biochem lecture 9 pt 1 Flashcards
glwhat molecules can be used to synthesize glucose via gluconeogenesis
pyruvate, lactate, etc.
gluconeogenesis
synthesis of glucose from non carbon precursors
what are glycolysis and gluconeogenesis
opposite pathways
what do both pathways have in common
reciprocally regulated
what do mammals require to sustain us
carbs
where do we get carbs
diet, glycogen stores (liver and muscle), gluconeogenesis
absorptive phase
immediate access of glucose from the things we eatt
post-absorptive phase
short term starvation conditions; we rely on glycogen stores to provide glucose source
what do we rely on for glucose in short-term starvation conditions
glycogen stores
what happens if we don’t get more glucose (no more from diet or we’ve depleted stores)
we begin gluconeogenesis
how does gluconeogenesis initiate/progress
initiates slowly overtime, gradually increases to sustain organ function
what happens when you go beyond intermediate starvation to prolonged starvation (many days)
we see decrease in gluconeogenesis
why is there decrease in gluconeogenesis after a while
cuz there is a lack of carbon skeletons necessary to provide glucose via gluconeogenesis
what do you need in order to sustain life
supplementation of carbs
main sources of glucose needed to sustain life
dietary/exogenous, glycogen stores, and gluconeogenesis
when are glucose stores depleted
periods of starvation, fasting beyond a day
gluconeogenes invovles
pyruvate –> glucose
how many pyruvates do we need to make 1 glucose
2 pyruvates
what is required
2 NADH, 4 ATP, 2 GTP
glucogenic molecule
any molecule that can be converted into pyruvate
examples of glucogenic molecules
lactate, AAs, glycerol
so what does that mean if a molecule is glucogenic
can derive gluocse from that precursors
what are glycerol again
backbone of neutral fats
what are bypass reactions
unique to gluconeogenesis
describe bypass rxns
diff enzymes that catalyze a step in glycolysis, deff enzymes catalyzing the reverse step
what are irreversible glycolytic enzymes
hexokinase, PFK, pyruvate kinase
what are enzymes of gluconeogenesis
pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphate, glucose-6-phosphate
what are irreversible steps in glycolysis
exergonic
what are these steps then in other drxn
exergonic
each of these bypass rxns enzyme catalyzes what
an exergonic step
are these steps reversible or irreversible
technically reversible, but its mostly unidirectional so irreversible
what is importance of having unique enzymes
is something is unidirectional, then we can’t have the same enzymes
in order to have each of those steps occurring in one direction, and not influenced by flux, what do you need
need a different enzyme
how are the 3 glycolytic and 4 gluconeogenic enzymes controlled
reciprocally controlled by same hormones insulin and glucagon
describe example of this reciprocal control
if you’re stimulating glycolysis, means that 3 enzymes that catalyze 3 exergonic steps are gonna be active, while simultaneous inactivation of gluconeogenic bypass rxn enzymes
what is understanding the importance of bypass rxns crucial force
understanding how we have reciprocal control in a seemingly reversible process (glycolysis vs. gluconeogenesis)
what are key points of regulation going to involve
these bypass reactions
what 4 enzymes are bypass reactions in gluconeogenesis catalyzed by
pyruvate carboxylase, phosphoenolpyruvate carboxylase, fructose-1,6-bisphosphatase, glucose-6-phosphotase
why is it 4 steps instead of 3
process for PEP to pyruvate conversion in glycolysis is one step BUT pyruvate to PEP is two step process (via formation of oxaloacetate)
what catalyzes the first step in pyruvate to PEP
pyruvate carboxylase
what catalyzes the 2nd step
phosphoenolpyruvate carboxylase
what enzyme catalyzes the bypass of pyruvate kinase
pyruvate carboxylase
what do carboyxlaes do
tack on carbons to structures
what do decarboxylases do
remove carbons from structure
what does pyruvate carboxylase do
addition of carbon in form of bicarbonate to pyruvate, generates oxaloacetate
what rxn does pyruvate carboxylase do
pyruvate –> oxaloacetate
what rxn (thermodynamically speaking) is pyruvate carboxylase catalyzing
exergonic or irreversible step
what cofactor requirement do carboxylases have
biotin
what activates carboxylase
acetyl CoA
what is acetyl CoA an indicator of
low E state in the cell;
what is acetyl CoA serving as low E indicator important for
important for catalyzing synthesis of glucose
what kinda rxn is this first bypass step
anaplerotic rxn
what is an anaplerotic rxn
rxns that replenish intermediates in a pathway
what is oxaloacetate synthesized for
final product in TCA: in order to keep eTCA going, we have synthesis of oxaloacetate thru this bypass rxn
what does the second enzyme do
oxaloacetate –> phosphoenolpyruvate
what enzyme for second one
phosphoenolpyruvate carboxykinase (PEPCK)
when does PEPCK synthesis increase
increases in fasting
where does first bypass step occur
pyruvate to oxaloacetate conversion is in mitochondrial matrix
where does second bypass step occurs
in cytosol
so what is needed in order for gluconeogenesis to occur
oxaloacetate needs to go thru interconversion steps involving malate formation
describe thermodynamics of pyruvate carboxylase
metabolically irreversible
what does pyruvate use as a cofacto
biotin
what is pyruvate carboxylase allosterically activated by
acetyl CoA
what kinda rxn is pyruvate carboxylase step
anaplerotic for TCA cycle
how is pyruvate carboxylase anaplerotic for TCA cycle
cuz it replenishes oxaloacetate for TCA cycle
where does pyruvate carboxylase step occur
mitochondria
what is biotin utilized by
carboxylase
how is biotin utilized
covalently associated to specific lysine residue in active site of carboxylase
what happens to pyruvate and where
pyruvate is carboxylated into oxaloacetate, by pyruvate carboxylase, in mitochondria
what is needed for pyruvate to enter gluconeogenic pathway
needs to enter mitochondrial matrix
how does pyruvate get into mitochondrial matrix
specific transporters
basically what is needed for pyruvate to go into TCA cycle
needs to get into mitochondrial matrix
what happens to pyruvate in mitochondria
converted to oxaloaecetate by pyruvate carboxylase
what happens to oxaloacetate in mitochondria
converted to malate
who does oxaloacetate –> malate
malate dehydrogenase
what does oxaloacetate to malate conversion allow for
export of carbon skeletons originally derived from pyruvate back into cytosol from mitochondrial matrix
sum up conversion step in first two bypass rxns
pyruate –> oxaloacetate (in mitochondria) –> malate (shuttled out of mitochondria) –> oxaloacetate
why do we need to do a bunch of conversion reactions
becuase there is no oxaloacetate transporter, so it can’t be shuttled out of mitochondria
what enzyme carries out this interconversion
malate dehydrogenase
sum up what malate dehydrogenase does
oxaloacetate –> malate (by malate dehydrogenase), malate shuttled out of mitochondria into cytosol, then cytosolic malate dehydrogenase which does malate –> oxaloacetate
what enzyme does oxaloacetate –> malate
malate dehydrogenase
what enzyme does malate –> oxaloacetate
cytosolic malate dehydrogenase
what happens once we get malate –> oxaloacetate
we can continue on w/ gluconeogenesis
what is 3rd bypass rxn
fructose -1,6-bisphosphate –> fructose-6-phosphate
what enzyme for 3rd bypass rxn
fructose-1,6-bisphosphatase
what kinda rxn (thermodynamically) is fructose-1,6-bisphosphatase
metabolically irreversible rxn
what are allosteric inhibitors of F-1,6-BPase
AMP, fructose-2,6-bisphosphate
what is the glycolytic counterpart for this 3rd bypass rxn
conversion of F6P into F,1-6-BP
what enzyme in glycolysis
PFK-1
why do we require diff enzymes
both exergonic steps but occurring in opposite directions, so diff enzymes needed
describe reciprocal control in gluconeogenesis and glycolysis
if one enzyme active other one is gonna be shut down
what is fructose-2,6-bisphosphate important for
reciprocal regulation of these two enzymes
what is final bypass step of gluconeogenesis
glucose-6-phosphate –> glucose
what enzyme catalyzes final bypass step
glucose-6-phosphatase
describe thermodynamics of this final bypass rxn
irreversible
what kinda rxn is G6P to glucose
hydrolysis rxn
where is glucose-6-phosphatase found
only liver and kidney
so only which tissues can serve as as source of glucose from gluconeogenesis
liver and kidney
what enzyme catalyzes the glycolytic counterpart
hexokinase
what are we doing to glucose-6-phosphate to glucose
dephosphorylating it
why do we phosphorylate glucose to G6P
traps it inside cell
what would happen without glucose-6-phosphatase in gluconeogenesis
that glucose would be trapped in cell, can’t go to other parts of body; so we need to dephosphorylate it
what is main source of glucose via gluconeogenesis
liver, little bit from kidney
what is glucose-6-phosphate a precursor for
glycogen and glucose synthesis
where is glucose-6-phosphatase found in
only liver and kidney
where is glucose-6-phosphatase hgihly regulated
in liver
what is glucose-6-phosphate a starting point for
pentose phosphate pathway
is glucsoe-6-phosphatase expressed in every tissue or only limited ones
limited tissue expression; only liver and kidney
where are major contributions/release of glucose into blood gonna come from
liver mainly
so why is liver strictly regulating glucose-6-phosphatase enzyme
because major contributions/release of glucose come from the liver
how many NTPS (so like ATP/GTP) does it take to synthesize glucose
6 NTPs
how many NTPs are generated from glycolysis
2 nucleotide triphosphate molecules
is gluconeogenesis favorable or unfavorable
unfavorable (because we are synthesizing something)
how much extra high phosphoryl transfer potential molecules does it take to drive this unfavorable gluconeogenesis pathway
4 extra
how many pyruvates required to make glucose
2 pyruvates
what does gluconeogenesis require
some investment of ATP E
why do we need an input of E to synthesize glucose
because it’s endergonic
does that E needed to synthesize glucose only come from ATP
no; body needs additional E sources
where is flux through a pathway controlled at
rate-limiting steps
how can flux thru the rate determining steps be altered
allosteric control, covalent modifications, substrate cycles/futile cycles, genetic control (regulate transcription/translation of enzymes)
what can you do when you have 2 directly opposing pathways
reciprocal control
why can we control flow of intermediates thru these pathways at these exergonic rate limiting steps
because these steps are unidirectional; by limiting or depleting reactant of that step, you can limit the amount of byproduct produced in that step
what are reciprocally regulated in the liver
glycolysis and gluconeogenesis
what does this reciprocal regulation allow
prevents both pathways from operating at the same time
what does high. [AMP] indicate for glycolysis and gluconeogenesis
low energy state; need ATP
what does high [ATP] mean
high E state, intermediates are abundant
what is another allosteric regulator of gluconeogenesis/glycolysis
citrate concentration
high [citrate] means
high energy state, abundant intermediates
what does insulin stimulate
glycolysis
what does glucagon stimulate
gluconeogenesis
what are allosteric regulators
AMP, ATP, citrate
what is liver a major site for
major site for carb metaboism
what does insulin promote
glucose uptake and storage in liver, thus glycolysis
what does insulin do in other tissues
inhibits glycolysis
what does insulin do in liver
stimulates glycolysis; important for generating ATP E, necessary to fuel glycogenolysis, etc.
what does glucagon stimulate
gluconeogenesis
when is glucagon activated
intermediate starvatino conditions
what do the points of control for allosteric regulation primarily involve
bypass reactions
what are indicators of a high E state in the celly
acetyl CoA, ATP, citrate
what do high E state indicators stimulate
gluconeogenesis
what are low E state indicators
AMP, ADP
what do low E state indicators do
inhibit gluconeogenesis
what does high AMP indicate
energy state is low, so we need ATP
what does low E state do
stimulates glycolysis while reciprocally inhibiting gluconeogenesis
what does a lot of ATP, TCA cycle intermediates (citrate, acetyl CoA) mean
high E state
what are allosteric regulators here
ATP/ADP/AMP, TCA cycle intermediates (citrate/acetyl CoA)
what does ATP and TCA cycle intermediates do
inhibits glycolysis and stimulate gluconeogenesis
describe futile cycle
what happens if both gluconeogenesis and glycolysis were activated; gluconeogenesis: fructose-1,6-bisphosphate –>fructose-6-phosphate, and then fructose-6-phosphate –> fructose-1,6-bisphosphate in glycolysis. if both enzymes active at the same time, it would be a futile cycle
is futile cycle actually happening
nope; whenever one enzyme is active, the reciprocal enzyme is inactive
what is a big part to understanding what futile cycles are
understanding that they do reciprocal regulation of enzymes catalyzing the opposing step in that cycle
consider FBP-ase 1 (gluconeogenic enzyme) and PFK-1 (glycolytic enzyme). what is an important regulator for both enzymes
fructose-2,6-bisphosphate
what is fructose-2,6-bisphosphate
isomer of fructose-1,6-bisphosphate
is F-2,6-BP a player in gluconeogenesis/glycolysis?
no; it is not serving as an intermediate in either of these 2 pathways
what is fructose-2,6-bisphosphate form important for
reciprocal regulation of PFK-1 and FBPase-1
what does fructose-2,6-bisphosphate serve as
allosteric regulator of these two enzymes
what does fructose-2,6-bisphosphate do to PFK-1 and FBPase-1
activates PFK-1 (glycolysis) while simultaneously inhibiting FBPase-1 (gluconeogenic enzyme)
what do high levels of F26BP favor
activation of PFK-1
what does activation of PFK-1 favor
glycolysis
what kind of regulation is that of PFK-1 and FBPase 1 by F-2,6-BP
reciprocal regulation
what does F26BP’s regulation of PFK-1 and FBPase-1 involve
two more enzymes
what are these 2 more enzymes called
PFK-2 and FBPase-2
are PFK-2 and FBPase-2 the same as PFK-1 and FBPase-1
nope
what does PFK-2 correspond to
formation of F-26-BP
what does FBPase-2 correspond to
reduction in F-2,6-BP levels
so what are these enzymes with 2 in their names involved in
regulation or control of level of F,2-6-BP
what does active PFK-2 favor
formation of fructose-2,6-bisphosphate
what does increase in fructose-2,6-bisphosphate do
activates PFK-1 while inhibiting FBPase-1
what does activates PFK-1 while inhibiting FBPase-1 do
favors glycolysis
basically what does PFK-2 being active do
increase in F-2,6-BP, increases PFK-1, inhibits FBPase-1, which favors glycolysis
what does FBPase-2 do
dephosphorylates fructose-2,6-bisphosphate do
what does de-phosphorylating fructose-2,6-bisphosphate do
lowers levels of F-2,6-BP
what does lowering F26BP do
less activation of PFK-1 (so less PFK1) and less inhibition of FBPase-1 (so more FBPase-1)
what does less PFK1 and more FBPase-1 do
favors gluconeogenesis and inhibits glycolysis
basically what does active FBPase-2 do
decrease in F-2,6-BP, so decrease PFK-1, increasees FBPase-1, which favors gluconeogenesis
can hormones stimulate futile cycle
yes
what does glucagon do
stimulates gluconeogenesis
what does glucagon in liver do
inhibits glycolysis
how does glucagon work in futile cycle
simulates cAMP, activates PKA, phosphorylates FBPase-2 and PFK2
what does PKA do to FBPase-2 and PFK-2
phosphorylates them
what does phosphorylating FBP-ase 2 do
activates it
what does phosphorylating PFK-2 do
inhibits it
so describe what glucagon does in futile cycle
glucagon –> cAMP –> PKA –> activates FBPase2, inhibits PKA-2 –> lowers F-2,6-BP –> inhibits PFK-1 and activates FBPase-2 –> favors gluconeogenesis and inhibits glycolysis
if glucagon is active, does that mean higher or lower levels of fructose-2,6-bisphosphate
lower levels of f-2,6-bp
what does glucagon do
stimulates gluconeogenesis
how does glucagon stimulate gluconeogenesis in liver
lby lowering F-26-BP, activates FBPase-1 and inhibits PFK-1, activating gluconeogenesis
what does insulin do
favors glycolysis, inhibits gluconeogenesis
what other enzyme is at play in futile cycle
PP2
how does insulin work in futile cycle
insulin activates PP2
what does PP2 do to PFK2 and FBPase-2
dephosphorylates them
what does dephosphorylating of PFK-2 by PP2 do
activates PFK-2
what does dephosphorylating FBPase-2 by PP2 do
inactivates FBPase-2
what does PP2’s dephosphorylating activity do to F-26-BP
activates it
so what does insulin do to f-26-bp
increases fructose-2,6-bp
what does increasing f-26-bp do
activates PFK-1, inhibits FBPase-1, favors glycolysis over gluconeogenesis
what does insulin do in futile cycle (full pathway)
insulin –> PP2 –> inactivates FBPase2, activates PKA-2 –> increases F-2,6-BP –> increases PFK-1 and decreases FBPase-2 –> favors glycolysis and inhibits gluconeogenesis
what does cori cycle involve
interconversion of waste products, their recycling to synthesize more glucose in liver via gluconeogenesis
what was one of the issues with gluconeogenesis
we don’t have enough NTP equivalence from glycolysis to fuel gluconeogenesis
what would we end up with if we just relied on glycolysis to fuel gluconeogenesis
energy deficiency
corci cycle
describes interconnectedness b/w glycolysis and gluconeogenesis, specificaly where ATP needed to drive gluconeogenesis comes from
where does ATP oxidation needed to drive gluconeogenesis come fom
beta oxidation of fats in liver
overall what happens in cori cycle
pyruvate (lactic acid) generated thru fermentation accumulates in muscle, travels to liver, converted back to pyruvate, and goes thru gluconeogenesis to synthesize glucose
what can happen in intermediate starvation conditions
that glucose can be used in glycolysis, like in muscle, brain, etc.
what is gluconeogenic pathway coupled to
some ATP generated via oxidation of fatty acids
what is cori cycle important for understanding
important in understanding linkage and thus how gluconeogenesis and glycolysis are regulated
what happens as a result of liver being a major organ for intermediary metabolism
a lot of blood flow into and out of liver
how are energy rich molecules and nutrients available from diet made available
partial digestion in stomach and upper parts of intestines
where do those energy rich molecules go
transported to liver
how are E rich molecules transported to liver
via blood flow via hepatic portal system
how are those products from liver distributed to various parts of body
byproducts of the various metabolic processes that occur from liver leads to its distribution
what does massive amount of bloodflow into and out of liver allow
means you can distribute intermediates of carb metabolism AND fatty acid metabolism, protein metabloism
what is liver a big time player in
distribution of various types of dietary fuels, receiving waste products and intermediates that can be used in recycling pathways (like in cori cycle)
what is cori cycle interaction b/w
interaction of glycolysis and gluconeogenesis
describe cori cycle step 1
lactate from peripheral tissues goes to liver and made to glucose (lactate –> glucose in liver)
cori cycle step 2
glucose goes back to peripheral tissues (like muscle)
cori cycle step 3
uses lipid for energy
talk about placement of liver in circulation
first pass at removing nutrients absorbed from intestine, makes nutrients available to other tissues
what does liver participate in
interconversion of all types of metabolic fuels (carbs, AAs, fatty acids)
what does liver regulate
distribution of dietary fuels, supplies fuel from its own reserves
where does liver supply fuel
from its own reserves
what does cori cycle do
generates ATP
how does cori cycle make ATP
(lactate –> glucose –> lactate) thru this interconversion
