Textbook Question
Write a short essay that distinguishes between the terms replication and synthesis, as applied to DNA. Which of the two is most closely allied with the field of biochemistry?
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8. DNA Replication
Overview of DNA Replication
1:34 minutesProblem 6
Textbook Question
What are the requirements for in vitro synthesis of DNA under the direction of DNA polymerase I?
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Understand the role of DNA polymerase I: DNA polymerase I is an enzyme that synthesizes DNA by adding nucleotides to a pre-existing strand, using a template strand as a guide.
Identify the need for a DNA template: DNA polymerase I requires a single-stranded DNA template to direct the synthesis of a complementary strand. This template provides the sequence information for the new DNA strand.
Recognize the importance of a primer: DNA polymerase I cannot initiate DNA synthesis on its own. It requires a short, pre-existing strand of DNA or RNA (called a primer) with a free 3'-hydroxyl (-OH) group to begin adding nucleotides.
Include the four deoxynucleoside triphosphates (dNTPs): The enzyme requires the building blocks of DNA—dATP, dTTP, dCTP, and dGTP—to synthesize the new strand. These molecules provide both the nucleotides and the energy for the polymerization reaction.
Ensure the presence of magnesium ions (Mg²⁺): Magnesium ions act as cofactors for DNA polymerase I, stabilizing the enzyme and facilitating the catalytic activity during DNA synthesis.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
DNA Polymerase I Function
DNA Polymerase I is an enzyme that plays a crucial role in DNA replication and repair. It synthesizes new DNA strands by adding nucleotides complementary to the template strand. This enzyme also possesses exonuclease activity, allowing it to remove RNA primers and replace them with DNA, ensuring the integrity of the newly synthesized DNA.
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Nucleotide Requirements
For in vitro DNA synthesis, a supply of deoxynucleotide triphosphates (dNTPs) is essential. These building blocks—adenine (dATP), cytosine (dCTP), guanine (dGTP), and thymine (dTTP)—are required for the polymerase to add nucleotides to the growing DNA strand. The correct concentration and balance of these dNTPs are critical for efficient and accurate DNA synthesis.
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Template Strand
A template strand is necessary for DNA polymerase to synthesize a new DNA strand. The enzyme reads the sequence of the template strand and incorporates complementary nucleotides to create a new strand. The presence of a suitable template ensures that the synthesized DNA is an accurate copy of the original sequence, which is vital for genetic fidelity.
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