All Flashcards
What are the main steps of DNA replication?
- Unwinding the DNA (Helicase), 2. Preventing supercoiling (Topoisomerase & Single-Strand Binding Proteins), 3. Initiating synthesis with RNA primer (Primase), 4. Adding nucleotides (DNA Polymerase III), 5. Replacing RNA primer with DNA (DNA Polymerase I), 6. Sealing gaps (Ligase).
Describe the role of Helicase in DNA replication.
Helicase unwinds the DNA double helix by breaking hydrogen bonds between base pairs, creating a replication fork.
Describe the function of Primase during DNA replication.
Primase synthesizes a short RNA primer that provides a starting point for DNA polymerase to begin adding nucleotides.
What is the role of Ligase in DNA replication?
Ligase seals the gaps between Okazaki fragments on the lagging strand by forming phosphodiester bonds, creating a continuous DNA strand.
What is the function of Topoisomerase?
Topoisomerase relieves the torsional stress ahead of the replication fork by cutting and rejoining DNA strands, preventing supercoiling.
Describe the function of Single-Strand Binding Proteins.
Single-strand binding proteins bind to single-stranded DNA near the replication fork to prevent strands from re-annealing or forming secondary structures.
What are the key differences between the leading and lagging strands in DNA replication?
Leading Strand: Synthesized continuously in the 5' to 3' direction, following the replication fork. | Lagging Strand: Synthesized discontinuously in the 5' to 3' direction, away from the replication fork, forming Okazaki fragments.
Compare and contrast the functions of DNA Polymerase I and DNA Polymerase III.
DNA Polymerase III: Primarily responsible for adding nucleotides to the growing DNA strand during replication. | DNA Polymerase I: Removes RNA primers and replaces them with DNA nucleotides; also involved in proofreading.
Compare DNA replication in eukaryotes and prokaryotes.
Eukaryotes: Occurs inside the nucleus. | Prokaryotes: Occurs in the cytoplasm.
What is the difference between conservative and semiconservative replication?
Conservative: The original DNA molecule remains intact, and a completely new DNA molecule is synthesized. | Semiconservative: Each new DNA molecule consists of one original strand and one newly synthesized strand.
Differentiate between the roles of primase and ligase.
Primase: Synthesizes short RNA primers to initiate DNA synthesis. | Ligase: Seals the gaps between Okazaki fragments on the lagging strand.
What is the effect of telomere shortening?
Telomere shortening leads to the eventual cessation of cell division and contributes to aging.
What happens if Helicase is inhibited?
If Helicase is inhibited, the DNA double helix cannot unwind, preventing DNA replication.
What happens if DNA Polymerase III makes an error and it is not corrected?
If DNA Polymerase III makes an error and it is not corrected, it results in a mutation in the newly synthesized DNA strand.
What is the effect of the 5' to 3' directionality of DNA polymerase on the lagging strand?
The 5' to 3' directionality of DNA polymerase causes the lagging strand to be synthesized discontinuously in Okazaki fragments.
What is the consequence of not having single-strand binding proteins?
Without single-strand binding proteins, the separated DNA strands would re-anneal or form secondary structures, hindering replication.
What happens if ligase is non-functional?
If ligase is non-functional, Okazaki fragments on the lagging strand will not be joined, resulting in fragmented DNA.