22 Questions
How many replication bubbles do prokaryotes typically have?
One
In what direction does DNA synthesis proceed with respect to the new daughter strand?
5' - 3'
What are Okazaki fragments?
Short fragments of DNA produced by discontinuous synthesis on the lagging strand
Which enzyme is responsible for adding nucleotides to a growing DNA strand?
DNA polymerase
Which of the following statements is true about eukaryotic DNA replication?
Eukaryotes have several replication bubbles
What role does the DNA polymerase play in DNA replication?
It adds nucleotides to the growing DNA strand
Where does DNA replication begin?
At the origin of replication
What is produced by RNA primase during DNA replication?
RNA primers
Which enzyme extends DNA on the leading strand?
DNA polymerase III
What are the short fragments synthesized on the lagging strand called?
Okazaki fragments
Which enzyme removes the RNA primer during DNA replication?
DNA polymerase I
What is the role of DNA ligase in DNA replication?
It joins Okazaki fragments
Which statement is true about the replication fork?
It is where the strands of DNA separate
During which step is the 2nd Okazaki fragment synthesized?
Further untwisting and elongation
What is the term for DNA replication that results in each new DNA molecule containing one original strand and one new strand?
Semi-conservative
What provides the catalysis for the 3' hydroxyl group to attack the phosphate of a 5'-deoxynucleoside triphosphate?
DNA polymerase
Which enzyme removes a 'turn' of the DNA and is a critical target for antibiotics?
Topoisomerase
Which enzyme is responsible for breaking hydrogen bonds between complementary base pairs during DNA replication?
DNA helicase
What is required for DNA polymerase to initiate synthesis?
Both a template strand and a primer
Which of these is a function of RNA primase in DNA replication?
Synthesizing a short RNA primer
Which of these is NOT a factor involved in DNA replication?
RNA template
Which of the following enzymes seals the backbone of DNA during DNA replication?
DNA ligase
Study Notes
DNA Replication
The Replication Bubble
- DNA replication occurs in a bidirectional manner, resulting in a replication bubble
- Prokaryotes have one replication bubble, while eukaryotes have multiple
- Two replication forks moving in opposite directions form a replication bubble
Mechanisms of DNA Synthesis
- DNA synthesis occurs in two directions: leading strand and lagging strand
- Leading strand synthesis is continuous, whereas lagging strand synthesis is discontinuous
- Nucleotides are added 5' - 3' along the new daughter strand
- DNA polymerase reads 3' - 5' along the leading strand from the RNA primer
DNA Polymerase
- DNA polymerase can only add nucleotides to a growing polymer
- Part of the replisome complex with other proteins such as PCNA
Process of DNA Replication
- The process begins with the unwinding of the double helix at the origin of replication
- RNA primase synthesizes a short RNA primer, which is later removed and replaced by DNA
- DNA polymerase III extends the DNA strands
- Okazaki fragments are formed on the lagging strand
- DNA polymerase I removes the RNA primer and replaces it with DNA
- DNA ligase joins the adjacent DNA fragments
Okazaki Fragments
- Short fragments of DNA produced by discontinuous synthesis on the lagging strand
- DNA synthesis on the lagging strand is discontinuous, resulting in Okazaki fragments
Enzymes Involved
- DNA Gyrase or Topoisomerase: removes 'turns' of DNA, critical target for blocking cell replication
- DNA Helicase: breaks hydrogen bonds between complementary base pairs, forming the replication fork
- Single strand binding protein: maintains the stability of the replication fork
- RNA Polymerase (RNA Primase): synthesizes a short RNA primer
- DNA Polymerase: synthesizes DNA strands
- DNA Ligase: joins adjacent DNA fragments
DNA Gyrase
- A topoisomerase II enzyme that causes a double-strand break and loops one strand under another
- Removes a 'turn' of DNA, critical for cell replication
DNA Helicase
- Breaks hydrogen bonds between complementary base pairs, forming the replication fork
- Maintains the stability of the replication fork with single strand binding proteins
RNA Primase
- Synthesizes a short RNA primer, which is later removed and replaced by DNA
- Follows base pairing rules (A-U), later replaced by DNA and sealed by DNA ligase
This quiz covers the DNA replication process, including the replication bubble, bidirectional synthesis, and the mechanics of DNA synthesis in prokaryotes and eukaryotes.
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