PL1 Flashcards
When is information stored in DNA copied (replicated)
Whenever a cell divides
What is the difference between transcription and replication in terms of DNA polymerase and RNA polymerase
DNA pol can’t start a strand from scratch (only elongate whereas RNA polymerase can
What strand of the double helix, once denatured, is used as a template for daughter strand
Both
What is the relationship between the daughter strand and the template strand of DNA
Daughter is complementary to parental strand
What does the alpha (first) phosphate group in the dNTP react with and what kind of bond is it
3’ hydroxyl group in the growing DNA chain
High energy bond
What does DNA helicase do
Unwinds the duplex DNA for access
What does DNA topoisomerase do
Relieves the supercoils after unwinding
Which strand is the leading strand
5’ to 3’ (3’ end) so DNA is synthesized 5’ to 3’ in direction of replication fork
Which strand is the lagging strand
3’ to 5’ end
Which way does DNA synthesis always proceed
5’ to 3’
Why is a primer necessary in DNA replication
DNA polymerases can’t initiate synthesis of a new strand, they can only elongate an existing strand
What is primase
A specialized RNA polymerase
What does primase do in replication
Forms a short RNA molecule complementary to a single-stranded region of the denatured and unwound duplex DNA
What does DNA polymerase do in replication
Extends the primer to eventually form a new daughter duplex DNA
Why does synthesis only occur in 5’ to 3’
Because you need a 3’ hydroxyl group to add the next nucleotide
What is the relationship between the two strands on duplex DNA
They are antiparallel
What are Okazaki fragments and where are they found
Short discontinuous fragments consisting of RNA and DNA found on the lagging strand
How do the Okazaki turn from fragments to a daughter strand
The RNA components of the Okazaki fragments are replaced by DNA and the two adjoining DNA molecules are ligated together
What ligates the Okazaki fragments
DNA ligase
What is much of what we know about DNA replication obtained from
Studies using prokaryotes, viruses and from budding yeast
What is the large t-antigen and what does it do
It’s a hexamer, helicase encoded by the viral genome and unwinds the double helix at the replication fork
What does replication protein A do
- Binds single-stranded DNA
- Keeps single-stranded DNA in optimal conformation for DNA polymerase
- Increases accuracy of reaction
What does DNA polymerase epsilon do
Carries out leading strand DNA synthesis
What is PCNA and what does it do
Homotrimetric protein
Prevents polymerase epsilon complex from disassociating from the template
