Questions and Answers
What is the function of single-stranded binding proteins during DNA replication?
How does DNA polymerase III primarily contribute to DNA replication?
Which enzyme is responsible for relieving the tension that develops as the DNA helix unwinds?
What describes the direction of DNA replication in terms of nucleotide addition?
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What role does the sliding clamp play in DNA polymerase III?
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Which of the following accurately describes the synthesis of the lagging strand?
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Which component of the replisome helps to provide the initial hydroxyl group required for DNA synthesis?
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What is the primary role of DNA polymerases II, IV, and V?
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What distinguishes eukaryotic DNA replication from prokaryotic DNA replication regarding the origin of replication?
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During DNA replication in eukaryotes, what happens to histones?
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Which statement correctly describes the structure of nucleosomes?
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What is the role of DNA polymerase alpha in eukaryotic DNA synthesis?
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Which of the following accurately describes Okazaki fragments in eukaryotes?
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What is the primary function of telomerase in relation to telomeres?
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What is a significant difference in the termination process of eukaryotic and prokaryotic DNA replication?
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What requirement is essential for both prokaryotic and eukaryotic DNA synthesis?
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Which component of telomerase serves as a template for DNA synthesis?
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During homologous recombination, what is the role of endonucleases?
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How does the rate of DNA synthesis compare between prokaryotes and eukaryotes?
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What process follows the strand displacement in homologous recombination to extend the heteroduplex DNA?
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Which protein is considered crucial for the process of homologous recombination?
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What is the outcome of DNA ligation in the recombination process?
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Why do most somatic cells experience telomere shortening over time?
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In the context of DNA synthesis, what does the lagging strand require to successfully elongate?
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Study Notes
DNA Polymerase Functions
- DNA polymerase I removes RNA primers and fills gaps using 5’-3’ exonuclease activity, allowing for proofreading.
- DNA polymerases II, IV, and V are involved in repairing damage caused by external forces like UV light.
DNA Polymerase III Holoenzyme
- Composed of two core enzymes, a sliding clamp loader, and a sliding clamp to enhance processivity.
- Major enzyme complex for prokaryotic DNA replication, adding nucleotides to RNA primers and synthesizing leading and lagging DNA strands.
- Enzymes and proteins at the replication fork form a structure known as the replisome.
Mechanism of DNA Synthesis
- DNA replication is bidirectional but occurs biochemically in one direction (5' to 3').
- Single-stranded binding proteins prevent reformation of hydrogen bonds.
- Gyrase alleviates tension from unwinding DNA.
- Primase provides RNA fragments necessary for DNA polymerase III to start polymerization.
- Leading strand synthesis is continuous; lagging strand synthesis involves Okazaki fragments and is discontinuous.
- Lagging strand gaps are filled and ligated post-replication.
Eukaryotic DNA Synthesis
- Requires deoxyribonucleoside triphosphates (dNTPs), template, and primer.
- More complex due to increased DNA volume and linear chromosomes, with DNA dissociating from histones before replication.
- Synthesis of DNA and production of histones occurs simultaneously, doubling histone count during replication.
Comparison: Prokaryotic vs. Eukaryotic Replication
- Prokaryotes have a single origin of replication; eukaryotes have multiple.
- Prokaryotes expand from a single replication loop; eukaryotes have multiple loops for increased efficiency.
- Prokaryotic replication ends at a single termination site; eukaryotic involves merging two replication forks and telomere replication.
Eukaryotic DNA Polymerases
- Pol α initiates and synthesizes the RNA primer, adds 10-20 nucleotides, and is replaced by Pol δ and Pol ε for further synthesis.
- Pol δ synthesizes the lagging strand; Pol ε synthesizes the leading strand.
- Pol γ is responsible for mitochondrial DNA replication.
Telomeres and Aging
- Linear chromosome ends, known as telomeres, shorten with repeated cell divisions in somatic cells lacking telomerase.
- Telomeres contain repetitive G-rich sequences and do not code for genes.
- TERT gene encodes telomerase reverse transcriptase crucial for telomere maintenance.
- TERC component serves as a guide for enzyme attachment and as a template for DNA synthesis.
DNA Recombination
- Occurs through reciprocal exchange of homologous chromosomes involving several steps:
- Endonuclease nicks DNA strands.
- Strand displacement pairs loose ends with complementary sequences.
- Ligation forms hybrid heteroduplex DNA.
- Cross-bridged configurations move down chromosomes via branch migration, resulting in longer heteroduplex regions.
- Formation of the chi-form/Holliday structure precedes additional endonuclease nicking and final ligation, completing recombinant duplex formation.
- Key protein involved is RecA in homologous recombination.
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Description
This quiz focuses on the various DNA polymerases and their roles in DNA replication and repair mechanisms. It delves into the specific functions of DNA polymerase III, as well as the proofreading capabilities of DNA enzymes. Understand the significance of these processes in prokaryotic cells.