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Bis 101
Lecture 8
| Question | Answer |
|---|---|
| What is the semi-conservative mechanism for DNA replication? | When one parental DNA splits in round one to make two DNA, half parent, half daughter, and in round two makes 4 DNA, 2 that are wholly daughter, and two that are half daughter half parent |
| What is the conservative mechanism for DNA replication? | When one parent DNA strand splits in round one to form one daughter and one parent DNA, and in round two split to form 3 daughter DNA and 1 parent DNA |
| What is the dispersive mechanism for DNA replication? | When the parent DNA splits in the first round to form 2 half and half DNA's and in the second round split again to make 4 DNA's that are mostly daughter, however spliced intermittently with parental DNA |
| What did Meselson and Stahl do to figure out which form of DNA replication was the right one? | Grew E. Coli in a medium with Nitrogen 15 isotope, then switched to medium with N 14 and collected samples after each generation. |
| What did Meselson and Stahl do after they collected the generations of E. Coli? | They put the samples through a centrifuge, then examined the samples under UV light. After examining the bands that formed they concluded that the semi-conservative model was the correct one. |
| What is the origin of replication? | The start point of replication. Prokaryotes have one, Eukaryotes have many |
| How does DNA replication begin? | At the origin of replication, the DNA splits into what is called a replication bubble. At the replication forks at either side of the bubble synthesis of new DNA begins. |
| How is the lagging strand synthesized? | Primase first synthesizes short RNA primers from DNA at the replication fork at the 5 prime end. This is then elongated by DNA polymerase 3 with new DNA. Polymerase 1 then removes the RNA at the 5 prime and fills the gaps. Ligase connects the fragments. |
| How does DNA replication spread after the replication bubble is formed? | DNA Helicase travels 5 to 3 and uses ATP to split the DNA and move the fork. DNA topoisomerase right ahead of helicase prevents additional coiling ahead of the fork. After helicase single-stand binding proteins keep the DNA strands separate. |
| What does the topoisomerase, DNA gyrase do and how? | It removes additional coils in the DNA by cutting it, rotating, and then rejoining the DNA strands together right before the splitting fork and DNA Helicase. |
| What does DNA polymerase do and how? | It runs along the DNA after being split by helicase and uses it as a template and attaches deoxynucleoside triphosphates. This makes a second strand attached to the original template. It runs 3 to 5 on the template strand and 5 to 3 on the new strand. |
| What does Primase do and why? | Primase creates a short RNA primer at the replication fork so that DNA polymerase 3 can attach to the template strand and make the new leading/lagging strand. In the leading strand it makes one RNA primer, in the lagging strand it makes several. |
| How are primers removed? | As the DNA polymerase runs along the lagging strand, it eventually runs over the primers and replaces the RNA with DNA |
| What does DNA ligase do and why? | The DNA ligase joins the okazaki fragments. This occurs after the polymerase runs over the RNA primers and converts then into DNA |
| What are the three reasons that DNA replication is so accurate? | 1: The hydrogen bonds between A and T and G and C are more stable than mismatches. 2: DNA polymerase is unlikely to form bonds on mismatches. 3: DNA polymerase and other enzymes proof read the DNA |
| Why do eukaryotes have telomeres? Why don't prokaryotes? | Eukaryotes need telomeres because without them DNA replication could not finish on the lagging strand because there is no place to attach a primer upstream. Prokaryotes have linear DNA so there is no end. |
| What are telomeres? | These are a series of repeated sequences within the DNA at the 3 end. This series does not have a complementary strand and acts as an overhang on the DNA. This gives a place for RNA primers to attach. |
| What does telomerase do? | Telomerase creates the telomers at the 3 end using dNTPs. The DNA builds on this RNA making the overhang large enough so that a complementary primer can be attached. |
Created by:
24rory
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