BC368
Biochemistry of the Cell II
CARBOHYDRATE
BIOSYNTHESIS
April 14, 2015
Question 4. See pages
786-787.
Vesicles soaked in
pH 4 medium.
Chloroplast vesicles
isolated in some kind
of physiological
buffer.
vs. HCl
Effect of proton
ionophore?
Effect of DCMU?
Effect of dark?
“MY PHILODENDRON ISN’T DOING SO
WELL.”
An older philodendron is brought into the nursery in
very bad condition. It is seriously etiolated and has not
grown well for three months. Although the owner moved to
Eastern Pennsylvania from Iowa five months earlier, light
levels, humidity, and temperature are essentially similar.
You are working at the nursery to help earn extra money
while attending graduate school in biochemistry and
conduct several tests on the plant leaves to further assess
the condition of the plant:
Starch levels
Rubisco activity
Mg2+ levels
Stromal NADPH levels
Very low
Below normal in vivo levels
About normal
Slightly higher than normal
A) With this information in hand, what questions would you ask the owner?
B) In light of the answers you receive, what other tests would you do?
C) What would you recommend for treatment?
ANABOLISM VS. CATABOLISM

Anabolic and catabolic pathways share many of
the same reactions, but irreversible reactions are
bypassed.
ANABOLISM VS. CATABOLISM




Anabolic and catabolic pathways share many of
the same reactions, but irreversible reactions are
bypassed.
Anabolic and catabolic pathways undergo
coordinate control.
ATP hydrolysis drives biosynthetic processes
even when precursor concentrations are low.
Example of anabolic pathway = gluconeogenesis,
the synthesis of glucose from non-carbohydrate
precursors, which helps to maintain glucose
homeostasis.
GLUCONEOGENESIS
Red blood cells

One of the two
pathways by
which the liver
maintains
blood sugar
during times of
fasting.
Lactate
Glucose Homeostasis

Normally, blood sugar is kept fairly constant by
the liver.
Blood sugar rises after
food consumption
(postprandial period)
Glucose Homeostasis

First line of defense against a fall in blood sugar
is glycogen breakdown.
Glycogen stores
are depleted after
an overnight fast
Glucose Homeostasis

Gluconeogenesis becomes significant after about
10 hours of fasting (or during exercise to process
lactate).
Glucose Homeostasis

Hypoglycemia can result from fasting coupled
with hard work.
~Fig 14-16


Anything that
can undergo
net conversion
to
oxaloacetate
can result in
glucose.
Note that acetylCoA does NOT
result in glucose.
Central role of oxaloacetate in gluconeogenesis
Glycerol
Lactic acid
ΔG = -16 kJ/mol
Fig 14-17
Gluconeogenesis
vs.
glycolysis
ΔG = -70 kJ/mol
Fig 14-17
Bypass #1
Fig 14-18
Acetyl-CoA is a
positive effector
Pyruvate carboxylase rxn
Transport as malate
No transporter for
oxaloacetate, so it is
converted to malate for
transport to cytosol.
Enzyme is malate
dehydrogenase.
Reverse reaction in
cytosol to regenerate OA,
also producing NADH.
Fig 14-18
PEP carboxykinase rxn
Bypass II: FBPase-1 rxn
Bypass III: glucose 6 phosphatase rxn
Lactate entry
Gerty & Carl Cori
Lactate entry
Gerty & Carl Cori
Lactate entry
Lactate entry requires a
relatively high NAD+/NADH
ratio in the cytosol.
No need to go through
malate because reducing
equivalents are formed in
cytosol by LDH.
Case Study
Peter agrees to run a half marathon
with his friend from the cross country
team. He is undertrained for the race,
and his legs feel quite tired and heavy
when he is done. Afterwards, his
friend suggests that they go out for a
few beers before heading back to
campus. What does Peter tell him?
(OA)
(OA)
(OA)

Some animals are highly
dependent on gluconeogenesis.

Some animals are highly
dependent on gluconeogenesis.
Reciprocal Regulation
Regulation of pyruvate carboxylase
Acetyl-CoA acts in a
reciprocal manner on
pyruvate carboxylase
and pyruvate
dehydrogenase
complex.
High acetyl-CoA
stimulates
gluconeogenesis,
although it is not used
directly in the process.
Fig 15-22
FBPase-1/PFK-1 reciprical control
Fig 15-18
Fig 15-18
Regulation by F26BP
F26BP stimulates PFK-1
F26BP inhibits FBPase-1
Origin of F26BP
Single protein with two domains.
Activity of PFK-2/FBPase-2
is under complex hormonal
control
Fig 15-19
Regulation of [F26BP]
Case Study
You are a first-year resident called to the post-anesthesia care unit by a
nurse who is concerned about a patient she just received from the
operating room. The anesthesiologists and surgeons are all busy in the
operating rooms due to the recent arrival of multiple trauma patients, so
you need to deal with this problem on your own.
The nurse tells you that shortly after arriving in the post-anesthesia care
unit, the patient's blood pressure and heart rate began to rise. His
temperature is also rising and is currently 40°C. According to the most
recent arterial blood gas reading, the patient is acidotic with elevated
CO2.
Because you are stumped by these symptoms, the nurse gently informs
you that she believes the patient may have malignant hyperthermia, a
life-threatening syndrome that occurs during or immediately after general
anesthesia.
Along with considering how to treat the condition, you wonder what
caused the condition to develop. What is the origin of the patient’s
increased body temperature?
Malignant Hyperthermia
Malignant hyperthermia is genetic disorder that causes a rapid increase in
body temperature and muscle rigidity when the patient is given general
anesthesia.
Symptoms result from a hypercatabolic state because of a mutation in a
calcium channel of muscle. The channel opens when bound by certain
anesthetics, causing an influx of Ca2+.
Heat results from the following reactions.
PFK-1
FBPase-1
In-Class Problem
Consider a substrate cycle operating with enzymes X and Y in this pathway:
X
A
B
C
D
Y
a) Under intracellular conditions, the activity of enzyme X is 100
pmol/106 cells/s and that of enzyme Y is 90 pmol/106 cells/s. What
are the direction and rate of metabolic flux between B and C?
b) Calculate the effect of metabolic flux rate and direction after each of
the following:
i) Adding an activator that increases the activity of X by 20%
ii) Adding an inhibitor that decreases the activity of Y by 20%
iii) Adding both the activator and the inhibitor
Central role of glucose-6-P
in metabolism
Gluconeogenesis
Glucose
Glycogen synthesis overview
Glucose-6-phosphate
phosphoglucomutase
UDP-glucose
pyrophosphorylase
Step 1: phosphoglucomutase
Step 2: UDP-glucose pyrophosphorylase
Activated glucose donor
UDP-glucose
 Sugar nucleotides
are quite common
as “activated”
monosaccharides
primed for further
reaction
Fig 15-29
UDP-glucose
Step 3: Glycogen synthase
Branching enzyme
Fig 15-33
Glycogenin
Fig 15-33
Glycogenin
Regulation via
phosphorylation
Phosphorylation inactivates glycogen synthase.
Regulation via
phosphorylation
Dephosphorylation activates glycogen synthase.
Regulation via
phosphorylation
Insulin inactivates glycogen synthase kinase,
activating glycogen synthase.
Fig 15-39
Role of insulin
Regulation via
phosphorylation
Insulin activates
protein phosphatase 1
(PP1), turning on
glycogen synthase.
Glucagon and
epinephrine inactivate
protein phosphatase 1
(PP1), turning off
glycogen synthase.
Fig 15-41
Hormone
effects