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.
Also known as the continuous strand.
What is the lagging strand?
The strand of DNA that is synthesized discontinuously in fragments opposite to the direction of the replication fork.
Also known as the discontinuous strand.
What does semi-discontinuous mean?
Refers to the replication process where one strand is synthesized continuously (leading) and the other in short fragments (lagging).
This characteristic is crucial for DNA replication efficiency.
What is semiconservative replication?
The mechanism by which DNA is replicated, where each new double helix consists of one old strand and one newly synthesized strand.
This was demonstrated by the Meselson and Stahl experiment.
What are Okazaki fragments?
Short sequences of DNA that are synthesized on the lagging strand during DNA replication.
They are later joined together by the enzyme ligase.
What are the functions of DNA enzymes?
Enzymes that facilitate the processes of DNA replication and repair, including unwinding, polymerization, and joining of DNA strands.
Key enzymes include helicase, DNA polymerase, and ligase.
What is the function of helicase?
An enzyme that unwinds the double-stranded DNA helix at the replication fork.
This is essential for allowing access to the template strands for replication.
What is the role of DNA Polymerase I?
An enzyme involved in DNA replication that removes RNA primers and replaces them with DNA.
It also has proofreading capabilities to ensure fidelity.
What is the role of DNA Polymerase III?
The primary enzyme responsible for synthesizing new DNA strands during replication.
It adds nucleotides to the growing DNA strand in a 5’ to 3’ direction.
What is the function of ligase?
An enzyme that joins Okazaki fragments on the lagging strand by forming phosphodiester bonds.
This is crucial for creating a continuous DNA strand.
What does primase do?
An enzyme that synthesizes short RNA primers necessary for DNA polymerases to initiate DNA synthesis.
Primers provide a free 3’ hydroxyl group for nucleotide addition.
What is the order of events in DNA replication?
- Unwinding of the DNA helix by helicase
- Synthesis of RNA primers by primase
- DNA synthesis by DNA polymerase
- Joining of fragments by ligase
This sequence ensures accurate and efficient replication.
Explain Meselson and Stahl’s experimental setup.
They used isotopes of nitrogen to label DNA in bacteria, allowing them to track the distribution of old and new strands after replication.
Their results confirmed the semiconservative model of DNA replication.
Label a replication fork diagram with leading and lagging strands.
Leading strand on the side where replication is continuous and the lagging strand on the opposite side where replication occurs in fragments.
Include 3’ and 5’ ends and Okazaki fragments in the diagram.
