Topic 3-2 Flashcards
what are the three main differences between eukaryotic and prokaryotic DNA?
- euk. DNA genome is much larger
- euk. DNA is associated with histones
- euk. DNA is linear rather than circular
which is faster at synthesizing DNA: eukaryotic DNA polymerase or prokaryotic DNA polymerase
prokaryotic DNA polymerase
how do eukaryotes overcome the limits of having slow DNA polymerase?
having multiple sites of origin of replication
a unit of replication consisting of DNA independently replicated starting from one origin of replication
replicon
how long is a typical replicon?
~200,000 - 300,000 base pairs in length
origins of replication in replication in eukaryotes are called:
origin-recognition complex (ORC)
during euk. DNA replication, how many times is the genome replicated?
once
what is the origin of replication in yeast called?
autonomously replicatin sequences (ARS)
during the initiation steps of euk DNA replication, the ORC attaches to each origin of replication with licensing factors to form:
MCM2-7 (minichromosome maintenance) and cofactors
MCM2-7 and cofactors at the start of DNA replication form:
active helicase
during what stage of the cycle is helicase activated and loaded onto the dsDNA?
S phase
what is the difference between DNA helicase in prokaryotes and DNA helicase in eukaryotes?
in prok helicase must be loaded onto ssDNA, but in euk, DNA can be loaded onto dsDNA
- has primase activity (synthesizes an RNA primer)
- DNA synthesis activity
these are characteristics of:
DNA polymerase alpha
how long are RNA primers in euk replication?
7-12 nucleotides
synthesizes DNA on the lagging strand (euk)
DNA polymerase delta
synthesizes DNA on the leading strand (euk)
DNA polymerase epsilon
how are euk RNA-DNA primers removed?
unclear
stitches okazaki fragments together
DNA ligase
how is euk DNA replication terminated?
the replication forks of adjacent bubbles run into each other and the segments of DNA fuse
to package the enormous size of euk chromosomes into a cell nucleus, its DNA must be:
highly organized and condensed
helps to package DNA
histone proteins
the fundamental unit of chromatin (2 tuns of DNA around a histone octamer)
nucleosome
creation of nucelosomes requires:
- disruption of original nucleosomes on the parental DNA
- redistribution of preexisting histones on the new DNA
- the addition of newly synthesized histones to complete the formation of new nucleosomes
abnormalities in DNA secondary structures are recognized by the:
mismatch repair system
what is the end-replication problem in linear DNA?
if you get rid of the RNA primer at the 5’ end, there is no way of filling in the gap (no exposed 3’OH)
the ends of euk chromosomes, consisting of many repeats of a short sequence of DNA
telomeres
an enzyme that elongates the ends of euk chromosomes - reverse transcriptases
telomerase
what is reverse transcriptase activity?
synthesizing DNA using an RNA sequence
true or false: linear DNA always has an overhanging end
true
what is the main function of telomeres?
protects the DNA ends of chromosomes from degradation
binds to telomeres and prevents DNA repair mechanisms from recgonizing telomere ends as a double stranded break
shelterin
where is telomerase active?
- single celled eukaryotes
- germ cells
- early embryonic cells
- proliferatice somatic cells (like bone marrow)
where is telomerase not active?
most somatic cells
what happened to the mice that were genetically engineered without telomerase?
they showed signs of premature aging after a few generations
- autosomal recessive
- mutation in the WRN gene
- symptoms of premature aging in adolescence/ adulthood
these are characteristics of:
Werner’s syndrome
what does the WRN gene code for?
telomerase replication
what percent of cancer cells express telomerase?
90%
expression of telomerase in cancer cells allows them to:
divide indefinitely
