eukaryotic cell dicision Flashcards
what loads the two helicases onto dsDNA
Cdt1
what is an A-region
a A-T rich consensus sequence
features of polymerase α
has its own primase activity so it can make its own primers
no proof-reading 3’-5’ exonuclease
why is polymerase α not processive
does not associate with PCNA
function of replication factor C (RPC)
loads PCNA onto primer/DNA for a different Pol to bind to it
role of polymerase β
involved in repair
role of polymerase γ
replicates mtDNA
role of polymerase δ
lagging strand
associates with PCNA - has proof reading
role of polymerase ε
leading strand
associates with PCNA - has proof reading
which Pols can release primers
Pol epsilon
Pol sigma
what digests flaps
RNAse H1
function of flap 1 endonuclease (FEN1)
binds PCNA and can remove any incorrect nt by cutting of a section of ssDNA/RNA
what are telomeres
multiple repeats of a single sequence
TTAGGG
the last 20-200nt at the 3’ end are made of these repeats
how can cells (cancer, embryonal etc.) bypass the Hayflick limit
telomerase is a ribonucleoprotein which contains a simple repeat of CUAAC
acts as a template for telomeric repeats
how do telomeres extend
telomerase binds and extends ssDNA
Pol α binds and adds a primer
Pol δ binds to primer and extends it
DNA ligase fills in nicks
how many copies of circular mtDNA per mitochondrion are there
2-10 copies
what synthesis the leading strand of mtDNA and what is the lagging strand
Pol γ
lagging strand are RNA okazaki fragments
what is δ replication
in bacteriophages - rolling circle mechanism
nick is created - acts as primer for Pol
goes around the circle constnatly replicating
state spontaneous sources of DNA damage
replication errors
tautomerisation
deamination
depurination
state induced sources of DNA damage
intercalating agents
base analogues
deaminating agents
alkylating agents
oxidising agents
radiation/UV
how often does replication introduce an incorrect base and how do repair systems effect the error rate
10E7
10E10
what do strand slippages cause
a frame shift
extra base added
what is a tautomeric shift
enol group on T is converted to a a hydroxyl group
causes it to bind to G instead of A
how does deamination affect G, A and C and what do they bind to
C - uracil and binds to A
A - inosine/hypoxanthine binds to C
G - xanthine binds to C (less strongly)
which deamination can’t be repaired
5-methyl-C to T
what is depurination
cleavage of a sugar-base bond
forms an abasic site
what do intercalating agents do and cause and name one
insert themselves in between bases
cause frame-shift mutations
ethidium bromide
name a base analogue and why they mutate DNA
bromouracil - T analogue
incorporated into DNA
more prone to tautomeric shifts
what are alkylating agents and name one and what can it also effect seperatly
adds an alkyl group to the nucleobase
nitrosamines/methyl bromides
can speed up depurination
what are deaminating agents and name some
remove amino groups
nitrous acid
nitrosamines
nitrates/nitrites
features of oxidising agents
superoxide ion (O2-)
H2O2
causes most mutations
many possible nucleotide alterations
how does UV light cause mutations
UV-induced dimerisation of 2 adjacent thymines
stops correct base-pairing in polymerase
how does radiation, gamma/x-rays cause mutation
break bonds and create free-radicals
ss/ds breaks
bases chemically altered
leading source of mutations
