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Questions and Answers
What is the name of the enzyme that joins the Okazaki fragments?
What is the name of the enzyme that joins the Okazaki fragments?
- DNA polymerase III
- DNA ligase (correct)
- DNA polymerase I
- Primase
What is the problem with replicating the lagging strand at the end of a linear chromosome?
What is the problem with replicating the lagging strand at the end of a linear chromosome?
- The replisome cannot coordinate the replication
- The Okazaki fragments are not synthesized correctly
- The leading strand cannot reach the end
- DNA polymerase cannot add to the end without a primer (correct)
What is the term for the region at the end of a eukaryotic chromosome?
What is the term for the region at the end of a eukaryotic chromosome?
- Chromatin
- Telomere (correct)
- Replisome
- Centromere
How are the leading and lagging strands replicated in relation to each other?
How are the leading and lagging strands replicated in relation to each other?
What is the role of DNA polymerase I in lagging strand synthesis?
What is the role of DNA polymerase I in lagging strand synthesis?
What is the purpose of the RNA primer in lagging strand synthesis?
What is the purpose of the RNA primer in lagging strand synthesis?
What is the direction of DNA synthesis catalyzed by DNA polymerase?
What is the direction of DNA synthesis catalyzed by DNA polymerase?
What provides the energy input for polymerizing DNA?
What provides the energy input for polymerizing DNA?
How many replication bubbles are formed in bacterial cells during DNA replication?
How many replication bubbles are formed in bacterial cells during DNA replication?
What is the direction of movement of the replication forks during DNA replication?
What is the direction of movement of the replication forks during DNA replication?
How do eukaryotic cells differ from bacterial cells in terms of replication bubbles?
How do eukaryotic cells differ from bacterial cells in terms of replication bubbles?
What is the role of DNA polymerase in DNA synthesis?
What is the role of DNA polymerase in DNA synthesis?
What is the primary function of DNA helicase during DNA replication?
What is the primary function of DNA helicase during DNA replication?
What is the role of single-strand DNA-binding proteins (SSBPs) during DNA replication?
What is the role of single-strand DNA-binding proteins (SSBPs) during DNA replication?
What is the direction of synthesis for DNA polymerase?
What is the direction of synthesis for DNA polymerase?
What is the limitation of DNA polymerase in terms of starting synthesis?
What is the limitation of DNA polymerase in terms of starting synthesis?
What is the result of 5' → 3' synthesis on the two strands of DNA?
What is the result of 5' → 3' synthesis on the two strands of DNA?
What is the purpose of Topoisomerase during DNA replication?
What is the purpose of Topoisomerase during DNA replication?
What is the consequence of single-stranded DNA being left at the end of the lagging strand during replication?
What is the consequence of single-stranded DNA being left at the end of the lagging strand during replication?
What is the primary function of telomerase?
What is the primary function of telomerase?
What is the purpose of the single-stranded 'overhang' formed during telomere replication?
What is the purpose of the single-stranded 'overhang' formed during telomere replication?
What is the consequence of telomere shortening during replication?
What is the consequence of telomere shortening during replication?
Where is telomerase primarily found?
Where is telomerase primarily found?
What is the end replication problem?
What is the end replication problem?
What is the role of primase in DNA synthesis?
What is the role of primase in DNA synthesis?
In which direction is the leading strand synthesized?
In which direction is the leading strand synthesized?
What is the name of the process by which the lagging strand is synthesized?
What is the name of the process by which the lagging strand is synthesized?
What is the function of DNA polymerase in leading strand synthesis?
What is the function of DNA polymerase in leading strand synthesis?
What is the problem faced during telomere replication?
What is the problem faced during telomere replication?
What is the replisome responsible for?
What is the replisome responsible for?
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Study Notes
The End Replication Problem
- Single-stranded DNA is left at the end of the lagging strand during replication
- This single-stranded DNA is eventually degraded, which would shorten the chromosome by 50 to 100 nucleotides each time replication occurs
- Over time, linear chromosomes would vanish if not for the solution of telomeres
Telomeres and Telomerase
- Telomeres are regions at the end of eukaryotic chromosomes that do not contain genes
- Consist of short, repeating stretches of bases
- Telomerase solves the end replication problem by replicating telomeres using an RNA template
- Telomerase adds short DNA sequences to the end of the parent strand, preventing the shortening of telomeres
Effect of Telomere Length on Cell Division
- Telomerase is primarily found in gametes and stem cells, as well as in cancer cells
- Telomere length affects cell division, with shorter telomeres limiting the number of cell divisions
Lagging Strand Synthesis
- The lagging strand is synthesized as short, discontinuous fragments called Okazaki fragments
- DNA polymerase I removes the RNA primers and replaces them with DNA
- The enzyme DNA ligase joins the Okazaki fragments, making the lagging strand intact
DNA Replication
- DNA replication occurs in a 5' → 3' direction
- The leading strand is synthesized continuously in the 5' → 3' direction
- The lagging strand is synthesized discontinuously in the 5' → 3' direction
- Replication bubbles form at specific sequences, known as origins of replication, and grow in two directions
- The replisome is a large grouping of enzymes that coordinates DNA replication
Enzymes Involved in DNA Replication
- Helicase: separates the two strands of DNA
- Single-Strand Binding Proteins: holds separated single strands apart
- Topoisomerase: relieves tension on the DNA molecule ahead of the fork
- RNA primase: synthesizes a short piece of RNA (the primer)
- DNA polymerase III: adds nucleotides to the primer
- DNA polymerase I: a repair enzyme that removes the RNA primer
- DNA ligase: repairs the sugar-phosphate backbone
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