24 Questions
What is the role of DNA polymerase I in lagging strand synthesis?
To remove the RNA primers and replace them with DNA
What are the short segments of DNA synthesized during lagging strand synthesis called?
Okazaki fragments
What is the role of DNA ligase in DNA replication?
To join the Okazaki fragments together
During leading strand synthesis, DNA polymerase synthesizes the new DNA strand in which direction?
5' to 3' direction
What is the purpose of the RNA primer during lagging strand synthesis?
To initiate the synthesis of an Okazaki fragment
What happens to the RNA primer after the synthesis of an Okazaki fragment?
It is removed by DNA polymerase I
What is the role of primase during lagging strand synthesis?
To synthesize the RNA primer
What is the result of the combination of leading strand synthesis and lagging strand synthesis?
One continuous DNA strand
What is the main obstacle in DNA polymerase during leading strand synthesis?
The need for 3'-OH to build on
What is the role of RNA polymerase in DNA synthesis?
To form the RNA primer
What is the characteristic of Okazaki fragments?
They are 100-200 nucleotides in length in humans
Why is DNA ligase not necessary during leading strand synthesis?
Because the leading strand is synthesized continuously
What is the consequence of DNA polymerase incorporating a non-complementary nucleotide during synthesis?
The DNA strand is prone to mutations
What is the significance of the RNA primer during DNA synthesis?
It provides a 3'-OH group for DNA polymerase to build on
Why is DNA polymerase necessary for lagging strand synthesis?
Because it synthesizes the lagging strand discontinuously
What is the purpose of DNA primase in DNA synthesis?
To form the RNA primer for DNA synthesis
What is the direction of DNA synthesis by DNA Polymerase?
5' to 3'
What is unique about the DNA synthesis in eukaryotic cells compared to bacterial cells?
It occurs at multiple sites
What is the function of the 3' -OH group in DNA synthesis?
To add onto the growing strand of DNA
What is the result of the breakage of the phosphoanhydride bond in DNA synthesis?
Release of pyrophosphate
What is the orientation of the strands in a double-stranded DNA molecule?
Antiparallel
What is necessary for DNA synthesis to occur?
A 3' -OH group
What is the result of the mechanism of catalysis during DNA synthesis?
Incorporation of a monophosphate
What is the substrate for DNA synthesis?
Deoxynucleoside triphosphates
Study Notes
DNA Replication
- DNA replication occurs in the 5' to 3' direction.
- It begins at one origin (Ori) site in bacteria and at multiple sites in eukaryotic cells.
Lagging Strand Synthesis
- Synthesized discontinuously in short segments called Okazaki fragments, each initiated by an RNA primer.
- RNA primer is later elongated by DNA polymerase.
- DNA polymerase disengages and re-engages at a new primer upon reaching the next RNA primer.
- The DNA template loops to ensure both polymerases move in the same direction.
Leading Strand Synthesis
- Synthesized continuously in the 5' to 3' direction by DNA polymerase.
Fragment Maturation
- RNA primers are removed by DNA polymerase I.
- Gaps are filled with DNA by DNA polymerase I.
- Okazaki fragments are joined by DNA ligase to form a continuous DNA strand.
DNA Polymerase
- Synthesizes DNA in the 5' to 3' direction.
- Has proofreading ability.
- Requires a 3' OH group to add onto.
- Reads the template DNA in the 3' to 5' direction.
Mechanism of Catalysis
- The 3' OH of the last nucleotide attacks the phosphate of the incoming nucleotide (triphosphate).
- Substrates are deoxynucleoside triphosphates.
- Breaks the phosphoanhydride bond in the nucleotide and forms a phosphodiester bond.
Overcoming Obstacles in DNA Polymerase
- DNA polymerase can only extend an existing chain and needs a 3' OH group to build on.
- Solution: Use RNA polymerase (DNA primase) to make a short RNA primer, which provides a 3' OH group for DNA polymerase to build on.
Learn about the steps involved in DNA replication, including the synthesis of the lagging strand, the role of DNA polymerase I, and the formation of a continuous DNA strand.
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