Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
16 Cards in this Set
- Front
- Back
|
What was the mechanism that Watson & Crick sought out to explain? |
That because two strands in DNA are complementary to each other, each could serve as a template for a new strand. They proposed that strands separate and the new strands are built off of these. |
|
|
They proposed 3 models to potentially explain their theory. What were the 3 models? |
Dispersive Semi-conservative Conservative |
|
|
Dispersive |
The parental strand is separated into segments and each new strand consists in parts of both parental and new DNA. |
|
|
Semi-Conservative |
Each strand is serving as a template and the new double strand contains one parental and one new strand |
|
|
Conservative |
A double stranded copy is generated and the parental DNA is conserved as a double strand |
|
|
How can you distinguish between the original strands of DNA & the newly synthesized strands? |
We separate DNA molecules by size in a column by using CsCl equilibrium centrifugation. This is a viscous substance that when you add DNA to it, you can separate it by its density. The DNA will migrate within the CsCl gradient to wherever its density matches that CsCl gradient. We get the DNA to migrate by using centrifugation. |
|
|
Explain the process of CsCl equilibrium centrifugation |
They created DNA with a higher density by incubating bacteria in an isotope of Nitrogen that is more dense. They grew the bacterial cells in the source of Nitrogen so that all the DNA that it's making and replicating contains the heavy Nitrogen. Then, we can expose this heavy DNA to the light DNA and see how it gets incorporated. So they isolated DNA from the heavy label, centrifuged it for 2 days in the CsCl gradient and then looked at the location when the DNA is in the tube. |
|
|
We allow DNA to replicate in a first round in heavy or light DNA? |
We isolate the heavy DNA and expose it to light DNA, so every new strand that gets incorporated will be light. |
|
|
After one round of DNA replication, what experimental result do you expect for the dispersive model? |
We expect them to be all mixed. Each molecule will have amounts of heavy DNA and light DNA on each strand. |
|
|
After one round of DNA replication, what experimental result do you expect for the semi-conservative model? |
The strands separate and we build a new complementary strand with the light DNA. They will be all mixed because one strand will be heavy and the other strand will be light. We get the same result in Dispersive but by a different mode. |
|
|
After one round of DNA replication, what experimental result do you expect for the conservative model? |
We will get half heavy and half light. One full molecule will be heavy and the other will be full light. |
|
|
What was the actual result from round 1, and what can we now exclude? |
The result was that we'd get all mixed, so we can exclude the conservative model now. |
|
|
After a second round of DNA replication, what experimental result do you expect for each the dispersive model? |
They would all be mixed and lighter. Any new DNA that is synthesized is now light. |
|
|
After a second round of DNA replication, what experimental result do you expect for each the semi-conservative model? |
They will be mixed and light. |
|
|
What was the actual result from the second round? |
They turned out to be all mixed and light. |
|
|
Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? |
If you grow a bacteria in a radioactive thymine when it replicates its DNA all of that DNA will have radioactive thymine in it. So when it divides, both of the daughter cells will contain that radioactive thymine. If you switched back and had regular thymine then you could reduce radioactivity with each subsequent division. |
