DNA replication Flashcards
What are the (6) enzymes required for DNA replication?
Helicase, topoisomerase, single-stranded binding protein (SBBP), RNA primase, DNA polymerase, DNA ligase.
Topoisomerase
Breaks and rejoins DNA double helix to relieve twisting forces.
Helicase
Breaks H-bonds between base pairs to untwist and open up double helix.
Single-strand bind protein (SSBP)
Stabilizes separated strands to prevent reconnecting.
RNA primase
Makes RNA primer to initiate DNA synthesis by polymerase.
DNA polymerase
Adds DNA nucleotides (free-floating) onto 3’ end of the RNA primer to synthesize new strand.
In what direction does DNA polymerase go?
In 5’-3’ direction. It places nucleotides on the 3’ end of new strand.
What are mutations?
(Rare) errors in nucloetide sequences made by DNA polymerase.
How is the leading strand made? In what direction?
RNA primer is placed at 3’ end of original strand, initiating polymerase to attach complimetary nucleotides continuously toward the replication fork.
How is the lagging strand made? In what direction? What does this result in?
- RNA primer is placed near replication fork, initiating polymerase to attach complimetary nucleotides discontinuously away from the replication fork.
- This results in Okazaki fragments, which are separated by RNA primers.
How are primers removed and Okazaki fragments joined together? Which enzymes are involved?
- Polymerase (1?) removes primers and fills gaps with nucleotides.
- DNA ligase forms phosphodiester bonds between adjacent fragments, resulting in a continuous lagging strand.
How do telomeres come about?
see appl. q
- DNA polymerase can’t add nucleotides to the 5’ tip? of the new strand bc there are no primers.
- Results in left-over single-stranded telomere.
How do DNA ends shorten over time? What does this result in?
- Telomere is cut.
- Cells can only divide a limited # of times.
What does telomerase do? Where is it active in the human body?
- Telomerase synthesizes telomere DNA, preventing chromosome shortening.
- Stem cells.
