polymerase to begin synthesis.
DNA polymerase III (DNA pol III) extends the RNA primers by adding nucleotides in the 5' to 3' direction, synthesizing the bulk of the new DNA strand. DNA polymerase I (DNA pol I) later replaces the RNA primers with DNA, and DNA ligase seals the nicks in the sugar-phosphate backbone to complete the replication process.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DNA Replication Process
DNA replication in E. coli is a highly coordinated process involving multiple enzymes and proteins that work in a specific order to ensure accurate duplication of the genetic material. The process begins at the origin of replication and proceeds bidirectionally, requiring the unwinding of the DNA double helix and the synthesis of new strands complementary to the original template.
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Steps to DNA Replication
Role of Key Enzymes
Each enzyme involved in DNA replication has a distinct role. Helicase unwinds the DNA double helix, single-strand binding proteins (SSB) stabilize the unwound strands, primase synthesizes RNA primers, DNA polymerase III extends the new DNA strand, DNA polymerase I replaces RNA primers with DNA, and ligase seals the gaps between Okazaki fragments on the lagging strand.
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Order of Enzyme Activity
The order of enzyme activity during E. coli DNA replication is crucial for the process's efficiency and accuracy. It typically follows this sequence: helicase, SSB, primase, DNA pol III, DNA pol I, and finally ligase. Understanding this sequence helps clarify how each enzyme contributes to the overall replication process and ensures that the DNA is copied correctly.
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