test 2, unnamed source
Terms in this set (21)
What does semiconservative DNA replication mean?
That each daighter DNA strand contains one strand from the parent and one that is newly synthesized.
What three observations have been made for all DNA polymerases?
(1) Incoming bases are selected by complememtary base pairing by hydrogen bodning template (2) Chain grows in a 5' to 3' direction, anti-parallel to the direction of the template strand (3) All require primer strand ro add bases to; they cannot intitate it.
What is the function of DNA polymerase I?
Proofreads DNA. (about 20 at a time before it dissociates). It is a 5' to 3' DNA polymerase but also has 5' to 3' and 3' to 5' exonuclease activity to "proof read" and "correct" mismatches. It works with DNA:DNA as well as RNA:DNA. It is responsible to replacing Okazaki RNA fragments with DNA fragments.
What is a Klenow fragment?
It is the portion of DNA polymerase I that contains the polymerase and 3' to 5' exonuclease.
What is the function of DNA polymerase III?
The chief DNA replicating enzyme for E. Coli consisting of three polypeptides. It binds single stranded DNA. The alpha subunit it the polymerase and the epsilon subunit is a 3' to 5' exonuclease for proof reading.
How does DNA polymerase III achieve such high processivity?
First involved gamma subunit transferring two beta subunits to template strand. A dimer of beat subunits forms a clamp around the template and attaches the core polymerase to it. The sliding clamp allows for high processivity.
What is the function of topoisomerase?
They change the topography of DNA molecules by cutting strands, allowing the amount of supercoiling to be adjusted, and then re-ligating the strands.
What is the functions of a helicase?
They require ATP. They catalyse the unwinding of double stranded DNA by disrupting the base-hydrogen pair bodning. Single stranded proteins (SSB) attach to the single strand to keep them apart.
In replication, which is the leading strand and which is the lagging strand?
The leading strand is the strand where replication is continous. The laggins strand is the strand where replication is discontinuous.
Where is RNA used in DNA replication? What are Okazaki fragments?
On the laggin strand, primase puts down RNA pimer. The DNA that is added to these primers are called Okazaki fragments.
What does DNA liagse do?
Okazaki fragments are joined together by DNA ligase by using ATP or NAD.
Where is E. Coli DNA replication initiated, and where is it terminated?
The origin of replication is found by a unique site with 245 particular base pairs called OriC. It ends with a termination sequence when the two forks meet. Ter (tus), a protein binds to the tau or ter site to terminate replication by contractile helicase activity.
What are the processivities of DNA Polymerase I and III?
DNA Polymerase III = processivity of about 5 million BP's...DNA Polymerase I = processicity of about 20 BP before dissociation.
Where is DNA found in eukaryotes? How is DNA packaged?
In the nucleus present in chromatin. DNA is wrapped around positively charge octamers called histones. These bundles are called nucelosomes and contain 2x: H2A, 2B, 3, and 4. Around each complex is an additional H1.
What are some contrasts between features of prokaryotic and eukaryotic DNA replication?
Versus prok., Euk: A lot more DNA, have a nucleus, replication forks move a lot slower, DNA synthesis limited to a few hours, very large amounts of DNA polymerase, multiple sites of replication.
Which DNA polymerase is believed to be responsible for leading strand synthesis and which for lagging strand synthesis in eukaryotes?
DNA Polymerase delta = leading strand synthesis...DNA Polymerase alpha = lagging strand.
What proteins are in nucleosomes, and why do they bind to DNA?
Histones are positvely charged and thus bind the negative phosphate of DNA strands. These bundles are called nucelosomes and contain 2x: H2A, 2B, 3, and 4. Around each complex is an additional H1.
What is PCNA, and what role does it play?
Proliferating Cell Nuclear Antigen also known as a cyclin. Activated DNA Polymerase delta. Forms a clamp around the template DNA strand to dramatically increase porcessivity of DNA Polymerase delta.
What is the arrangement of nucleosomes after DNA replication?
Cooperative distribution of nucleosomes after replication. New synthesized histones are associated with one daughter strand along the replication fork. The original histones are conserved and the histone octomers do not completely dissociate during replication.
How might some nucleosomes affect eukaryotic DNA replication?
Since they reamain associated with one strand of the replication fork, they may be the reason why Okazaki fragments are short and DNA polymerization is so much slower.
What is the model used to describe DNA replication in mitochondria?
Circular DNA with Heavy (most Guanine) and Light (most cytosine). Two non-adjacent origins of replication. H strand replication starts origin of L strand. H strand synthesis continues byond origin of L strand synthesis. Primers are initially used by no Okazaki fragments since one at a time continuously made.