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Questions and Answers
What characterizes the leading strand during DNA replication?
What characterizes the leading strand during DNA replication?
- Synthesized continuously towards the replication fork (correct)
- Formed primarily by DNA ligase
- Synthesized discontinuously in fragments
- Contains RNA primers that remain throughout replication
What are Okazaki fragments?
What are Okazaki fragments?
- The enzymes that catalyze DNA synthesis
- Short fragments of the lagging strand synthesized discontinuously (correct)
- Segments of the leading strand that are synthesized continuously
- RNA primers used to initiate DNA replication
Which enzyme is responsible for joining the sugar-phosphate backbone of Okazaki fragments?
Which enzyme is responsible for joining the sugar-phosphate backbone of Okazaki fragments?
- DNA polymerase III
- Helicase
- DNA ligase (correct)
- Primase
In which direction does the lagging strand elongate during DNA replication?
In which direction does the lagging strand elongate during DNA replication?
What role does DNA polymerase I play in the replication process?
What role does DNA polymerase I play in the replication process?
What does the semi-conservative model of DNA replication imply?
What does the semi-conservative model of DNA replication imply?
Which enzyme is primarily responsible for unwinding the DNA double helix during replication?
Which enzyme is primarily responsible for unwinding the DNA double helix during replication?
Which of the following correctly states the direction of DNA strand synthesis?
Which of the following correctly states the direction of DNA strand synthesis?
What is the role of the single-strand binding protein during DNA replication?
What is the role of the single-strand binding protein during DNA replication?
When does DNA replication begin?
When does DNA replication begin?
Which of the following statements about DNA replication is FALSE?
Which of the following statements about DNA replication is FALSE?
What is the first step in the process of DNA replication?
What is the first step in the process of DNA replication?
Which molecule helps in the synthesis of RNA primers during DNA replication?
Which molecule helps in the synthesis of RNA primers during DNA replication?
What is the primary function of helicase in the DNA replication process?
What is the primary function of helicase in the DNA replication process?
What role do single-strand binding proteins play during DNA replication?
What role do single-strand binding proteins play during DNA replication?
Which type of DNA polymerase is responsible for adding nucleotides to the RNA primer?
Which type of DNA polymerase is responsible for adding nucleotides to the RNA primer?
What is the primary function of DNA ligase in the DNA replication process?
What is the primary function of DNA ligase in the DNA replication process?
What does primase do in the context of DNA replication?
What does primase do in the context of DNA replication?
How does topoisomerase assist in the process of DNA replication?
How does topoisomerase assist in the process of DNA replication?
What is the significance of the 3’ end of a DNA strand during replication?
What is the significance of the 3’ end of a DNA strand during replication?
What initiates the process of DNA replication?
What initiates the process of DNA replication?
What is the primary function of helicase during DNA replication?
What is the primary function of helicase during DNA replication?
Why is the RNA primer necessary in DNA synthesis?
Why is the RNA primer necessary in DNA synthesis?
Which enzyme is responsible for relieving the twisting strain ahead of the replication fork?
Which enzyme is responsible for relieving the twisting strain ahead of the replication fork?
In which direction does DNA polymerase III synthesize the new DNA strand?
In which direction does DNA polymerase III synthesize the new DNA strand?
What role do single-strand binding proteins play during DNA replication?
What role do single-strand binding proteins play during DNA replication?
What is the approximate length of the RNA primer formed during DNA replication?
What is the approximate length of the RNA primer formed during DNA replication?
What occurs at the replication fork during DNA replication?
What occurs at the replication fork during DNA replication?
What happens after the RNA primer is synthesized during DNA replication?
What happens after the RNA primer is synthesized during DNA replication?
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Study Notes
DNA Replication Process
- Replication begins at the origin of replication, forming a replication bubble.
- Helicase unwinds the double helix by breaking hydrogen bonds, creating a replication fork.
- Single-strand binding proteins keep the separated parental strands apart to prevent re-pairing.
- Topoisomerase alleviates strain caused by the unwinding of the double helix.
Template Strands
- Each parental strand serves as a template for synthesizing a new complementary strand.
- DNA polymerase III adds free DNA nucleotides to the 3’ end of an RNA primer which complements the template strand.
- RNA primer, a short segment of 5 to 10 nucleotides, is synthesized by primase, as DNA polymerase cannot initiate strand synthesis.
Directionality of Synthesis
- DNA replication occurs in a 5’ to 3’ direction, with the leading strand synthesized continuously towards the replication fork.
- Lagging strand synthesis is discontinuous, occurring away from the replication fork in short segments known as Okazaki fragments.
Enzymes Involved
- Helicase: Unwinds DNA strands.
- Single-strand binding protein: Prevents re-pairing of separated strands.
- Topoisomerase: Relieves tension ahead of the replication fork.
- Primase: Synthesizes RNA primers complementary to template strands.
- DNA polymerase III: Responsible for adding nucleotides to growing DNA chains.
- DNA polymerase I: Replaces RNA primers with DNA nucleotides.
- DNA ligase: Joins Okazaki fragments into a continuous strand.
Semi-Conservative Model
- Each daughter DNA molecule consists of one original (parental) strand and one new strand.
- Semi-conservative replication ensures one strand in each new helix is from the original DNA, maintaining genetic integrity.
Basic Rules of DNA Replication
- Semi-conservative: Each replicated DNA consists of one old and one new strand.
- Origin of replication: Initiates the replication process.
- 5’ to 3’ synthesis: New strands are always formed in this direction.
- Primers are required: RNA primers provide starting points for DNA synthesis.
- Replication can be either unidirectional or bidirectional.
Okazaki Fragments
- Lagging strand synthesis produces short DNA fragments known as Okazaki fragments joined by DNA ligase to form a continuous DNA strand.
Result of DNA Replication
- Two identical copies of the original DNA are produced at the end of the replication process.
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