DNA Replication Quiz

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Questions and Answers

What is the name of the short, double-stranded region with a free OH group on the 3' end of the short strand, which is required for DNA polymerase to initiate synthesis?

  • Leading Strand
  • Okazaki Fragment
  • Lagging Strand
  • Primer (correct)

What is the name of the enzyme that catalyzes DNA chain elongation during replication?

  • RNA Polymerase
  • DNA Helicase
  • Ligase
  • DNA Polymerase III (correct)

Which of the following statements is TRUE about the lagging strand?

  • It is always longer than the leading strand.
  • It is synthesized discontinuously in the direction away from the replication fork. (correct)
  • It is synthesized using only one primer.
  • It is synthesized continuously in the direction of the replication fork.

Why is the leading strand synthesized continuously while the lagging strand is synthesized discontinuously?

<p>The leading strand is synthesized in the direction of the replication fork, while the lagging strand is synthesized in the opposite direction. (C)</p> Signup and view all the answers

Which of the following describes the role of helix destabilizing proteins (HD proteins) in DNA replication?

<p>They unwind the DNA helix ahead of the replication fork. (C)</p> Signup and view all the answers

What is the role of DNA helicase in DNA replication?

<p>To unwind the DNA double helix. (B)</p> Signup and view all the answers

How does the binding of HD proteins to single-stranded DNA shift the equilibrium towards single-stranded DNA?

<p>They destabilize the double-stranded DNA structure, making it easier to separate. (A)</p> Signup and view all the answers

Why is it necessary for DNA replication to be bidirectional?

<p>To ensure that both strands of DNA are replicated simultaneously and efficiently. (A)</p> Signup and view all the answers

In what direction does the new DNA strand grow during DNA replication?

<p>5' to 3' (D)</p> Signup and view all the answers

What is the function of the free 3' OH group of the primer in DNA replication?

<p>It provides a starting point for DNA polymerase to add nucleotides. (D)</p> Signup and view all the answers

What is the role of the origin of replication (Ori) in the initiation of DNA replication?

<p>It provides a starting point for the unwinding of the DNA helix. (D)</p> Signup and view all the answers

How do HD proteins facilitate the separation of parental DNA strands during replication?

<p>They bind to the single strands of DNA and prevent them from re-annealing. (B)</p> Signup and view all the answers

What is the role of the deoxyribonucleoside triphosphates (dATP, dTTP, dCTP, and dGTP) in DNA replication?

<p>They provide the building blocks for the new DNA strand. (C)</p> Signup and view all the answers

Which of the following statements about HD proteins is NOT true?

<p>They act as enzymes to unwind the DNA helix. (A)</p> Signup and view all the answers

In eukaryotes, how does the presence of multiple origins of replication contribute to the replication process?

<p>It allows for faster replication of the larger eukaryotic genome. (A)</p> Signup and view all the answers

How does the movement of the replication fork along the DNA contribute to the replication process?

<p>It allows for the creation of two new daughter DNA molecules. (D)</p> Signup and view all the answers

Which of the following is NOT a characteristic of DNA helicases?

<p>They can reversibly cut a single strand of the double helix. (B)</p> Signup and view all the answers

What is the primary role of Type I DNA Topoisomerases?

<p>To relieve accumulated super-twists in the DNA helix by creating a transient nick. (C)</p> Signup and view all the answers

What is the main difference between Type I and Type II DNA topoisomerases?

<p>Type I topoisomerases create a nick in one strand of DNA while Type II create a nick in both strands. (B)</p> Signup and view all the answers

Which enzyme is responsible for synthesizing the new DNA strand in the 5' → 3' direction?

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

What is the role of primase in DNA replication?

<p>To synthesize short RNA primers that provide a starting point for DNA polymerase. (B)</p> Signup and view all the answers

Why is the lagging strand synthesized discontinuously in Okazaki fragments?

<p>Because DNA polymerase can only add nucleotides to the 3' end of a growing strand. (C)</p> Signup and view all the answers

What is the function of SSB proteins in DNA replication?

<p>To prevent the separated strands of DNA from re-annealing. (C)</p> Signup and view all the answers

Which of the following enzymes is NOT involved in DNA replication?

<p>RNA polymerase II (C)</p> Signup and view all the answers

What is the main purpose of 3'→5' exonuclease activity in DNA polymerase III?

<p>To remove incorrectly paired nucleotides from the newly synthesized strand. (A)</p> Signup and view all the answers

Which of the following is NOT a consequence of errors in DNA replication?

<p>Increased rate of cell division. (C)</p> Signup and view all the answers

What is the role of nucleotide analogues in DNA replication?

<p>They can block DNA chain growth, inhibiting cell division. (C)</p> Signup and view all the answers

Why is it crucial for DNA polymerase III to have both 5'→3' polymerase activity and 3'→5' exonuclease activity?

<p>To ensure that the new DNA strand is complementary to the template strand. (C)</p> Signup and view all the answers

What is the significance of DNA polymerase III's ability to hydrolytically remove mismatched nucleotides?

<p>It prevents the accumulation of errors in the newly synthesized DNA strand. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the difference between the leading and lagging strands in DNA replication?

<p>The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously. (A)</p> Signup and view all the answers

What is the primary function of the HD Protein Helicase in DNA replication?

<p>To unwind the DNA helix and separate the strands. (D)</p> Signup and view all the answers

What is the role of the template strand in DNA replication?

<p>It acts as a guide for the synthesis of the new DNA strand. (D)</p> Signup and view all the answers

What activity allows DNA polymerase I to remove RNA primers during DNA synthesis?

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

Which activity of DNA polymerase III is crucial for proofreading newly synthesized DNA?

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

What is the primary function of DNA polymerase I in the context of RNA primers?

<p>Remove RNA primers and replace with DNA (A)</p> Signup and view all the answers

Which direction does DNA polymerase I synthesize DNA?

<p>5’ to 3’ direction (A)</p> Signup and view all the answers

What sequence of events occurs when DNA polymerase III encounters an RNA primer?

<p>It excises the RNA primer and stops synthesis. (B)</p> Signup and view all the answers

What type of nucleotides does DNA polymerase I use to fill the gap left after removing RNA primers?

<p>Deoxyribonucleotides (D)</p> Signup and view all the answers

In the context of DNA synthesis, what is the role of the 3’→5’ exonuclease activity?

<p>To degrade mismatched or improperly paired nucleotides (C)</p> Signup and view all the answers

Which enzyme is responsible for continuing DNA synthesis until blocked by an RNA primer?

<p>DNA polymerase III (C)</p> Signup and view all the answers

What is the primary function of 5'→3' exonuclease activity of DNA polymerase I?

<p>It removes nucleotides from a properly base paired region of DNA. (D)</p> Signup and view all the answers

What role does DNA ligase play in the DNA replication process?

<p>It catalyzes the linkage between DNA chains synthesized by different polymerases. (A)</p> Signup and view all the answers

Which statement accurately describes the activity of DNA polymerase β (Beta)?

<p>It participates in editing and repair of DNA. (A)</p> Signup and view all the answers

The process of removing mismatched ends during DNA replication is primarily attributed to which activity?

<p>5'→3' exonuclease activity of DNA polymerase I (C)</p> Signup and view all the answers

Which statement is true regarding the energy requirements for DNA replication in humans?

<p>ATP is broken down to AMP and PPi to provide energy. (D)</p> Signup and view all the answers

What is the unique function of DNA polymerase Υ (Upsilon)?

<p>It is involved in mitochondrial DNA synthesis. (B)</p> Signup and view all the answers

What differentiates the activity of the 5'→3' exonuclease from the 3'→5' exonuclease in DNA polymerases?

<p>5'→3' removes nucleotides while 3'→5' edits and proofreads. (D)</p> Signup and view all the answers

Which of the following describes the consequence of RNA degradation during DNA synthesis?

<p>It enables gaps to be filled with DNA after RNA removal. (B)</p> Signup and view all the answers

Flashcards

Strand Separation

The process of unwinding and separating DNA strands for replication. It creates a template for DNA polymerases.

Replication Fork

The Y-shaped region where the DNA strands unwind and separate during replication.

Helix Destabilizing Proteins (HD Proteins)

Proteins that help separate DNA strands by preventing the double helix from re-forming.

Single Stranded DNA Binding Proteins (SSB)

Proteins that bind to single-stranded DNA to prevent it from re-joining or degrading.

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Origin of Replication (Ori)

The specific location on the DNA where replication begins; different in prokaryotes and eukaryotes.

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Leading Strand

The strand of DNA that is synthesized continuously in the direction of the replication fork.

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Lagging Strand

The strand of DNA synthesized in short segments away from the replication fork.

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DNA Polymerase

The enzyme responsible for adding nucleotides to a growing DNA strand during replication.

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DNA helicases

Enzymes that unwind DNA at the replication fork, using ATP for energy.

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SSB protein

Single-stranded binding protein that stabilizes single-stranded DNA during replication.

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DNA polymerase III

Main enzyme that synthesizes new DNA strands by adding nucleotides.

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Primase

Enzyme that synthesizes RNA primers necessary for DNA replication to begin.

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Type I topoisomerases

Enzymes that cut one strand of DNA, relieving supercoiling without using ATP.

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Type II topoisomerases

Enzymes that cut both strands of DNA, using ATP, and create negative super-twists.

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DNA synthesis direction

New DNA strands are synthesized in the 5' to 3' direction.

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Okazaki Fragments

Short segments of DNA synthesized on the lagging strand during replication.

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DNA Primer

A short, double-stranded segment that provides a free 3' OH group for DNA synthesis initiation.

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5' to 3' Direction

The direction in which the new DNA strand is synthesized, ensuring anti-parallel structure.

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Complementary Strand

A DNA strand that is complementary to the template strand, created during replication.

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Deoxyribonucleoside Triphosphates (dNTPs)

Building blocks required for DNA synthesis, including dATP, dTTP, dCTP, and dGTP.

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Leading vs Lagging Synthesis

Leading is continuous, while lagging is discontinuous with fragments called Okazaki.

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Anti-parallel Strands

The orientation of DNA strands running in opposite directions during replication.

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Nucleotide Analogues

Modified nucleotides that can block DNA chain growth and slow cell division.

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DNA Replication Fidelity

The accuracy of DNA replication; it aims to minimize errors in the nucleotide sequence.

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DNA Polymerase III Activities

Enzyme with 5’→3’ polymerase and 3’→5’ exonuclease (proofreading) activities.

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Proofreading Activity

The function of DNA polymerase III that corrects errors by removing incorrect nucleotides.

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Template Base Pairing

The correct matching of nucleotides to their complementary bases during DNA replication.

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Hydrolytic Removal

The process by which DNA Polymerase III removes incorrect nucleotides using water.

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Deleterious Mutations

Harmful changes in DNA sequence caused by errors during replication.

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Misreading the Template

Errors that occur when DNA Polymerase III incorrectly inserts nucleotides based on the template.

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3'→5' exonuclease activity

Activity of DNA polymerase that degrades improperly paired nucleotides from the end.

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5'→3' polymerase activity

DNA polymerase activity for adding nucleotides in the 5' to 3' direction.

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5'→3' exonuclease activity

Activity of DNA polymerase I that hydrolyzes RNA primers ahead of it.

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DNA synthesis proof reading

The process by which DNA polymerase checks and corrects errors during synthesis.

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Nick in DNA synthesis

A space between newly synthesized DNA and the RNA primer that needs filling.

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Leading & Lagging Strand

Leading is continuous synthesis; lagging is in Okazaki fragments away from fork.

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DNA Ligase

Enzyme that catalyzes the final linkage between DNA fragments by connecting 5' phosphate to 3' OH.

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DNA polymerase α (alpha)

An enzyme that synthesizes RNA primers on the lagging strand, also called primase.

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DNA polymerase β (beta)

An enzyme involved in DNA editing and repair processes.

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DNA polymerase Υ (upsilon)

A unique DNA polymerase found in mitochondria, involved in mitochondrial DNA replication.

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Final phosphodiester linkage

The connection made by DNA ligase between chains synthesized by DNA polymerases I and III.

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Energy for DNA ligation

During DNA ligation, energy is sourced from ATP cleavage to AMP and PPi.

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Study Notes

DNA and RNA Structure

  • DNA is a double helix, with antiparallel strands
  • Nucleotides are linked by phosphodiester bonds
  • A pairs with T, and G pairs with C (base pairing)
  • DNA strands have a 5' and 3' end
  • Hydrogen bonding holds base pairs together (A-T, G-C)
  • The distance between DNA base pairs is 0.34nm
  • RNA is single-stranded, and not a double helix
  • Nucleotides are also linked by phosphodiester bonds
  • A pairs with U, and G pairs with C (base pairing)
  • Different types of RNA exist, including mRNA, tRNA, rRNA

Erwin Chargaff's Rules

  • Chargaff's rules describe the consistent ratios of nitrogenous bases in DNA.
  • Rule #1: Guanine always pairs with cytosine, and adenine always pairs with thymine. These pairings occur in equal percentages
  • Rule #2: The proportions of DNA bases vary between species, although equal percentages of guanine + cytosine, and adenine + thymine hold true.

DNA Replication

  • DNA replication is semi-conservative
  • The two strands of DNA separate, and each serves as a template to synthesize a new complementary strand
  • Enzymes are involved in unwinding DNA(helicases), providing stabilization for the unwound DNA strands(SSB proteins) separating the single stranded DNA strands (DNA topoisomerases), adding nucleotides to the growing strands (DNA polymerases) and connecting the Okazaki fragments (DNA ligases).
  • Several different DNA polymerases are involved in replication, with differing functions in the process
  • Multiple origins of replication occur in eukaryotes, as opposed to a single origin of replication in prokaryotes.

RNA Polymerase, Transcription and translation

  • RNA polymerase synthesizes RNA from DNA
  • mRNA carries genetic information from DNA to ribosomes
  • rRNA is a component of ribosomes
  • tRNA transfers amino acids to the ribosome during protein synthesis

Other Important Figures and Concepts

  • Oswald Avery: His work was important to identify DNA as a transforming factor
  • Photo 51: A key X-ray diffraction image that helped determine the structure of DNA

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