BICH 409 EXAM 4 /FINAL EXAM QUESTIONS WITH
VERIFIED ANSWERS
What is gluconeogenesis? - answers - the synthesis of glucose from noncarbohydrate
precursors
What is the primary energy source for the brain? - answers - glucose
When must glucose be synthesized from noncarbohydrate precursors in order to
maintain the blood glucose levels? - answers - for fasting periods longer than one day,
or during periods of intense exercise
What are the noncarbohydrate precursors used in gluconeogenesis? - answers - -
pyruvate
- lactate
- oxaloacetate
- gluconeogenic amino acids
- glycerol
In what forms do the noncarbohydrate precursors enter the gluconeogenic pathway? -
answers - - pyruvate
- oxaloactate
- dihydroxyactetone phosphate
What are the two major sites for gluconeogenesis? - answers - the liver (90%) and the
kidneys (10%)
What are the three irreversible steps of glycolysis catalyzed by, which are the steps that
have to be bypassed in gluconeogenesis? - answers - - hexokinase
- phosphofructokinase
- pyruvate kinase
How many ntps does gluconeogenesis consume in order to make it a spontaneous
(exergonic) process? - answers - six
What are the two steps required to convert pyruvate back into phosphoenolpyruvate
(pep) during gluconeogenesis? - answers - 1. Pyruvate carboxylase (co2 + atp + h2o -->
adp + pi + 2h+): carboxylation of pyruvate to form oxaloacetate
2. Pep carboxykinase (gtp --> gdp + co2): oxaloacetate is decarboxylated and
phosphorylated to produce phosphoenolpyruvate
What enzyme aids the process to overcome the generation of fructose-6-phosphate
from fructose-1,6-bisphosphate? - answers - fructose-1,6-bisphosphatase
,What is the enzyme that overcomes the irreversible step catalyzed by hexokinase which
is the phosphorylation reaction converting glucose-6-phosphate into glucose? - answers
- glucose-6-phosphatase
Where is glucose-6-phosphatase found? - answers - - the lumen of the endoplasmic
reticulum
- not present in the muscles or the brain so glucose cannot be produced by these
organs
Where does pyruvate carboxylase get its energy and what does it do? - answers - it
uses the energy of atp to carboxylate pyruvate to form oxaloacetate
What does the enzyme pyruvate carboxylase require? - answers - biotin, a cofactor that
is covalently attached to a lysine residue
What does biotin carry? - answers - it serves as a carrier of activated carbon dioxide
What is the first step of pyruvate carboxylase? - answers - to activate a molecule of
bicarbonate for nucleophilic attack
How is bicarbonate activated? - answers - - by phosphorylation with atp to produce a
high energy carboxyphosphate intermediate
What is the second step in the reaction of pyruvate carboxylase? - answers -
carboxyphosphate then undergoes nucleophilic attack by the n1 atom of biotin to form
n-carboxybiotin
What is the third step in the reaction of pyruvate carboxylase? - answers - to remove a
proton from the c3 of pyruvate to generate a resonance stabilized carbanion which is a
good nucleophile, attacking the n-carboxybiotin to regenerate biotin and form
oxaloacetate
What allosterically activates pyruvate carboxylase? - answers - acetyl-coa
What is necessary of acetyl-coa in order to activate bicarbonate? - answers - acetyl-coa
must be bound to an allosteric binding site of the enzyme
What is the second half of the pyruvate carboxylase catalyzed reaction? Is his affected
by the allosteric regulator acetyl-co-a? - answers - - the nucleophilic attack of the
pyruvate enolate on n-carboxybiotin
- no
What is the physiological regulation of the activation of bicarbonate by acetyl-coa? -
answers - - if the concentration of atp is low (atp is a substrate for pyruvate carboxylase)
and/or the concentration of acetyl-coa is low, then pyruvate is directed into the citric acid
cycle to promote the synthesis of atp
,- if the concentration of atp and acetyl-coa are high, pyruvate is converted into
oxaloacetate and consumed in gluconeogenesis
- high concentrrations of atp and acetyl-coa are signals that the cell's energy level is
high and metabolites are converted into glucose
- if the energy status of the cell is low, the concentrations of atp and acyl-coas are low
and pyruvate is directed towards the tca cycle (citric acid).
Where is the only place pyruvate carboxylase is found? - answers - in the matrix of the
mitochondria
Following pyruvate carboxylase, what is the next enzyme involved in gluconeogenesis?
- answers - pep carboxykinase (phosphoenolpyruvate carboxykinase)
What are the two places pep carboxykinase is found? - answers - in both the
mitochondria or in the cytosol
(depends on the organism and the tissue)
Where is pep carboxykinase found in human livers? - answers - in both the
mitochondria and the cytosol
Where is pyruvate transported and what is it converted into once it gets there? -
answers - - transported into the mitochondria
- converted into acetyl-coa by pyruvate dehydrogenase --> citric acid cycle or
- converted into oxaloacetate by pyruvate carboxylase and used for gluconeogenesis
Which enzyme converts pyruvate into acetyl-coa for use in the citric acid cycle? -
answers - pyruvate dehydrogenase
Which enzyme converts pyruvate into oxaloacetate for use in gluconeogenesis? -
answers - pyruvate carboxylase
What happens in tissues where pep carboxykinase is found only in the mitochondria?
Where can this enzyme be transported? - answers - - oxaloacetate is converted into
pep
- can be transported to the cytosol
What happens in tissues where pep carboxykinase is found only in the cytosol? -
answers - oxaloacetate must be reduced to malate so that it can be transported across
the mitochondrial membrane to the cytosol where the malate is reoxidized into
oxaloacetate and goes on through gluconeogenesis
What two things does the enzyme pep carboxykinase do simultaneously? - answers -
decarboxylates and phosphorylates oxaloacetate
What happens to the co2 in the mechanism of pep carboxykinase? - answers - - co2 is
added in the pyruvate carboxylase step
, - this co2 comes off in the pep carboxykinase step
Is the decarboxylation in the mechanism of pep carboxykinase endergonic or
exergonic? What does this process help to drive? - answers - - it is very exergonic
- helps to drive the otherwise highly endergonic reaction of pep synthesis
What happens after pep is formed by pep carboxykinase? - answers - - the pep is
hydrated by enolase to form 2-phosphoglycerate which is in turn isomerized into 3-
phosphoglycerate by phosphoglycerate mutase
- phosphoglycerokinase uses atp to produce 1,3-bisphosphoglycerte which is reduced
by gapdh into glyceraldehyde-3-phosphate
Which enzyme produces dihydroxyacetone phosphate? - answers - triose phosphate
isomerase
Which enzyme catalyzes an aldol condensation of dhap and glyceraldehyde-3-
phosphate to form fructose-1,6-bisphosphate? - answers - aldolase
Which enzymes function in both glycolysis and gluconeogenesis, and why? - answers -
- pep carboxykinase
- enolase
- phosphoglycerate mutase
- phosphoglycerokinase
- triose phosphate isomerase
- aldolase
- because they are all near equilibrium and reversible
What is the first committed step of glycolysis and what enzyme catalyzes it? Is it
reversible or irreversible? - answers - - phosphofructokinase
- the phosphorylation of fructose-6-phosphate by phosphofructokinase
- irreversible
In gluconeogenesis, which enzyme hydrolyzes fructose-1,6-bisphosphate? What type of
regulation is this enzyme? - answers - - fructose-1,6-bisphosphatase
- allosterically regulated enzyme
The reaction of the phosphorylation and/or hydrolyzation of fructose-1,6-bisphosphate is
(exergonic/endergonic), (reversible/irreversible), and (non-regulated/regulated). -
answers - - exergonic
- irreversible
- regulated
Does the reaction involving fructose-1,6-bisphosphate increase, decrease, or have no
effect on the following:
- citrate
- fructose-2,6-bisphosphate
VERIFIED ANSWERS
What is gluconeogenesis? - answers - the synthesis of glucose from noncarbohydrate
precursors
What is the primary energy source for the brain? - answers - glucose
When must glucose be synthesized from noncarbohydrate precursors in order to
maintain the blood glucose levels? - answers - for fasting periods longer than one day,
or during periods of intense exercise
What are the noncarbohydrate precursors used in gluconeogenesis? - answers - -
pyruvate
- lactate
- oxaloacetate
- gluconeogenic amino acids
- glycerol
In what forms do the noncarbohydrate precursors enter the gluconeogenic pathway? -
answers - - pyruvate
- oxaloactate
- dihydroxyactetone phosphate
What are the two major sites for gluconeogenesis? - answers - the liver (90%) and the
kidneys (10%)
What are the three irreversible steps of glycolysis catalyzed by, which are the steps that
have to be bypassed in gluconeogenesis? - answers - - hexokinase
- phosphofructokinase
- pyruvate kinase
How many ntps does gluconeogenesis consume in order to make it a spontaneous
(exergonic) process? - answers - six
What are the two steps required to convert pyruvate back into phosphoenolpyruvate
(pep) during gluconeogenesis? - answers - 1. Pyruvate carboxylase (co2 + atp + h2o -->
adp + pi + 2h+): carboxylation of pyruvate to form oxaloacetate
2. Pep carboxykinase (gtp --> gdp + co2): oxaloacetate is decarboxylated and
phosphorylated to produce phosphoenolpyruvate
What enzyme aids the process to overcome the generation of fructose-6-phosphate
from fructose-1,6-bisphosphate? - answers - fructose-1,6-bisphosphatase
,What is the enzyme that overcomes the irreversible step catalyzed by hexokinase which
is the phosphorylation reaction converting glucose-6-phosphate into glucose? - answers
- glucose-6-phosphatase
Where is glucose-6-phosphatase found? - answers - - the lumen of the endoplasmic
reticulum
- not present in the muscles or the brain so glucose cannot be produced by these
organs
Where does pyruvate carboxylase get its energy and what does it do? - answers - it
uses the energy of atp to carboxylate pyruvate to form oxaloacetate
What does the enzyme pyruvate carboxylase require? - answers - biotin, a cofactor that
is covalently attached to a lysine residue
What does biotin carry? - answers - it serves as a carrier of activated carbon dioxide
What is the first step of pyruvate carboxylase? - answers - to activate a molecule of
bicarbonate for nucleophilic attack
How is bicarbonate activated? - answers - - by phosphorylation with atp to produce a
high energy carboxyphosphate intermediate
What is the second step in the reaction of pyruvate carboxylase? - answers -
carboxyphosphate then undergoes nucleophilic attack by the n1 atom of biotin to form
n-carboxybiotin
What is the third step in the reaction of pyruvate carboxylase? - answers - to remove a
proton from the c3 of pyruvate to generate a resonance stabilized carbanion which is a
good nucleophile, attacking the n-carboxybiotin to regenerate biotin and form
oxaloacetate
What allosterically activates pyruvate carboxylase? - answers - acetyl-coa
What is necessary of acetyl-coa in order to activate bicarbonate? - answers - acetyl-coa
must be bound to an allosteric binding site of the enzyme
What is the second half of the pyruvate carboxylase catalyzed reaction? Is his affected
by the allosteric regulator acetyl-co-a? - answers - - the nucleophilic attack of the
pyruvate enolate on n-carboxybiotin
- no
What is the physiological regulation of the activation of bicarbonate by acetyl-coa? -
answers - - if the concentration of atp is low (atp is a substrate for pyruvate carboxylase)
and/or the concentration of acetyl-coa is low, then pyruvate is directed into the citric acid
cycle to promote the synthesis of atp
,- if the concentration of atp and acetyl-coa are high, pyruvate is converted into
oxaloacetate and consumed in gluconeogenesis
- high concentrrations of atp and acetyl-coa are signals that the cell's energy level is
high and metabolites are converted into glucose
- if the energy status of the cell is low, the concentrations of atp and acyl-coas are low
and pyruvate is directed towards the tca cycle (citric acid).
Where is the only place pyruvate carboxylase is found? - answers - in the matrix of the
mitochondria
Following pyruvate carboxylase, what is the next enzyme involved in gluconeogenesis?
- answers - pep carboxykinase (phosphoenolpyruvate carboxykinase)
What are the two places pep carboxykinase is found? - answers - in both the
mitochondria or in the cytosol
(depends on the organism and the tissue)
Where is pep carboxykinase found in human livers? - answers - in both the
mitochondria and the cytosol
Where is pyruvate transported and what is it converted into once it gets there? -
answers - - transported into the mitochondria
- converted into acetyl-coa by pyruvate dehydrogenase --> citric acid cycle or
- converted into oxaloacetate by pyruvate carboxylase and used for gluconeogenesis
Which enzyme converts pyruvate into acetyl-coa for use in the citric acid cycle? -
answers - pyruvate dehydrogenase
Which enzyme converts pyruvate into oxaloacetate for use in gluconeogenesis? -
answers - pyruvate carboxylase
What happens in tissues where pep carboxykinase is found only in the mitochondria?
Where can this enzyme be transported? - answers - - oxaloacetate is converted into
pep
- can be transported to the cytosol
What happens in tissues where pep carboxykinase is found only in the cytosol? -
answers - oxaloacetate must be reduced to malate so that it can be transported across
the mitochondrial membrane to the cytosol where the malate is reoxidized into
oxaloacetate and goes on through gluconeogenesis
What two things does the enzyme pep carboxykinase do simultaneously? - answers -
decarboxylates and phosphorylates oxaloacetate
What happens to the co2 in the mechanism of pep carboxykinase? - answers - - co2 is
added in the pyruvate carboxylase step
, - this co2 comes off in the pep carboxykinase step
Is the decarboxylation in the mechanism of pep carboxykinase endergonic or
exergonic? What does this process help to drive? - answers - - it is very exergonic
- helps to drive the otherwise highly endergonic reaction of pep synthesis
What happens after pep is formed by pep carboxykinase? - answers - - the pep is
hydrated by enolase to form 2-phosphoglycerate which is in turn isomerized into 3-
phosphoglycerate by phosphoglycerate mutase
- phosphoglycerokinase uses atp to produce 1,3-bisphosphoglycerte which is reduced
by gapdh into glyceraldehyde-3-phosphate
Which enzyme produces dihydroxyacetone phosphate? - answers - triose phosphate
isomerase
Which enzyme catalyzes an aldol condensation of dhap and glyceraldehyde-3-
phosphate to form fructose-1,6-bisphosphate? - answers - aldolase
Which enzymes function in both glycolysis and gluconeogenesis, and why? - answers -
- pep carboxykinase
- enolase
- phosphoglycerate mutase
- phosphoglycerokinase
- triose phosphate isomerase
- aldolase
- because they are all near equilibrium and reversible
What is the first committed step of glycolysis and what enzyme catalyzes it? Is it
reversible or irreversible? - answers - - phosphofructokinase
- the phosphorylation of fructose-6-phosphate by phosphofructokinase
- irreversible
In gluconeogenesis, which enzyme hydrolyzes fructose-1,6-bisphosphate? What type of
regulation is this enzyme? - answers - - fructose-1,6-bisphosphatase
- allosterically regulated enzyme
The reaction of the phosphorylation and/or hydrolyzation of fructose-1,6-bisphosphate is
(exergonic/endergonic), (reversible/irreversible), and (non-regulated/regulated). -
answers - - exergonic
- irreversible
- regulated
Does the reaction involving fructose-1,6-bisphosphate increase, decrease, or have no
effect on the following:
- citrate
- fructose-2,6-bisphosphate
