Chapter 16: TCA Cycle Flashcards
an unkempt, older man presents at the emergency department, he presents with edema around his ankles, shortness of breath, high blood pressure, tachycardia, and alcohol on his breath. After taking his social history, it becomes evident that he is experiencing homelessness, eats irregularly, if at all, and has become dependent on alcohol since “life got hard”, what vitamin deficiency explains the patient’s presentation?
a. lipoic acid
b. riboflavin
c. thiamine
d. vitamin C
c. thiamine
pyruvate decarboxylase requires thiamin pyrophosphate derived from vitamin B1, since chronic alcoholics have reduced B1 absorption in intestines then they would also be deficient in thiamine
which of the following TCA cycle reactions is not a redox reaction?
a. isocitrate DH
b. α-KGDH
c. succinate DH
d. fumarase
e. Malate DH
d. fumarase
the end product of glycolysis is _________, this molecule reacts with _____________ before entering the TCA cycle
a. pyruvate / HSCoA
b. lactate / NADH
c. Oxalo acetate / Acetyl CoA
d. AcetylCoA / glyoxylate
a. pyruvate / HSCoA
HSCoA = acetyl coenzyme A
what reaction does pyruvate dehydrogenase catalyze?
pyruvate + coenzyme A (CoA) –> acetyl-CoA
how many CO2 are generated in one cycle of the immediate TCA cycle?
a. 1
b. 2
c. 3
d. 4
e. 5
b. 2
which of the following is NOT directly required for the activity of pyruvate dehydrogenase?
a. ATP
b. HSCoA
c. lipoic acid
d. NAD+
e. FAD+
e. FAD+
the TCA cycle…
a. provides reducing equivalents under aerobic condition
b. provides intermediates for biosynthesis
c. uses most of the oxygen required under aerobic conditions
d. operating in different directions under aerobic and aerobic conditions
a. provides reducing equivalents under aerobic condition
b. provides intermediates for biosynthesis
the ∆G°’ of the reaction Malate + NAD+ -> OxAc + NADH+H+ is +29.7 KJ/mol, in the cell the reaction is favorable / not favorable because…
a. it does not really happen in the cell
b. it is followed by the citrate synthase reaction in the cell
c. it proceeds because OxAc concentrations are very low in the cell
d. is very unfavorable no matter what
not favorable but
c. it proceeds because OxAc concentrations are very low in the cell, making the Q very small and subsequently the reaction favorable
the following enzymes are linked to the reduction of NAD+ to NADH EXCEPT for ____
a. succinate dehydrogenase
b. isocitrate dehydrogenase
c. αKG dehydrogenase
d. pyruvate dehydrogenase
e. lactate dehydrogenase
a. succinate dehydrogenase
succinate dehydrogenase instead converts FAD to FADH2
the glyoxylate cycle is active in plants and in microbes to…
a. facilitate growth on 2- carbon compounds
b. allow the TCA cycle to run under anaerobic conditions
c. provide more reducing equivalents
d. generate additional ATP
a. facilitate growth on 2- carbon compounds
citrate synthase catalyzes the condensation reaction of AcetylCoA and OxAc. The ∆G⁰’ = -32.2 kJ/mol, what can you say about the concentration of citrate at equilibrium?
a. much higher than OxAc
b. much lower than OxAc
c. the same as OxAc
d. concentration depends on the conditions in the cell
a. much higher than OxAc
because more products than substrates implies a favorable reaction and therefore a negative delta G value
which is false for the glyoxylate cycle?
a. does not happen in humans
b. provides a way to grow on acetate as a carbon source
c. prevents the loss of carbon as CO2 in the TCA cycle
d. is located in the mitochondria
e. produces OxAc and succinate
d. is located in the mitochondria
the glyoxylate cycle actually takes place in the peroxisomes of plants
which of the following is/are true of the reactions and intermediates used in glycolysis and the TCA cycle?
a. pyruvate generated from fermentation is utilized in the TCA cycle
b. FADH is oxidized in the TCA cycle
c. TCA occurs in the mitochondrial matrix
d. both glycolysis and the TCA cycle occur in the cytosol in bacterial organisms
e. ATP hydrolysis drives the formation of NADH for later usage by the electron transport chain
b. FADH is oxidized in the TCA cycle
c. TCA occurs in the mitochondrial matrix
the pyruvate dehydrogenase complex (PDH) is a critical enzyme complex feeds those intermediates into the TCA cycle, which of the following are true of this metabolic step?
a. it produces NADH
b. it produces FADH2
c. it catalyzes the formation of acetylCoA by oxidation of an acetaldehyde
d. it releases CO2
e. it uses NADH and FADH2 as substrates
f. it involves the reduction of a reactive thiol group
a. it produces NADH
d. it releases CO2
f. it involves the reduction of a reactive thiol group
which is/are true of the pyruvate dehydrogenase complex (PDH)?
a. it is highly endergonic, allowing gluconeogenesis to occur after a meal
b. it is irreversible and results in the reduction of pyruvate
c. it requires ATP as part of the TCA cycle initiation
d. it minimizes the diffusion and loss of enzymatic substrates by its multi-subunit composition
b. it is irreversible and results in the reduction of pyruvate
d. it minimizes the diffusion and loss of enzymatic substrates by its multi-subunit composition
what are benefits of utilizing multi-enzyme complexes in metabolic pathways?
a. they easily scavenge ATP to drive reactions.
b. they minimize the usage of substrate by other enzymatic pathways
c. they are relatively energetically efficient
d. when combined, they yield a lower overall DG0’ for each individual enzyme within the complex
e. they can result in the reduction of multiple metabolic intermediates in quick succession
c. they are relatively energetically efficient
d. when combined, they yield a lower overall DG0’ for each individual enzyme within the complex
e. they can result in the reduction of multiple metabolic intermediates in quick succession
coenzyme A…
a. forms thioester acyl groups
b. has lipoic acid as one of its components
c. forms esters with relatively small standard free energies of hydrolysis
d. can have pyruvate linked to it through an ester linkage
a. forms thioester acyl groups
pyruvate is produced in glycolysis and used by the citric acid cycle which is located in the mitochondria, how does pyruvate get into the mitochondrial matrix?
a. it moves through the membrane by simple diffusion
b. diffusion is facilitated through a specific uniport
c. it transforms into acetate, which moves through a facilitated transporter
d. a transporter is not needed because pyruvate from glycolysis is already in the matrix
e. it moves through the malate shuttle system
b. diffusion is facilitated through a specific uniport
what is the advantage to having an enzyme complex, as in pyruvate dehydrogenase (PDH) complex?
a. multiple steps can be regulated at one point
b. products do not need to diffuse to become substrates for the next enzymatic reaction
c. products cannot be scavenged by other enzymes or pathways
d. conservation of energy drives the reactions
e. all of the answers are correct
e. all of the answers are correct
which statement regarding the citric acid cycle is FALSE?
a. part of the chemical logic behind it involves the conversion of the relatively unreactive methyl group of acetyl-CoA to a more reactive methylene group
b. the carbon atoms that feed into the cycle as acetyl-CoA do not leave as CO2 during their first turn in the cycle
c. it is found in the mitochondria of eukaryotes
d. its role is strictly limited to energy conservation during the catabolism of the acetyl group
d. its role is strictly limited to energy conservation during the catabolism of the acetyl group although the TCA cycle is central to energy-yielding metabolism, its role is not limited to energy conservation
which reaction in the TCA cycle is probably not strictly regulated?
a. ∆KG DH, ∆G⁰’ = -33 kJ/mol
b. malate DH, ∆G⁰’ = 29.7 kJ/mol
c. isocitrate DH, ∆G⁰’ = -32.2 kJ/mol
d. citrate synthase, ∆G⁰’ = -32.2 kJ/mol
b. malate DH, ∆G⁰’ = 29.7 kJ/mol
since malate DH is endergonic and unfavorable it does not need to be as strictly regulated
succinyl CoA synthetase catalyzes a(n)
a. redox reaction
b. substrate level phosphorylation
c. dehydration reaction
d. condensation reaction
e. oxidative phosphorylation
b. substrate level phosphorylation
acetaldehyde is produced by alcohol dehydrogenase after the consumption of alcohol, the molecule is very reactive and probably one of the main causes of hangover symptoms after overconsumption of alcohol,
acetaldehyde is also an intermediate during the oxidation of glucose generated by the enzyme pyruvate
dehydrogenase, why then does glucose overconsumption not lead to hangover symptoms?
during the metabolism of glucose the produced acetaldehyde is rapidly further metabolized to acetate, and its accumulation is minimized, additionally, the metabolism of glucose is tightly regulated, and the production of acetaldehyde is part of a controlled and balanced metabolic process, unlike the rapid and uncontrolled accumulation of acetaldehyde that occurs during alcohol metabolism
what is the yield so far for the degradation of one glucose through glycolysis and the TCA cycle?
____ ATP/GTP
____ NADH + H+
____ FADH2
2+2 ATP (GTP)
2+2+6 NADH + H+
2 FADH2
what is the oxygen requirement for the reaction of the TCA cycle?
there is no oxygen required for the TCA cycle
the last reaction in the TCA cycle (Malate + NAD+ –> OxAc + NADH + H+, ∆G°’ = +29. 7 KJ/mol) is very unfavorable under standard transformed conditions, explain how the cell achieves that this reaction readily can proceed in the cell
by coupling with other reactions and the quickly using the OxAc once it is produced the cell can proceed with the reaction, additionally the conversion of malate to oxaloacetate involves the reduction of NAD+ to NADH, the removal of NADH through subsequent steps or other cellular processes helps drive the reaction forward
the PyruvateDH complex is regulated by phosphorylation, indicate the metabolic effect (yes/no) in cells that do not make the phosphatase
a. Increased lactate ______
b. Increased pH ______
c. Increased citrate _______
d. Decreased NADH and ATP ______
a. Increased lactate ___yes___
b. Increased pH __no____
c. Increased citrate __yes_____
d. Decreased NADH and ATP __yes____
the MalateDH reaction is has a ∆G⁰’ = +23.7 kJ/mol
a. thus, under standard conditions the reaction is favorable / not favorable
b. how is this reaction affected by the citrate synthase reaction?
c. what must be true for the cellular concentrations of OxAc and Citrate in the cell?
a. not favorable
b. an unfavorable MalateDH reaction could potentially hinder the forward progression of the citrate synthase reaction due to the accumulation of oxaloacetate
c. they must be equal for the reaction to proceed
which of the following is FALSE regarding the glyoxylate cycle?
a. occurs in the mitochondrial matrix
b. allows organisms to subsist on 2-carbon energy sources
c. generates redox equivalents but no ATP
d. makes use of the same number of enzymes as the TCA cycle
d. makes use of the same number of enzymes as the TCA cycle
the ________________________ is important to move muscle lactate to the liver
cori cycle
carbon dioxide (CO2) is generated during in the____ __________
krebs cycle/TCA cycle
oxygen (O2) is used in the _____ ______
electron transport chain (ETC)
under anaerobic conditions NAD+ is regenerated by _____ _______
lactate fermentation
ATP is generated during __ ____
glycolysis
glucose is a substrate for _____ _____________ and is the product of ____ ________
gluconeogenesis, glycogen metabolism
acetyl CoA serves as an allosteric inhibitor of ____ ____
glyoxylate cycle
the ___ _____ allows plants and bacteria to grow on one- and two-carbon compounds
glyoxylate cycle
the _______ ____ generates sugars and reducing equivalents for nucleotide biosynthesis
pentose monophosphate pathway (PMP)
lactate is generated by ___ ____ and serves as a substrate for __ _____ in the liver
lactate fermentation, gluconeogenesis
