Identify the structure 1. Enzyme that unwinds DNA 2. Fragments of copied DNA created on the lagging strand 3. The strand that is copied in a continuous way, from the 3
to
direction 4. Binds Okazaki fragments 5. Builds a new DNA strand by adding complementary bases 6. Stabilizes the DNA molecule during replication by easing torsion upstream an downstream. 7. Strand that is copied discontinuously because it is traveling away from helicase 8. Initiates the synthesis DNA by creating a short RNA segment at replication fork 9. Place the events in the correct order: DNA polymerase adds nucleotides in the 5
‘
to 3
‘
direction Replication fork is formed DNA polymerase attaches to the primer Okazaki fragments are bound together by lgase DNA helicase unwinds DNA 10. Why is replication called “semi-conservative?”
The Correct Answer and Explanation is :
Answers
- Enzyme that unwinds DNA: Helicase
Helicase is responsible for breaking the hydrogen bonds between the DNA strands, creating the replication fork. - Fragments of copied DNA created on the lagging strand: Okazaki fragments
These are short, newly synthesized DNA fragments formed on the lagging strand during DNA replication. - The strand that is copied in a continuous way, from the 3′ to 5′ direction: Leading strand
The leading strand is synthesized continuously by DNA polymerase as it follows the unwinding of DNA. - Binds Okazaki fragments: Ligase
DNA ligase seals the nicks between Okazaki fragments, forming a continuous DNA strand. - Builds a new DNA strand by adding complementary bases: DNA polymerase
This enzyme adds nucleotides to the growing DNA strand during replication. - Stabilizes the DNA molecule during replication by easing torsion upstream and downstream: Topoisomerase
Topoisomerase prevents the DNA double helix from becoming too tightly coiled ahead of the replication fork. - Strand that is copied discontinuously because it is traveling away from helicase: Lagging strand
The lagging strand is synthesized in fragments because DNA polymerase can only add nucleotides in the 5′ to 3′ direction. - Initiates the synthesis of DNA by creating a short RNA segment at the replication fork: Primase
Primase synthesizes RNA primers to provide a starting point for DNA polymerase.
Correct Order of Events
- DNA helicase unwinds DNA.
- Replication fork is formed.
- Primase creates RNA primer.
- DNA polymerase attaches to the primer.
- DNA polymerase adds nucleotides in the 5′ to 3′ direction.
- Okazaki fragments are bound together by ligase.
Why is replication called “semi-conservative?”
DNA replication is termed “semi-conservative” because each daughter DNA molecule consists of one original (parental) strand and one newly synthesized strand. This method of replication ensures genetic continuity, as the parental strand serves as a template for the formation of the complementary new strand. By retaining one parental strand in each daughter molecule, the fidelity of DNA replication is maintained. The process also minimizes the likelihood of mutations and ensures that the genetic material is accurately passed on to subsequent generations. This mechanism was confirmed by the Meselson-Stahl experiment, which demonstrated the semi-conservative nature of DNA replication through density gradient centrifugation.