Pentose Phosphate Shunt Flashcards
where are the enzymes for the pentose phosphate shunt found
in the cytosol
important products of the pentose phosphate shunt?
NADPH and ribose-5-phosphate (R5P)
The first three steps are referred to as the ___ phase
oxidative
oxidative phase
G6P is converted to what? what is released
G6P converted to Ru5_
Co2 is released
what is formed during the oxidative phase per glucose
6 NADPH are formed
3 co2 is released
3 Ru5P
enzymes invovled in the oxidative phase (G6P–>Ru5P)
two dehydrogenases and lactose
phase after the oxidaitive phase?
nonoxidative phase
nonoxidative phase
converts Ru5P to
intermediates of the glycolytic pathway
Ru5P → 2 F6P + 1 GAP
isomerase, epimerase, transketolase, and transaldolase
are all invovled in
non oxidative phase
Ru5P → 2 F6P + 1 GAP
nonoxidative phase
the enzyme ___ has TPP as a prosthetic group for transferring C2 groups
transketolase
how many Co2 does the oxidative phase yeild?
3
glucose has 18 carbons = three CO2 (3 carbons), three Ru5P (15 carbons), and six NADPH
how many Ru5P does the oxidative phase yeidl?
3 Ru5P
glucose has 18 carbons = three CO2 (3 carbons), three Ru5P (15 carbons), and six NADPH
how many nadph does the oxidative phase yield?
6 nadph
glucose has 18 carbons = three CO2 (3 carbons), three Ru5P (15 carbons), and six NADPH
In the nonoxidative phase, we use the three Ru5P to make___ before F6P and GAP
one R5P and two Xu5P
one R5P and two Xu5P from the 3 Ru5P are used to make
two F6P and one GAP
from phosphate shunt, you gain 6 nadph at the expense of
one GAP → three CO2
___ is used primarily as a reductant,
NADPH
NAD+ is used primarily as an ___
oxidant
which tissues have pentose phopshate pathways?
The main uses of NADPH are in ___ and ___
biosynthesis and detoxification
**_NADPH_** is used by **_cytochrome P450_** in the small intestine (and liver) to detoxify \_\_\_\_
xenobiotics
In red blood cells, NADPH is needed to detoxify
reactive oxygen species (ROS)
Most common human enzyme deficiency is
G6PDH Deficiency
consequences of G6PDH Deficiency
Favism (Hemolytic anemia) when they take antimalralial drugs (quinine or chloroquine)
Selective advantage where malaria is endemic
why does G6PDH Deficiency have an advantage with malaria?
it’s better to pay the metabolic cost of a faster rate of turnover of RBC’s than to die from malaria
If we need ribose but not NADPH, we can
un the nonoxidative phase of the Shunt in reverse, starting with F6P and GAP and ending with R5P
If we need ribose but not NADPH, what do you start with?
starting with F6P and GAP and ending with R5P
what do we need ribose for?
information storage, energy transfer, oxidation/reduction reactions, and enzyme catalysis
how does the body get both nadph and ribose from the shunt?
run just the oxidative phase of the Shunt and convert all of the Ru5P produced to R5P
Any ratio other than 2 nadph/ribose can be obtained by
running the oxidative phase in the forward direction and the nonoxidative phase in either direction.
In liver, up to ____% of the Glu metabolized goes through the pentose phosphate shunt
30
• G6Pase is only present in
liver and to a small extent in kidney
Glu is the primary fuel in (2)
brain and RBC
During ____, liver uses its glycogen to maintain blood Glu
fasting
Glucose-6-P + NADP+ —> 6-Phosphoglucono-δ-lactone + NADPH
enzyme?
Glucose-6-P Dehydrogenase
6-Phosphoglucono-δ-lactone + H2O —>
6-Phosphogluconate
6-Phosphoglucono-δ-lactone + H2O —> 6-Phosphogluconate
enzyme?
6-Phosphoglucono Lactonase
6-Phosphoglucono-δ-lactone + H2O —> 6-Phosphogluconate
rxn type?
hydrolysis
6-Phosphogluconate + NADP+ —> Ribulose-5-P + NADPH + CO2
enzyme?
6-Phosphogluconate Dehydrogenase
6-Phosphogluconate + NADP+ —> Ribulose-5-P + NADPH + CO2
reaction type?
oxidation, decarboxylatoon
6-Phosphogluconate + NADP+ —>
Ribulose-5-P + NADPH + CO2
3 Ribulose-5-P <—>
Ribose-5-P
2 Xylulose-5-P
Ribulose-5-P <—> Ribose-5-P
enzyme?
Ribulose-5-P Isomerase
Ribulose-5-P <—> Ribose-5-P
reaction type?
isomerization
Ribulose-5-P <—> Xylulose-5-P
type?
epimierization
Ribulose-5-P <—> Xylulose-5-P
enzyme?
Ribulose-5-P Epimerase
Ribose-5-P + Xylulose-5-P <—> Glyceraldehyde-3-P + Sedoheptulose-7-P
enzyme?
Transketolase
Ribose-5-P + Xylulose-5-P <—> Glyceraldehyde-3-P + Sedoheptulose-7-P
reactino type
Intermolecular Transfer of a C2 Unit (
Ribose-5-P + Xylulose-5-P <—>
Glyceraldehyde-3-P + Sedoheptulose-7-P
Glyceraldehyde-3-P + Sedoheptulose-7-P <—>
Fructose-6-P + Erythrose-4-P
Glyceraldehyde-3-P + Sedoheptulose-7-P <—> Fructose-6-P + Erythrose-4-P
enzyme?
Transaldolase
Glyceraldehyde-3-P + Sedoheptulose-7-P <—> Fructose-6-P + Erythrose-4-P
enzyme type?
Intermolecular Transfer of a C3 Unit
Erythrose-4-P + Xylulose-5-P <—> Fructose-6-P + Glyceraldehyde-3-P
enzyme?
Transketolase
Erythrose-4-P + Xylulose-5-P <—> Fructose-6-P + Glyceraldehyde-3-P
reaction type?
Intermolecular Transfer of a C2 Unit (Dihydroxyethyl)
Erythrose-4-P + Xylulose-5-P <—>
Fructose-6-P + Glyceraldehyde-3-P
As glycogen is depleted, gluconeogenesis kicks in using what as substrates?
lactate, pyruvate, CAC
intermediates, and most aa
what in glucogensis are the Three bypasses that circumvent three glycolytic steps that are irreversible?
what is the benefit to them?
The three Bypasses provide thermodynamically favored alternative steps
first step in glucogenesis?
what is used up?
pyruvate –> oxaloacetate
via pyruvate carboxylase
1 atp is used up in the activation of bicarbonate (which is needed to run the rxn)
pyruvate –> oxaloacetate
via ___
pyruvate carboxylase
pyruvate carboxylase catalyzes the carboxylation of the –___ group of Pyruvate
CH3
what is needed for pyruvate to be converted to oxaloacetate?
bicarbonate must be activated at the expense of an
ATP in a process that involves the enzyme’s prosthetic group, biotin
Bicarbonate is activated by the transfer of a__ from ATP
Phosphoryl group (PO3)
what convertes oxaloacetete to PEP?
y PEP carboxykinase,
what is generated from oxaloacetate —> PEP
what is consumed?
consumed? GDP goes to GTP
released? CO2
Gluconeogenesis begins in the ___
mitochondrion
• The only aa’s that cannot contribute to gluconeo are
Leu and Lys
One minor exception to mito as the starting point for gluconeogenesis is ____?
glycerol
glycerol which
gets converted to DHAP in the ___
cytosol
There is no transport system for OAA, but it can exit mito by the___ in reverse after first being reduced to malate.
Mal/Asp shuttle running
where is OAA converted back to?
cytosol
Human mito contain PEPCK, and there is a ___ transporter
PEP
All glycolytic reactions from ___ are reversible
PEP back to FBP
Bypass___, present in liver, is G6Pase
3
When ATP demands in muscle exceed the capacity of Ox Phos for generating ATP, ___ is produced
lactate
The lactate is carried to the liver where it is converted to
Glu and released back into the bloodstream
what is the cori cycle?
The lactate is carried to the liver where it is converted to Glu and released back into the bloodstream
the cori cycle after/durign exercise?
• After exercise this continues as muscle glycogen stores are replenished
what is oxygen debt
The amount of O2 consumed in liver during this rebuilding of muscle glycogen
