DNA Replication Quiz
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Questions and Answers

What is the primary role of DNA primase in DNA synthesis?

  • To stabilize the DNA double helix during synthesis
  • To add RNA primers to initiate DNA polymerization (correct)
  • To generate energy for the polymerization process
  • To remove errors introduced during DNA synthesis

Why can't DNA polymerase start polymerizing DNA directly?

  • It requires a DNA template strand first
  • It requires multiple RNA primers initially
  • It needs a free 3'OH group added by primase (correct)
  • It cannot recognize incoming nucleotides

What is the primary function of DNA polymerase I?

  • Elongates the leading strand
  • Substitutes for DNA polymerase II
  • Synthesizes RNA primers
  • Fills in small DNA segments during repair or replication (correct)

What happens to RNA primers after DNA synthesis is complete?

<p>They are removed and replaced with DNA (C)</p> Signup and view all the answers

Which DNA polymerase is responsible for synthesizing the lagging strand in eukaryotes?

<p>DNA polymerase δ (D)</p> Signup and view all the answers

What is one limitation of DNA primase during DNA synthesis?

<p>It lacks a self-correcting mechanism (C)</p> Signup and view all the answers

How does DNA polymerase ensure correct base pairing during DNA synthesis?

<p>By releasing energy from the hydrolysis of pyrophosphate (C)</p> Signup and view all the answers

What role does the sliding clamp protein play in DNA replication?

<p>It increases the processivity of DNA polymerase III (D)</p> Signup and view all the answers

How does DNA polymerase correct errors made during DNA replication?

<p>By using a 3’-5’ exonuclease activity (D)</p> Signup and view all the answers

Which statement about prokaryotic DNA replication is accurate?

<p>The catalytic core of DNA polymerase III synthesizes multiple daughter strands simultaneously. (D)</p> Signup and view all the answers

What forms the backbone of a DNA strand?

<p>Nucleotides linked by phosphodiester bonds (C)</p> Signup and view all the answers

Which enzyme is responsible for synthesizing RNA primers during DNA replication?

<p>DNA Primase (B)</p> Signup and view all the answers

What is the function of topoisomerase in DNA replication?

<p>To eliminate topological links and facilitate unwinding (A)</p> Signup and view all the answers

Why is DNA replication considered semiconservative?

<p>Each new DNA molecule contains one old strand and one new strand (A)</p> Signup and view all the answers

What is unique about the lagging strand during DNA replication?

<p>It is synthesized in fragments and not continuously (D)</p> Signup and view all the answers

What type of exonuclease activity does DNA Pol III possess?

<p>3’ to 5’ exonuclease activity (C)</p> Signup and view all the answers

What error rate does DNA replication achieve due to proofreading mechanisms?

<p>1 in every 1 billion base pairs (B)</p> Signup and view all the answers

What occurs immediately after an incorrect nucleotide is incorporated during DNA replication?

<p>Exonucleolytic proofreading occurs (A)</p> Signup and view all the answers

Which of the following statements is true regarding strand-directed mismatch repair?

<p>It identifies and repairs distortions due to non-complementary bases. (C)</p> Signup and view all the answers

What is the role of the 3’ to 5’ proofreading exonuclease in DNA Pol?

<p>To correct mismatched nucleotides at the primer terminus (A)</p> Signup and view all the answers

Flashcards

DNA Replication

The process by which a DNA molecule is duplicated, creating two identical copies.

Antiparallel Strands

The two strands of DNA run in opposite directions, with one strand going from 5' to 3' and the other going from 3' to 5'.

Chargaff's Rule

The rule that states that in DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

Semiconservative Replication

A type of DNA replication where each new DNA molecule is composed of one original strand and one newly synthesized strand.

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Semidiscontinuous Replication

A type of DNA replication where one strand is synthesized continuously (the leading strand) and the other is synthesized discontinuously (the lagging strand).

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3' to 5' exonuclease activity

The ability of DNA polymerase to remove mismatched nucleotides from the 3' end of a growing DNA strand.

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5' to 3' exonuclease activity

The ability of DNA polymerase to remove mispaired nucleotides from the 5' end of a growing DNA strand. This primarily helps remove RNA primers during DNA replication.

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Proofreading

The process by which mistakes made during DNA replication by DNA polymerase are corrected.

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Strand-directed mismatch repair

A mechanism that corrects errors in DNA replication that were not caught by DNA polymerase's proofreading activities.

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Nick

A break in a DNA strand, often found in newly synthesized DNA.

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What is the role of DNA polymerase I (Pol I)?

DNA polymerase I (Pol I) is primarily involved in repairing damaged DNA segments and removing RNA primers during replication. It has a 5'-3' exonuclease activity, meaning it can break down nucleotides from the 5' end of a DNA strand.

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What is the key role of DNA polymerase III (Pol III)?

DNA polymerase III (Pol III) is the main enzyme responsible for DNA replication. It synthesizes new DNA strands in the 5'-3' direction, adding nucleotides to the 3' end of the growing chain.

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What does the DNA polymerase α/primase complex do?

DNA polymerase α/primase complex is responsible for initiating the synthesis of both DNA strands during replication. It lays down short RNA primers that act as starting points for DNA synthesis.

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What is the function of a sliding clamp protein?

The sliding clamp protein acts like a clamp that keeps DNA polymerase (Pol III) firmly attached to the DNA strand during replication. This ensures that Pol III doesn't detach prematurely, enhancing its processivity.

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What does DNA ligase do?

DNA ligase acts as a molecular glue, joining the fragments of DNA synthesized on the lagging strand (Okazaki fragments) together. It forms a phosphodiester bond between the 3' hydroxyl group of one fragment and the 5' phosphate group of the next.

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What role does DNA primase play in DNA replication?

DNA polymerase, the enzyme responsible for building new DNA strands, requires a free 3' hydroxyl (OH) group to initiate synthesis. However, DNA polymerase cannot start from scratch. This is where DNA primase comes in. DNA primase adds short RNA sequences, called primers, to the DNA template strand, providing the necessary 3' OH group for DNA polymerase to begin building the new DNA strand.

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Why does DNA polymerase need to replace RNA primers?

DNA primase does not have a proofreading mechanism, so it makes more errors than DNA polymerase. However, these errors are quickly removed during the next step: DNA polymerase extends the primer, replacing the RNA with DNA and correcting any mistakes.

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Why is DNA primase less accurate than DNA polymerase?

DNA polymerase has a built-in proofreading mechanism, which allows it to correct mistakes during synthesis. This mechanism is not present in DNA primase.

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How does DNA polymerase build a new strand of DNA?

DNA polymerase synthesizes new DNA in the 5' to 3' direction, but it can only add nucleotides to an existing strand with a free 3' hydroxyl group. DNA primase provides those free 3' OH groups by adding short RNA primers to the template strand, allowing DNA polymerase to begin building the new DNA strand.

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What is the role of exonuclease activity in DNA polymerase?

DNA polymerase's exonuclease activity means it can remove nucleotides from the end of a strand, which is essential for correcting any mistakes made during DNA synthesis. This activity allows DNA to check its work and ensure accurate replication. Primase, on the other hand, lacks this proofreading capability, making it more prone to errors during the initial primer synthesis.

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Study Notes

DNA Replication

  • DNA replication is a semi-conservative process, producing two identical DNA molecules from one original DNA molecule.
  • Each new DNA molecule consists of one original strand and one new strand.
  • The process begins with the unwinding of the DNA double helix, creating a replication fork.
  • DNA helicases are responsible for disrupting hydrogen bonds to separate DNA strands.
  • Topoisomerases remove topological links between the two strands, facilitating unwinding.
  • DNA primase synthesizes short RNA primers to initiate DNA replication.
  • DNA polymerase synthesizes new DNA strands complementary to the template strand.
  • DNA polymerase III is the main enzyme for DNA replication, moves 5' to 3'.
  • Okazaki fragments are short DNA fragments formed on the lagging strand in the 5' to 3' direction.
  • DNA ligase joins Okazaki fragments together to create a continuous lagging strand.
  • DNA replication occurs in both directions in prokaryotes and eukaryotes.
  • DNA replication has specific origins in eukaryotes and prokaryotes.
  • DNA polymerase I is mainly involved in filling gaps and removing RNA primers during repair.
  • The initiation of DNA replication is dependent on pre-replicative complexes.
  • DNA helicases use ATP for propulsion along a DNA single strand to separate the double helix.
  • Single-strand DNA-binding proteins bind to single-stranded DNA behind helicase, preventing the DNA strands from reforming double strands.
  • Topoisomerase I produces a transient single-strand break in the DNA phosphodiester backbone to relieve the tension.
  • DNA polymerase has 3' to 5' exonuclease activity for error correction and proofreading as it goes.
  • DNA polymerase also has 5' to 3' exonuclease activity to remove RNA primer.
  • Mismatch repair systems are used to correct errors in newly synthesized DNA.
  • DNA polymerase error rate is approximately 1 in 100,000 base pairs, but the cell can correct these mistakes.
  • There are many enzymes involved in DNA replication and repair, each with specific functions.

DNA Repair

  • DNA repair mechanisms are vital for maintaining the integrity of the genome.
  • DNA repair systems can be classified into different pathways based on the types of damage.
  • Several different types of DNA damage can occur.
  • DNA repair mechanisms are important for correcting damage to the DNA structure.
  • Multiple pathways exist to address various types of DNA damage.
  • The high fidelity of replication is attributed to the initial base pairing and several “proofreading” mechanisms.
  • DNA repair can be further categorized as direct reversal of DNA damage, base excision repair (BER), nucleotide excision repair (NER), mismatch repair, homologous recombination (HR), and non-homologous end joining (NHEJ).

Types of DNA Damage and Repair

  • Depurination: Loss of a purine base (guanine or adenine) from DNA.
  • Deamination: Conversion of a cytosine to uracil, or an adenine to hypoxanthine.
  • Base Dimerization: Covalent linkage of adjacent thymine or cytosine bases, due to UV radiation.

Additional Information

  • Specific proteins and enzymes are involved in each DNA repair pathway.
  • Defects in DNA repair pathways can lead to various genetic diseases and an increased risk of cancer.

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Description

Test your knowledge on the key enzymes and processes involved in DNA replication. This quiz covers various aspects, including the functions of DNA primase, polymerases, and the role of RNA primers. Dive into the intricacies of replication in both prokaryotic and eukaryotic systems.

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