30-DNA REPLICATION IN EUKARYOTES – Dr. Block Flashcards
Where is DNA found in eukaryotes? How is the DNA packaged?
In eukaryotes DNA is found within the chromatin in the nucleus of the cell. To package all this material efficiently in a small space, negative phosphate components of DNA are wrapped around positive histones to form bundles called nucleosomes. These nucleosomes are linked to H1 histone and then tied together by linker DNA to form “beads on a string”. Further coiling and supercoiling forms chromosomes.
What are some contrasts between features of prokaryotic and eukaryotic DNA replication?
Prokaryote vs Eukaryote
Replication speed Faster in Prokaryotes
Prokaryotes have a short/small DNA length/amount
Eukaryote have a long/large DNA length/amount
Prokaryotes have few # of polymerases
Eukaryotes have Many # of polymerases (~2000)
Prokaryotes have one Replication origin
Eukaryotes have Many Replication origin (~200)
Prokaryotes synthesizing Continuously
Eukaryotes synthesize only During cell cycle.
Prokaryotes have a unidirectional replication direction.
Prokaryotes Bidirectional replication direction.
Prokaryotic Okazaki fragments are 10x larger than Eukaryotic okazaki fragments.
Eukaryotes have Telomeres, where Prokaryotes don’t.
Which DNA polymerase is believed to be responsible for leading strand synthesis and which for lagging strand synthesis in eukaryotes?
The leading strand is synthesized by DNA polymerase Delta.
DNA polymerase Alpha works on the Ozaki fragments and DNA polymerase Epsilon synthesize the lagging strand after Ozaki fragments have been created.
What proteins are in nucleosomes, and why do they bind to DNA?
Nucleosomes contain positively charged proteins called histones. There are two molecules of each histone H2A, H2B, H3 and H4. The outer part of histones are bound by histone H1. DNA binds to histones to arrange it in a compact form.
What is PCNA, and what role does it play?
PCNA (Proliferating Cell Nuclear Antigen) is a cyclin that binds to and stimulates DNA polymerase delta. It clamps around the DNA template to dramatically increase processivity of DNA polymerase delta.
What is the arrangement of nucleosomes after DNA replication? How might nucleosomes affect eukaryotic DNA replication?
Nucleosomes are arranged with histones produced during DNA replication. The newly formed histones join with one daughter strand at each end of the replication fork. The original histones do not completely dissociate during replication, thus they are conserved on each new DNA. Because of their association to the strand during replication, DNA polymerization is slow in eukaryotes and Okazaki fragments are shorter.
What is the name of the model used to describe DNA replication in mitochondria?
Mitochondrial DNA is replicated by the Displacement-loop (D-Loop mechanism) replication using DNA Polymerase Gamma. It has a heavy and a light chain, each with their own non-adjacent origins of replication. First the H strand is replicated by DNA polymerase Gamma after RNA polymerase synthesizes the primer. Eventually the original H strand is displaced as a displacement loop. As the H strand is synthesized the origin for the L chain on the original strand is exposed. A primer is synthesized and a new L chain is synthesized on the original H chain.
- Asynchronous for 2 strands
- Bidirectional from different orgins
- RNA primers
- NO Okazaki Fragments.
RECOMBINANT DNA – DR. CAMPBELL
A microRNA
a) is an RNA whose role is in transcription and post transcriptional regulation of gene expression
b) encodes a small message utilizing a genetic code
c) has sequence added to it to enable linkage to an amino acid
d) refers to RNA in the small ribosomal subunit
e) refers to small RNAs in the small and large ribosomal subunit.
a) is an RNA whose role is in transcription and post transcriptional regulation of gene expression
Proliferating cell nuclear antigen affects the processivity of DNA polymerase delta by
a) performing a proofreading type of function
b) forming a clamp around the template strand
c) performing a snowplow type of editing function
d) forming a nucleosome using a histone complex
e) shortening the Okazaki fragments
b) forming a clamp around the template strand [to increase processivity of DNA polymerase Delta]
