Unit 3 - Ch 13: DNA Replication Flashcards
What is the purpose of DNA replication?
To make an exact copy of DNA before cell division
What are the three proposed models of DNA replication?
Conservative: originally DNA re-anneals, the new copy is completely separate
Semiconservative: each daughter has one of each
Dispersive: Mix of old and new DNA in each strand
What did the Meselson-Stahl experiment prove?
What is it?
DNA replication is semiconservative—each new molecule has one old and one new strand
isotope-labeled nitrogen (15N → 14N) in bacterial DNA
What enzyme unwinds the DNA double helix?
Helicase
What prevents overwinding (supercoiling) ahead of the replication fork?
Topoisomerase
What enzyme makes the RNA primer for DNA polymerase?
Primase
What enzyme synthesizes new DNA strands?
DNA polymerase III in prokaryotes.
What are Okazaki fragments?
Short DNA fragments on the lagging strand synthesized discontinuously.
What removes RNA primers and fills in gaps?
DNA polymerase I
What enzyme seals the DNA backbone?
Ligase
Why is the lagging strand synthesized differently?
DNA polymerase works only 5’→3’, so lagging strand is done in fragments away from the fork
What problem do eukaryotes face at chromosome ends?
Loss of DNA—telomeres shorten after each replication.
What solves telomere shortening?
Telomerase, which adds repeating sequences to the ends.
