Bio Lecture 14 Flashcards
What is semiconservative DNA replication?
The strand is split into two pieces and the daughter strand contains half of the original strand.
Where does replication start and what proteins are involved?
It starts at the origin of replication which is rich in A-T bonds. There is only one site in Prokaryotes, but multiple in eukaryotes.
Origin binding proteins bind to the spot and melt the DNA open.
What proteins expand the replication fork and hold the DNA open?
Helicase uses ATP to open the DNA and advance the fork.
SSBPs (single strand binding proteins) stabilize the single stranded DNA. They bind cooperatively, so one binding helps others to bind as well. They are not enzymes.
In what direction is DNA built?
Always in the 5’ to 3’ direction because the triphosphate group on the 5’ end is needed to make the bond to the OH group on the 3’ end.
What protein catalyzes the addition of new nucleotides to make the daughter strand?
DNA Polymerase. There are several kinds, but Pol delta is the major contributor.
What are the 3 rules for DNA polymerase function?
- Makes a copy of a single strand of DNA
- Adds bases only to a free 3’OH group
- Only goes in 5’ to 3’
What is needed before DNA polymerase can start replicating?
An RNA primer needs to be laid down by DNA primase.
What example of nucleotide analogs was given and how do they combat HIV?
ZDV and ddI are both very similar to regular nucleotides, but they lack a 3’ OH group. When the RNA in the virus is being made into DNA through reverse transcriptase, these nucleotides block the production of DNA.
How are the RNA primers removed?
RNase H removes the RNA primer from the DNA so DNA polymerase can add DNA nucleotides.
What protein fixes nics?
DNA ligase repairs the nics in the DNA by forming phosphodiester bonds in the backbone of the DNA.
Why do drugs target RNase H to fight HIV?
RNase H is used to remove the RNA from a hybrid double strand of Viral DNA that will then become a double strand of DNA. Blocking RNase H prevents the viral RNA from becoming DNA.
What protein addresses the problem of supercoiling and what are the two types?
Topoisomerase I cuts one strand and lets it unwind.
Topoisomerase II cuts both strands and lets the helix unwind.
What drugs are used as chemotherapy drugs in regard to topoisomerase?
Camptothecin: inhibits Topoisomerase I
Doxorubicin: inhibits Topoisomerase II
They bind DNA and don’t let it separate into single strand in the first place, and the prevent topoisomerases from re-sealing the nics in the DNA.
What is the purpose of telomeres?
To prevent loss and damage of DNA.
What is the ‘end replication problem’ and how is it addressed?
The problem is that you cannot put a primer on the end of the DNA, so some of the information would be lost.
Telomerase uses RNA sequences in itself to add to the parental DNA strand enough DNA for a primer to be laid down for the new strand by DNA primase. After the primer is used, it is removed but not filled in. This means part of the telomere remains single stranded.
