8.2 Flashcards
What is the leading strand?
The strand of DNA that is synthesized continuously in the same direction as the replication fork opens.
It is synthesized towards the replication fork.
What is the lagging strand?
The strand of DNA that is synthesized discontinuously in short sections away from the replication fork.
It is synthesized in fragments known as Okazaki fragments.
What does semi-discontinuous mean?
A term describing the replication process where one strand is synthesized continuously and the other is synthesized in short segments.
This applies to the leading and lagging strands.
What is semiconservative replication?
A model of DNA replication in which each new DNA molecule consists of one old strand and one new strand.
This was demonstrated by the Meselson and Stahl experiment.
What are Okazaki fragments?
Short segments of DNA synthesized on the lagging strand during DNA replication.
They are later joined together by DNA ligase.
What are the functions of DNA enzymes?
They are responsible for various tasks during DNA replication, including unwinding the DNA and synthesizing new strands.
Key enzymes include helicase, DNA polymerases, ligase, and primase.
What is the role of helicase in DNA replication?
To unwind the DNA double helix at the replication fork.
This allows the strands to be accessible for replication.
What is the function of DNA Polymerase I?
To remove RNA primers and replace them with DNA nucleotides.
It also has proofreading capabilities.
What is the function of DNA Polymerase III?
To synthesize new DNA strands by adding nucleotides to the growing chain.
It is the main enzyme for DNA synthesis.
What is the role of ligase in DNA replication?
To join Okazaki fragments together to create a continuous DNA strand.
It seals the nicks in the sugar-phosphate backbone.
What is the function of primase?
To synthesize short RNA primers that provide a starting point for DNA synthesis.
These primers are necessary for DNA polymerases to begin replication.
What is the order of events in DNA replication?
- Unwinding of the DNA by helicase
- Synthesis of RNA primers by primase
- DNA synthesis by DNA polymerases
- Joining of Okazaki fragments by ligase
This process occurs at the replication fork.
Explain Meselson and Stahl’s experimental setup.
They grew E. coli in heavy nitrogen (N-15) and then transferred it to light nitrogen (N-14) to observe DNA replication.
Their results demonstrated that DNA replication is semiconservative.
Label a replication fork diagram with the following: Leading and lagging strands.
Leading strand: Continuous synthesis towards the fork; Lagging strand: Discontinuous synthesis away from the fork.
This labeling helps visualize the direction of strand synthesis.
