8.2 Study Guide Flashcards
What is the leading strand?
The leading strand is the DNA strand that is made continuously. The new nucleotides tides are added in the direction of replication (towards the Helicase).
What is the lagging strand?
The lagging strand is the strand of DNA that is made discontinuously into short fragments. The nucleotides are added away from the direction of replication (away from the Helicase).
What is a semi-discontinuous process?
A process where some parts are continuous, while other parts are not. For example, in DNA replication, the leading strand is continuously synthesized, while the lagging strand is synthesize discontinuously into short fragments.
What is semi-conservative replication?
Semi-conservative replication takes place when the new template for the new strand of DNA is different than that of the original parent strand. This creates a hybrid strand of DNA.
What are Okazaki fragments?
The fragments of DNA on the lagging strand.
What are the DNA enzymes and what are their functions?
Helicase: Unzips the DNA at the beginning of replication
Primase: Adds RNA Primers to the separated DNA strands
DNA Polymerase III: Adds new DNA nucleotides to build complementary strands
DNA Polymerase I: Removes RNA Primers and replaces them with DNA nucleotides
Ligase: Joins the fragments of DNA that have been built separately
What is the order of events in DNA replication?
Start
1.Unzip and unwind the DNA
2. Add RNA primers
3. Add new nucleotides to build a new complementary strand
4. Replace RNA primers with DNA nucleotides
5. Join remaining fragments together to make the strand continuous
Two identical molecules of DNA are made
Explain Meselson and Stahl’s experimental setup and what was concluded from the results.
Meselson and Stahl grew E. coli in a heavy nitrogen environment, then switched it to a lighter nitrogen environment. Then, they spun the E. coli in an ultracentrifuge and the heavy nitrogen sunk to the bottom of the tube, while the lighter nitrogen moved towards the top of the tube. When the DNA strands are copied, the scientists spun the new strands in the ultracentrifuge to see how many of each nitrogen there were. The heavy nitrogens sunk to the bottom of the tube, the hybrid nitrogens stay in the middle, and the lighter nitrogens rose to the top. They found that DNA becomes less dense across generations. When the DNA strands were copied N14, the lighter nitrogen, was added to make new strands. This decreased the density of each strand. They concluded that if the conservative model of DNA was correct, then the strands would either be 100% heavy nitrogen or 100% light nitrogen. If the dispersive model of DNA was correct, all of the nitrogens would be hybrid strands.
