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chromosomal loops
the DNA splits into
• Metaphase compaction:
two strands
• Protein filaments come closer
• One negative
together to form a more compact
supercoil per 40
scaffold to anchor radial loops
helix turns

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11

DNA
Replication

•

After S phase and until the middle
of prophase sister chromatids are
attached along their length
• Cohesins on the arms are
released during prophase
• At anaphase cohesins are
completely released

E Coli
• Yeast
• Starts at oriC
• ARS sequences function as start
• 3 things found @
• Rich in AT
• AT-rich
• PreRC is assembled on the ARS
sequence
• ORC
• DnaA box
• First initiator of
sequence
replication
• Promotor
• MCM helicase
sequence
• Completes DNA
• GATC
licensing
methylation sites
• Forms the two
• DnaA proteins bind to the
replication forks
DnaA box
• Helicase binds
• Causing DnaC proteins to
• Primase binds to helicase and
bind
synthesizes primers
• Causes helicase to bind
• Along with polymerase
• Causes strand separation
alpha
• DNA gyrase travels in
• DNA epsilon and delta bind
front of the helicase to
and synthesize their
relieve supercoils caused
respective strands
by unwinding
• Polymerase
• Single-strand binding
alpha/primase dissolves
proteins keep the parental
so that they can bind
strand apart
• Flap endonuclease removes
• Primase bonds to helicase
the overhang caused by DNA
and synthesizes RNA
polymerase delta
primers
• Ligase seals the gaps
• Forming a primosome • Telomerase
• DNA polymerase III binds
• Extends the OG sequence of
to the complex and starts
the telomere so that the
synthesizing the strands
primer can attach to the new
• Forming a replisome
strand and synthesize a bit of
• DNA polymerase I
the new telomere
removes the RNA primers
and replaces them w DNA
• Ligase catalyzes a
covalent bond btwn
adjacent Okazaki
fragments

Opposite the oriC is a pair
of termination sequences
(ter)
• Protein known as
termination utilization
substance (Tus) binds
to one of the ters and
stops the movement
that replication fork
• Ligase links the two
daughter strands
• Forming
catenanes
• Topoisomerase II
breaks the loops and
then rejoins them
after they’ve been
unlocked
3 steps
• 3 RNA polymerases (see above)
• Initiation
• Core promoter @ ≤ 50 bp
• Promoter region: -35
upstream of initiation site
and -10 sequence on • Initiation site is Inr @ +1
template strand
• TATA box @ ~25 bp
• Pribnow Box @ - • Allows for basal transcription
10
• PROCESS:
• Transcriptional
• TFIID binds to TATA box –
start site: +1
has TBP & TBP-associated
• Transcription factors
factors (TAFs)
• RNA polymerase
• Allows for other TFs to
catalyzes synthesis of
bind
RNA
• TFIIB binds to TFIID,
• 1 RNA
promotes binding of RNA
polymerase
polymerase II to core promoter
holoenzyme
• TFIIF is bound to RNA
• 5 subunits in
polymerase II
core enzyme
• TFIIE & TFIIH bind to RNA
(a ,ß,ß’ù)
polymerase II to make the
• ß & ß’
preinitiation (closed) complex
subunit
• TFIIH acts as a helicase, forms
s do
open complex
RNA
• Phosphorylates CTD of
catalysi
RNA poly II
s
• Breaks contact btwn
• ù
TFIIB and RNA
assembl
poly II
es the
•

12 Transcriptio •
n

2

•

•

core
• Releases TFIIB,
enzyme
TFIIE, and TFIIH
• + sigma
• END: Open complex of RNA poly
factor
II & TFIIF starting to transcribe
...

es RNA RNA poly II proceeds to elongation
polyme • Promoter proximal sequence
rase on
• Btwn -50 & -200 bp
promot
• Binds activators that regulate
ers
the efficiency of initiation
• Binding of the
• Mediator:
holoenzyme
• Large protein complex,
forms a closed
manages interaction btwn
complex
activators & RNA polymerase
• At -10 seq,
• Cis-acting elements:
unwinding occurs,
• Enhancers bind activators
9-10nt RNA
• Silencer elements bind
strand made,
repressors
sigma factor
• Chromatin remodeling and histonereleased open
modifying proteins
complex
• Elongation
• The DNA must • Mostly the s

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