Genetics Lecture 2 Flashcards
Name and describe the three models of DNA replication.
Semiconservative - each dsDNA splits, and each single strand receives a new strand.
Conservative - each dsDNA splits, replicates, splits, then recombines with the original.
Dispersive - DNA is chopped, alternating fragments separate into daughter cells, gaps between are filled in.
What 3 factors are needed for DNA polymerase to begin elongating?
Template
Primer
Energy - comes from the nucleotide triphosphate
Name the sites of replication in prokaryotes.
Only one - oriC
Is replication unidirectional or bidirectional?
Bidirectional.
Describe the sequence that makes up oriC.
Has 13bp sequences repeated 3x and 9b repeated 4x.
How is a replication bubble formed in oriC?
DnaA proteins bind to the 9bp repeats, causing the 13bp repeats to unwind.
DNA helicase binds to the unwound DNA at each end, and continues unwinding.
How does the leading strand differ to the lagging strand?
Leading strand is continuous.
Lagging strand is elongated in fragments, each with a primer and a nick at the end.
Which enzyme adds a primer required for okazaki fragment elongation?
RNA primase.
How long is each okazaki fragment?
100-200bp
Is replication collectively continuous or semidiscontinuous?
Semidiscontinuous.
What ligates okazaki fragments together?
DNA ligase.
Can DNA polymerase 3 elongate with no primer?
No, must have a primer.
Which enzyme replaces the RNA primer with DNA after it is extended?
DNA polymerase 1.
Why cant DNA polymerase 1 seal the nicks in okazaki fragments?
It uses energy from NTPs. No NTPs left when it reaches the nick.
What prevents single strands from recombining when unwound?
Single strand binding proteins binding to the lagging strand.