week 4 Flashcards
BACTERIAL DNA REPLICATION: where do initiator proteins bind to?
Bind to origin (AT rich sequence), requires ATP, they denature the sequence a little
BACTERIAL DNA REPLICATION: what do initiator proteins do?
help helicase bind
BACTERIAL DNA REPLICATION: how many types of helicase exist?
two
BACTERIAL DNA REPLICATION: in which direction does the predominant helicase move?
5’-3’ along the LAGGING strand template
BACTERIAL DNA REPLICATION: does helicase require atp?
yes
BACTERIAL DNA REPLICATION: how many subunits does helicase have
6 (has quaternary structure)
BACTERIAL DNA REPLICATION: what do single-strand binding proteins do?
- separate DNA strands by binding ssDNA
- Prevents strands from H-bonding (also prevents hair pins or loops—H-bonding w/n a strand—until replication can occur
BACTERIAL DNA REPLICATION: What does DnA polymerase require in order to begin?
A bound primer (~10 nucleotides long, with a free 3’ OH bp to the template)
BACTERIAL DNA REPLICATION: what is the purpose of primase?
synthesize an RNA primer
BACTERIAL DNA REPLICATION: What direction does primase proceed in?
reads 3’-5’ along template strand
BACTERIAL DNA REPLICATION: why is DNApol used at all?
cell doesn’t like to have duplexes very long (RNA and DNA bound), DNApol is very efficient and quick but just can’t start w/o primer which can start a new sequence just from template and raw materials
BACTERIAL DNA REPLICATION: helicase + primase =
primosome
BACTERIAL DNA REPLICATION: what does the sliding clamp do?
ring shaped protein that doesn’t impede function of DNAPol but hods it on tightly enough so it won’t fall off and DNAPol doesn’t have to bind very tightly (get slowed down and needs to be able to release template strand at certain points)
BACTERIAL DNA REPLICATION: How doe the removal of RNA primers work
DNA repair system is responsible for removal of the RNA primer and replacing it with correctly matched DNA sequence, Repair polymerase uses original template DNA to guide replacement of RNA primer with DNA
BACTERIAL DNA REPLICATION: how are the Okazaki fragments on the lagging strand linked together
ligase seals the nick after RNA primers are removed and replaced w correctly match DNA sequence
NOTE: not a gap, there are no nucleotides missing
BACTERIAL DNA REPLICATION: leading strand is synthesized _________ from _______________ primer (s)
continuously, single RNA
BACTERIAL DNA REPLICATION: Lagging strand is synthesized _____________ from _____________ primer(s)
discontinuously, multiple
BACTERIAL DNA REPLICATION: Okazaki fragments:________ + ___________
RNA primer + DNA
DNA synthesis proceeds in which direction?
5’-3’
What problem does DNA topoisomerase solve?
as helicase unwinds DNA, supercoiling and torsional strain increases, this is a problem in circular chromosomes and large linear euk chromosomes
Why is the shortening of the 5’ end of the daughter DNA a potential problem? How does this problem arise?
there could be a loss of sequence information. RNA primer cannot bind to the very end
for which strand is the shortening of the 5’ end a concern?
Lagging
How does telomerase solve the problem of the shortening of the 5’ end?
telomerase binds to an RNA template and generates G-rich, repetitive sequences on the 3’ end of the parental template.
In certain circumstances cancer cells can reactivate _____________ (which is usually not abundant in somatic cells)and the cancer cells can add more _______ which help the cell to ___________ indefinitely
telomerase, telomeres, replicate
