diauxic_pre-class

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Unformatted text preview: The
diauxic
growth
curve
–
Homework
assignment
 
 
 Next
 session
we
will
try
to
reproduce
the
famous
diauxic
growth
 curve
 experiment
 first
 performed
by
 Jacques
 Monod
in
the
1940’s
during
his
PhD
work.
 Subsequent
work
by
 Monod
led
him
 to
decipher
the
basic
mechanisms
of
gene
regulation
and
propose
the
 lac
 operon
 model
 of
 gene
 expression,
 for
 which
 he
 received
 the
 Nobel
 prize
 together
 with
 Jacob
 and
 Lwoff
in
1965.
The
idea
behind
the
 diauxic
growth
experiment
 (literally
 meaning
double
growth)
 is
very
simple
 –
we
put
E.
coli
in
a
medium
with
two
types
of
 sugars,
 one
 that
 it
 can
 directly
 metabolize
 (for
 example
 glucose)
 and
 a
 second
 sugar
 (lactose
for
example)
 that
needs
to
be
further
processed
in
order
to
be
metabolized
by
 the
cell.
What
Monod
discovered
was
that
 the
cell
prefers
to
 first
 digest
glucose,
which
 endows
the
cell
with
a
higher
growth
rate
(making
it
more
fit),
and
only
when
glucose
is
 exhausted
 from
 the
 medium
 will
 it
 start
 to
 synthesize
 the
 machinery
 needed
 to
 transport
and
digest
and
ultimately
grow,
albeit
more
slowly,
on
 the
second
sugar.
Thus
 growth
on
a
mixture
of
sugars
 therefore
 exhibits
the
following
phases:
(1)
fast
growth
 on
 glucose
 (2)
 lag
 period
 (3)
 slower
 growth
 on
 lactose
 (4)
 saturation.
 See
 for
 example
 Fig.
1d
taken
from
Monod’s
Nobel
lecture.

The
following
is
Monod’s
own
account
of
his
 findings.
 
 lag 
 
 
 
 1 
 
 
 “I
was
working
then
at
the
old
Sorbonne,
in
an
ancient
laboratory
that
opened
 on
a
gallery
full
of
stuffed
monkeys.
Demobilized
in
August
in
the
Free
 Zone
after
the
disaster
of
1940,
I
had
succeeded
in
locating
my
family
living
 in
the
Northern
Zone
and
had
resumed
my
work
with
desperate
eagerness.
I
 interrupted
work
from
time
to
time
only
to
help
circulate
the
first
clandestine
 tracts.
I
wanted
to
complete
as
quickly
as
possible
my
doctoral
dissertation,
 which,
under
the
strongly
biometric
influence
of
Georges
Teissier,
I
had
devoted
 to
the
study
of
the
kinetics
of
bacterial
growth.
Having
determined
the
 constants
of
growth
in
the
presence
of
different
carbohydrates,
it
occurred
to
 me
that
it
would
be
interesting
to
determine
the
same
constants
in
paired
 mixtures
of
carbohydrates.
From
the
first
experiment
on,
I
noticed
that,
 whereas
the
growth
was
kinetically
normal
in
the
presence
of
certain
mixtures
 (that
is,
it
exhibited
a
single
exponential
phase),
two
complete
growth
cycles
 could
be
observed
in
other
carbohydrate
mixtures,
these
cycles
consisting
 of
two
exponential
phases
separated
by
a‐complete
cessation
of
growth
 (Fig.1).”
–
1965
Nobel
lecture
by
Monod
 
 The
 following
 is
 a
 simple
 exercise
 in
 gross
 estimation.
 Monod
 concluded
 that
 when
 glucose
is
exhausted
by
the
cell
the
diauxic
shift
occurs.
Can
you
predict
based
on
simple
 arguments
when
this
will
occur?
 
 Here
is
the
experimental
setup.
 
 At
 t=0
 you
 inoculate
 a
 1L
 growth
 medium
 containing
 0.1g/L
 of
 glucose
 with
 10mL
 of
 saturated
E.
coli
culture
(@
 1.5∙108
cells/mL)
and
allow
the
cellsto
grow
aerobically
at
 37degC.
Assume
that
the
cells
are
growing
exponentially
with
a
doubling
time
of
20
min,
 and
that
at
this
growth
rate
an
average
cell
has
about
6∙106
proteins
per
cell
(on
average
 300
aa
in
length
each).
 You
may
also
assume
that
the
medium
has
been
supplemented
 with
 amino
 acids
 so
 that
 the
 cell
 doesn’t
 need
 to
 synthesize
 these
 building
 blocks
 for
 itself.
Under
these
conditions
it
is
known
that
most
of
the
energy
consumed
by
the
cell
 is
required
for
amino
acid
polymerization
(i.e.
making
proteins).
 Finally
you
will
need
to
 know
that
under
aerobic
growth
conditions
the
cell
can
generate
30
ATP
molecules
from
 each
 glucose
 molecule,
 and
 that
 4
 of
 these
 ATP
 molecules
 are
 required
 to
 elongate
 a
 single
peptide
bond.
Hint:
estimate
the
total
number
of
glucose
molecules
in
the
medium
 and
 compare
 that
 with
 the
 number
 of
 glucose
 molecules
 being
 consumed
 by
 the
 exponentially
growing
population
of
cells.

 
 Please
 also
 read
 up
 a
 little
 on
 the
 lac
 operon
 (for
 example
 in
 Alberts,
 Essential
 cell
 biology
pp.
271‐
275
or
PBoC
pp.
138‐
140,
section
4.4.3)
 2 Some
references
 
 Diauxic
growth
 http://nobelprize.org/nobel_prizes/medicine/laureates/1965/monod‐lecture.html
 http://en.wikipedia.org/wiki/Diauxie
 http://en.wikipedia.org/wiki/Lac_operon
 http://bioinfo.bact.wisc.edu/themicrobialworld/regulation.html
 Brock,
Biology
of
microorganisms,
2006,
pp.
216‐218
 “The
Growth
of
Bacterial
Cultures”
–
Monod,
Ann
Rev
Micro
Biol
3:
371,
1949.
 “The
phenomenon
of
enzymatic
adaptation”
–
Monod,
GROWTH
11
(4):
223‐289,
1947
 
 Growth
phases
 Brock,
Biology
of
microorganisms,
2006,
pp.
142‐144
 Microbe,
Schaechter,
Ingraham
and
Neidhardt,
2006,
pp.
55‐58,
259‐262.
 
 The
lac
operon
 http://en.wikipedia.org/wiki/Lac_operon
 Microbe,
Schaechter,
Ingraham
and
Neidhardt,
2006,
pp.
229‐232.
 Little
Alberts,
pp.
271‐
275
 PBoC
pp.
138‐
140,
section
4.4.3
 
 Other:
 “Bacterial
Growth:
Constant
Obession
with
dN/dt”
–
Neidhardt,
J
Bact
181:
7405,
1999.
 
 
 
 3 ...
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This document was uploaded on 01/03/2012.

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