-DNA REPLICATION-KIM

Which model of DNA replication is biologically significant?

• A. Conservative

• B. Dispersive

• C. Semiconservative

• D. Fragmentary
  
  

• Answer: C. Semiconservative
  Explanation: The semiconservative model, confirmed by the Meselson and Stahl experiment, ensures each daughter DNA molecule contains one old strand and one new strand.

Which enzyme unwinds the DNA helix during replication?

• A. DNA Polymerase

• B. Helicase

• C. Topoisomerase

• D. Ligase
  
  

• Answer: B. Helicase
  Explanation: Helicase breaks hydrogen bonds between base pairs, separating the two strands of DNA.

What is the function of DNA ligase in DNA replication?

• A. Unwinds DNA strands.

• B. Seals gaps between Okazaki fragments.

• C. Synthesizes RNA primers.

• D. Removes mismatched nucleotides.
  
  

• Answer: B. Seals gaps between Okazaki fragments.
  Explanation: DNA ligase creates phosphodiester bonds to join fragments on the lagging strand.

• Which phase of the cell cycle involves DNA replication?

  • A. G1 phase

  • B. S phase

  • C. G2 phase

  • D. M phase
    
    

  
  

• Answer: B. S phase
  Explanation: DNA replication occurs during the S (synthesis) phase of the cell cycle.

1. What is the function of telomerase?

   • A. Proofreading DNA during replication.

   • B. Adding repetitive sequences to chromosome ends.

   • C. Removing RNA primers.

   • D. Synthesizing Okazaki fragments.
     
     

• Answer: B. Adding repetitive sequences to chromosome ends.
  Explanation: Telomerase prevents chromosome shortening by extending the 3′ ends of DNA.

• Which enzyme synthesizes RNA primers during DNA replication?

  • A. DNA Polymerase

  • B. Helicase

  • C. Primase

  • D. Ligase
    
    

• Answer: C. Primase
  Explanation: Primase synthesizes short RNA primers to provide a starting point for DNA polymerase during replication.

What are Okazaki fragments?

• A. Fragments of damaged DNA.

• B. Short DNA sequences synthesized on the lagging strand.

• C. RNA sequences removed during termination.

• D. Double-stranded DNA molecules formed after replication.
  
  

• Answer: B. Short DNA sequences synthesized on the lagging strand.
  Explanation: Okazaki fragments are synthesized discontinuously on the lagging strand and later joined by DNA ligase.

Which enzyme prevents supercoiling during DNA replication?

• A. Helicase

• B. Topoisomerase

• C. Ligase

• D. Telomerase
  
  

• Answer: B. Topoisomerase
  Explanation: Topoisomerase prevents overwinding ahead of the replication fork by making transient cuts in the DNA.

What is the primary DNA polymerase in prokaryotic replication?

• A. DNA Pol I

• B. DNA Pol II

• C. DNA Pol III

• D. DNA Pol α
  
  

• Answer: C. DNA Pol III
  Explanation: DNA Pol III is the main enzyme responsible for synthesizing new DNA strands in prokaryotes.

Which molecule is targeted by fluoroquinolones, such as ciprofloxacin?

• A. DNA polymerase

• B. Helicase

• C. DNA gyrase

• D. Ligase
  
  

• Answer: C. DNA gyrase
  Explanation: Fluoroquinolones inhibit DNA gyrase, an essential enzyme for relieving supercoiling in bacterial DNA

Regarding DNA replication models:
A. The semiconservative model involves one old and one new strand in daughter DNA.
B. The conservative model creates two identical DNA molecules, each with old strands.
C. The dispersive model involves interspersed new and old DNA in both strands.
D. The Meselson-Stahl experiment supported the conservative model.
E. The semiconservative model is biologically significant.

• A. The semiconservative model involves one old and one new strand in daughter DNA. (True)
  B. The conservative model creates two identical DNA molecules, each with old strands. (True)
  C. The dispersive model involves interspersed new and old DNA in both strands. (True)
  D. The Meselson-Stahl experiment supported the conservative model. (False)
  E. The semiconservative model is biologically significant. (True)

  
  

Regarding the replication fork:
A. Helicase unwinds the DNA strands.
B. SSBPs prevent reannealing of separated strands.
C. The leading strand is synthesized discontinuously.
D. The lagging strand requires multiple primers.
E. DNA synthesis occurs in the 3′ → 5′ direction.

A. Helicase unwinds the DNA strands. (True)
B. SSBPs prevent reannealing of separated strands. (True)
C. The leading strand is synthesized discontinuously. (False)
D. The lagging strand requires multiple primers. (True)
E. DNA synthesis occurs in the 3′ → 5′ direction. (False)

• Regarding DNA polymerases:
  A. DNA Pol III is the main polymerase in prokaryotic replication.
  B. DNA Pol I removes RNA primers and replaces them with DNA.
  C. DNA Pol α is involved in mitochondrial DNA replication.
  D. DNA Pol δ synthesizes the leading strand in eukaryotes.
  E. All DNA polymerases have proofreading activity.

  
  

• A. DNA Pol III is the main polymerase in prokaryotic replication. (True)
  B. DNA Pol I removes RNA primers and replaces them with DNA. (True)
  C. DNA Pol α is involved in mitochondrial DNA replication. (False)
  D. DNA Pol δ synthesizes the leading strand in eukaryotes. (True)
  E. All DNA polymerases have proofreading activity. (False)

  
  

Regarding the enzymes in DNA replication:
A. Ligase joins Okazaki fragments on the lagging strand.
B. Helicase prevents supercoiling during replication.
C. Topoisomerase relieves torsional stress on DNA.
D. Primase synthesizes RNA primers.
E. Telomerase is active in all somatic cells.

A. Ligase joins Okazaki fragments on the lagging strand. (True)
B. Helicase prevents supercoiling during replication. (False)
C. Topoisomerase relieves torsional stress on DNA. (True)
D. Primase synthesizes RNA primers. (True)
E. Telomerase is active in all somatic cells. (False)

Regarding telomeres and their replication:
A. Telomeres are repetitive sequences at the ends of chromosomes.
B. Telomerase adds sequences to the 5′ ends of DNA.
C. Telomeres shorten with each round of replication in most somatic cells.
D. Telomerase is highly active in cancer cells.
E. Telomere shortening contributes to aging.

A. Telomeres are repetitive sequences at the ends of chromosomes. (True)
B. Telomerase adds sequences to the 5′ ends of DNA. (False)
C. Telomeres shorten with each round of replication in most somatic cells. (True)
D. Telomerase is highly active in cancer cells. (True)
E. Telomere shortening contributes to aging. (True)

Regarding replication origins:
A. Prokaryotes have multiple origins of replication.
B. Eukaryotic replication origins are AT-rich sequences.
C. Helicase binds to the origin to initiate unwinding of DNA strands.
D. Replication forks are bidirectional from the origin.
E. Origin sequences in prokaryotes are called OriC.

A. Prokaryotes have multiple origins of replication. (False)
B. Eukaryotic replication origins are AT-rich sequences. (True)
C. Helicase binds to the origin to initiate unwinding of DNA strands. (True)
D. Replication forks are bidirectional from the origin. (True)
E. Origin sequences in prokaryotes are called OriC. (True)

Regarding the lagging strand:
A. Synthesis occurs in the 3′ → 5′ direction.
B. It requires multiple RNA primers.
C. Okazaki fragments are formed during lagging strand synthesis.
D. DNA ligase is essential to join fragments on the lagging strand.
E. The lagging strand is synthesized continuously.

A. Synthesis occurs in the 3′ → 5′ direction. (False)
B. It requires multiple RNA primers. (True)
C. Okazaki fragments are formed during lagging strand synthesis. (True)
D. DNA ligase is essential to join fragments on the lagging strand. (True)
E. The lagging strand is synthesized continuously. (False)

Regarding the replication machinery:
A. DNA replication is highly accurate due to proofreading by DNA polymerase.
B. Primase synthesizes DNA primers for replication.
C. Topoisomerase prevents overwinding of DNA during replication. (True)
D. Single-strand binding proteins stabilize separated DNA strands. (True)
E. DNA ligase synthesizes new DNA strands. (False)

A. DNA replication is highly accurate due to proofreading by DNA polymerase. (True)
B. Primase synthesizes DNA primers for replication. (False)
C. Topoisomerase prevents overwinding of DNA during replication. (True)
D. Single-strand binding proteins stabilize separated DNA strands. (True)
E. DNA ligase synthesizes new DNA strands. (False)

Regarding termination of replication:
A. Prokaryotic replication ends at specific termination sequences.
B. Eukaryotic replication ends when replication forks meet.
C. Telomeres are replicated by DNA polymerase.
D. Telomerase prevents the loss of coding DNA at chromosome ends.
E. Replication always terminates at telomeres in eukaryotes.

A. Prokaryotic replication ends at specific termination sequences. (True)
B. Eukaryotic replication ends when replication forks meet. (True)
C. Telomeres are replicated by DNA polymerase. (False)
D. Telomerase prevents the loss of coding DNA at chromosome ends. (True)
E. Replication always terminates at telomeres in eukaryotes. (True)

What is the significance of the semiconservative model in DNA replication?

Answer: The semiconservative model ensures that each daughter DNA molecule contains one parental strand and one newly synthesized strand, maintaining genetic continuity.
Explanation: This mechanism reduces replication errors and ensures faithful transmission of genetic information.

How does the lagging strand differ from the leading strand in replication?

Answer: The lagging strand is synthesized discontinuously in the 5′ → 3′ direction as Okazaki fragments, while the leading strand is synthesized continuously.
Explanation: DNA polymerase can only add nucleotides in the 5′ → 3′ direction, requiring multiple primers for the lagging strand

What role does DNA gyrase play in prokaryotic DNA replication?

Answer: DNA gyrase relieves supercoiling ahead of the replication fork by making temporary cuts in the DNA strands.
Explanation: Without DNA gyrase, the unwinding of DNA by helicase would create torsional strain, hindering replication.

Why is telomerase important in DNA replication?

Answer: Telomerase adds repetitive sequences to the ends of linear chromosomes, preventing the loss of essential genetic material during replication.
Explanation: This enzyme is crucial for maintaining chromosomal integrity, particularly in germ cells, stem cells, and cancer cells.

What is the role of RNA primers in DNA replication?

Answer: RNA primers provide the starting point for DNA polymerase to synthesize new DNA strands.
Explanation: DNA polymerase cannot initiate synthesis de novo; it requires a free 3′-OH group provided by the primer.