Honor Bio 8.2 Flashcards
What is the leading strand?
The continuously synthesized DNA strand in the 5’ to 3’ direction during replication.
What is the lagging strand?
The DNA strand synthesized discontinuously in short fragments (Okazaki fragments) in the 5’ to 3’ direction.
What does “semi-discontinuous” mean in DNA replication?
One strand (leading) is synthesized continuously, while the other (lagging) is synthesized in fragments.
What does “semiconservative replication” mean?
Each daughter DNA molecule consists of one original (parental) strand and one newly synthesized strand.
What are Okazaki fragments?
Short DNA fragments synthesized on the lagging strand during replication.
What is the function of helicase?
Unwinds the DNA double helix by breaking hydrogen bonds between base pairs.
What is the function of DNA Polymerase I?
Removes RNA primers and replaces them with DNA nucleotides.
What is the function of DNA Polymerase III?
Synthesizes the new DNA strand by adding nucleotides in the 5’ to 3’ direction.
What is the function of ligase?
Joins Okazaki fragments by sealing gaps in the sugar-phosphate backbone.
What is the function of primase?
Synthesizes short RNA primers to provide a starting point for DNA polymerase.
List the key steps in DNA replication in order.
Helicase unwinds the DNA helix.
Primase synthesizes RNA primers.
DNA Polymerase III synthesizes the leading strand continuously.
DNA Polymerase III synthesizes the lagging strand in Okazaki fragments.
DNA Polymerase I removes RNA primers and replaces them with DNA.
Ligase seals the gaps between Okazaki fragments.
Explain Meselson and Stahl’s experimental setup and what they concluded.
They grew E. coli in a medium with heavy nitrogen so that all DNA contained heavy nitrogen.
Then, they transferred bacteria to a medium with lighter nitrogen.
After one round of replication, DNA was an intermediate weight, ruling out conservative replication.
After two rounds, they saw both intermediate and light DNA, confirming semiconservative replication: each new DNA molecule contains one old and one new strand.
