DNA Replication Quiz

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Questions and Answers

Which enzyme unwinds the parental double helix at the replication fork?

  • Primase
  • Helicase (correct)
  • DNA polymerase I
  • DNA ligase

In which direction is the leading strand synthesized?

  • It varies
  • Both directions
  • 5' to 3' (correct)
  • 3' to 5'

What are the short fragments of DNA synthesized on the lagging strand called?

  • Telomeres
  • Kinetochores
  • Okazaki fragments (correct)
  • Replication forks

Which enzyme synthesizes RNA primers during DNA replication?

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

What does DNA polymerase require to begin synthesizing a new DNA strand?

<p>A pre-existing chain (primer) (B)</p> Signup and view all the answers

Which enzyme creates the primer required for DNA replication?

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

Which enzyme joins Okazaki fragments together?

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

Which strand is synthesized continuously during DNA replication?

<p>Leading strand (B)</p> Signup and view all the answers

In which direction does DNA polymerase III synthesize the leading strand?

<p>5' → 3' (C)</p> Signup and view all the answers

Which enzyme removes RNA primers and replaces them with DNA nucleotides?

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

What are the short fragments synthesized on the lagging strand called?

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

Which of the following stabilizes unwound DNA strands during replication?

<p>Single-strand binding proteins (A)</p> Signup and view all the answers

Which of the following describes the orientation of the two DNA strands in a double helix?

<p>Antiparallel (C)</p> Signup and view all the answers

What is the main function of DNA polymerase?

<p>Adding nucleotides to a growing DNA strand (D)</p> Signup and view all the answers

Which enzyme synthesizes the new DNA strand?

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

On which strand are Okazaki fragments found?

<p>Lagging strand (A)</p> Signup and view all the answers

On which strand, leading or lagging, is DNA synthesized continuously?

<p>Leading strand (A)</p> Signup and view all the answers

In what direction does DNA polymerase add nucleotides?

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

How many DNA molecules are found in a human somatic cell's nucleus?

<p>46 (B)</p> Signup and view all the answers

What is the approximate number of nucleotide pairs in the E. coli chromosome?

<p>4.6 million (C)</p> Signup and view all the answers

What is the error rate during DNA replication?

<p>One per 10 billion nucleotides (C)</p> Signup and view all the answers

Where does DNA replication begin?

<p>Origins of replication (C)</p> Signup and view all the answers

What is the shape of the E. coli chromosome?

<p>Circular (C)</p> Signup and view all the answers

What do proteins do at the origin of replication?

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

How does the number of replication origins differ between eukaryotic and bacterial chromosomes?

<p>Eukaryotic chromosomes have multiple, while bacterial chromosomes have one. (C)</p> Signup and view all the answers

What is the function of multiple replication bubbles in eukaryotic DNA replication?

<p>To speed up the copying of very long DNA molecules (A)</p> Signup and view all the answers

What is the function of helicase during DNA replication?

<p>Unwinding and separating parental DNA strands (A)</p> Signup and view all the answers

In which direction does replication proceed from each origin?

<p>In both directions (D)</p> Signup and view all the answers

What is the role of single-strand binding proteins in DNA replication?

<p>Stabilizing the unwound parental DNA strands (A)</p> Signup and view all the answers

What is the function of topoisomerase during DNA replication?

<p>Relieving strain ahead of the replication fork (B)</p> Signup and view all the answers

How many origins of replication do E. coli cells have?

<p>One (A)</p> Signup and view all the answers

What is the shape of the region where parental DNA strands are being unwound?

<p>Y-shaped (C)</p> Signup and view all the answers

Where do replication bubbles form in eukaryotes?

<p>At many sites along the linear chromosome (A)</p> Signup and view all the answers

What is the initial step in nucleotide excision repair?

<p>Detection of damaged DNA. (D)</p> Signup and view all the answers

Which enzyme removes the damaged section of DNA during nucleotide excision repair?

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

What molecule serves as a template during repair synthesis?

<p>The undamaged DNA strand (C)</p> Signup and view all the answers

Which enzyme seals the free end of the new DNA to the old DNA during nucleotide excision repair?

<p>DNA ligase (A)</p> Signup and view all the answers

What is a direct consequence of unrepaired thymine dimers in skin cells?

<p>Interference with DNA replication (D)</p> Signup and view all the answers

What is the function of the sliding clamp in DNA replication?

<p>Moves DNA pol III along the DNA template (B)</p> Signup and view all the answers

What is the role of DNA pol III?

<p>To synthesize a new DNA strand (A)</p> Signup and view all the answers

What is the initial step in lagging strand synthesis?

<p>Primase adds an RNA primer (B)</p> Signup and view all the answers

What are Okazaki fragments?

<p>Short DNA fragments synthesized on the lagging strand (B)</p> Signup and view all the answers

Which enzyme replaces RNA primers with DNA nucleotides on the lagging strand?

<p>DNA pol I (C)</p> Signup and view all the answers

Which protein unwinds the parental double helix at replication forks?

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

What is the role of DNA ligase in lagging strand synthesis?

<p>To join Okazaki fragments (D)</p> Signup and view all the answers

What is the function of single-strand binding protein?

<p>Stabilizing single-stranded DNA (A)</p> Signup and view all the answers

What serves as the starting point for DNA synthesis?

<p>An RNA primer (A)</p> Signup and view all the answers

Which enzyme relieves overwinding strain ahead of replication forks?

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

What is the role of primase in DNA replication?

<p>Synthesizing an RNA primer (B)</p> Signup and view all the answers

Which enzyme is crucial for synthesizing both leading and lagging strands?

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

Which enzyme synthesizes new DNA strands by adding nucleotides to an RNA primer?

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

What determines the template for new strand synthesis?

<p>The existing DNA strand (C)</p> Signup and view all the answers

What does DNA polymerase I do during DNA replication?

<p>Removes RNA primers and replaces them with DNA (A)</p> Signup and view all the answers

What is the function of DNA ligase?

<p>Joining Okazaki fragments (C)</p> Signup and view all the answers

What is the shape of the sliding clamp protein?

<p>A doughnut (C)</p> Signup and view all the answers

The initial error rate of DNA replication is one in 100,000 nucleotides, but proofreading reduces it to one in how many nucleotides?

<p>10 billion (B)</p> Signup and view all the answers

What enzyme opens up the replication fork?

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

Which of these is NOT required for DNA replication?

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

What is the purpose of mismatch repair?

<p>To remove and replace incorrectly paired nucleotides after replication (B)</p> Signup and view all the answers

Which strand is synthesized discontinuously?

<p>The lagging strand (B)</p> Signup and view all the answers

What type of enzyme cuts damaged DNA strands during nucleotide excision repair?

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

Flashcards

Origin of replication in E. coli

E. coli has a single origin of replication for its circular chromosome.

Replication bubble

Formed when parental strands separate at the origin, allowing for replication forks to develop.

DNA replication direction

In E. coli, DNA replication moves in both directions from the origin until forks meet.

Eukaryotic origin of replication

Eukaryotes have multiple origins of replication along their linear chromosomes during S phase.

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Replication fork

A Y-shaped region where the parental DNA strands are unwound during replication.

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Helicases

Proteins that unwind and separate the parental DNA strands during replication.

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Single-strand binding proteins

Proteins that stabilize unwound parental DNA strands to prevent re-annealing.

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Topoisomerase

Enzyme that relieves strain ahead of the replication fork by breaking and rejoining DNA strands.

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Leading strand

The DNA strand synthesized continuously in the 5' to 3' direction.

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Lagging strand

The DNA strand synthesized in short fragments called Okazaki fragments in the 5' to 3' direction.

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Okazaki fragment

Short fragments of DNA synthesized on the lagging strand.

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DNA polymerase III (DNA pol III)

The enzyme that synthesizes new DNA strands during replication.

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DNA polymerase I (DNA pol I)

The enzyme that removes RNA primers and fills in gaps with DNA nucleotides.

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DNA ligase

An enzyme that joins Okazaki fragments together to form a continuous strand.

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Primase

An enzyme that synthesizes RNA primers needed for DNA replication to start.

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DNA replication complex

A large assembly of proteins that carries out DNA replication.

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DNA Polymerase

Enzyme that adds nucleotides to a growing DNA strand.

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Primer

Short RNA sequence providing a starting point for DNA synthesis.

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Antiparallel Elongation

Orientation where DNA strands run in opposite directions.

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Template Strand

The original DNA strand used as a guide for synthesis.

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DNA Replication Fork

Area where DNA unwinds and synthesis occurs.

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E. coli DNA

A single chromosome with about 4.6 million nucleotide pairs.

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Human somatic cells

Cells with 46 DNA molecules organized as chromosomes.

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Nucleotide pairs in humans

Approximately 6 billion nucleotide pairs in the human genome.

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DNA replication speed

Cells can copy DNA in a few hours with very few errors.

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Origins of replication

Specific DNA sequences where replication begins.

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Prokaryotic vs Eukaryotic replication

Both types use similar mechanisms but differ in scale and starting points.

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Error rate in DNA replication

Only about one error per 10 billion nucleotides during copying.

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Nucleotide excision repair

A process where enzymes detect and repair damaged DNA.

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Nuclease enzyme

An enzyme that cuts the damaged DNA strand at specific points.

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Repair synthesis

The process where DNA polymerase fills in missing nucleotides.

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Xeroderma pigmentosum (XP)

A condition caused by defects in nucleotide excision repair.

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DNA polymerase III

Enzyme that synthesizes new DNA strands by adding nucleotides.

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Sliding clamp

A protein that encircles the new DNA and moves DNA pol III along the template strand.

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Lagging strand synthesis steps

The series of actions during the formation of the lagging strand.

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RNA to DNA replacement

The process where DNA pol I replaces RNA primers with DNA nucleotides.

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5' to 3' direction

The orientation in which new DNA strands are synthesized.

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New strand elongation

The process of lengthening the new DNA strand during synthesis.

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DNA pol III

Synthesizes new DNA strands by adding nucleotides to primers.

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DNA pol I

Removes RNA primers and replaces them with DNA nucleotides.

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Mismatch repair

Enzyme system that removes and replaces incorrectly paired nucleotides.

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Proofreading

DNA polymerases check and correct base pairing errors during replication.

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Study Notes

DNA Replication

  • DNA replication is the process of copying DNA.
  • The process is remarkably accurate and fast.
  • More than a dozen enzymes and proteins participate in DNA replication.

Bacterial DNA Replication

  • Bacteria, like E. coli, have a single origin of replication on their circular chromosome.
  • Replication proceeds in both directions making a replication bubble.
  • Replication forks are formed and move away from the origin of replication
  • The process of replication is remarkably accurate only about one error per 10 billion nucleotides.

Eukaryotic DNA Replication

  • Eukaryotic chromosomes are linear, having multiple origins of replication.
  • Replication starts at many sites along the chromosome.
  • Replication bubbles form and expand, eventually fusing together to produce two daughter DNA molecules.
  • Replication occurs during the S phase of interphase in the cell cycle.

Leading Strand Synthesis

  • The leading strand is synthesized continuously in the 5' to 3' direction.
  • DNA polymerase III synthesize the leading strand.

Lagging Strand Synthesis

  • The lagging strand is synthesized discontinuously in short fragments (Okazaki fragments).
  • These fragments are then joined together by DNA ligase.
  • RNA primers are required for DNA polymerase III to begin synthesis of each Okazaki fragment.
  • DNA polymerase I removes RNA primers and replaces them with DNA nucleotides.

Proteins Involved in Replication

  • Helicase: Unwinds the parental double helix.
  • Single-strand binding proteins (SSBPs): Stabilize the unwound parental DNA strands.
  • Topoisomerase: Relieves strain in the DNA ahead of the replication fork.
  • Primase: Synthesizes RNA primers.
  • DNA polymerase III: Adds nucleotides to the 3' end of the RNA primer.
  • DNA polymerase I: Removes RNA primers and replaces them with DNA nucleotides.
  • DNA ligase: Joins Okazaki fragments together.

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