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Describe this diagram.
Harvesting electrons from citric acid cycle
The citric acid cycle oxidizes the ________ fragment of acetyl CoA to ____.
acetyl, CO2
In the process of oxidation, what are high energy electrons captured in the form of?
NADH, FADH2
First stage of citric acid cycle:
___ carbons are introduced into the cycle by _______________ of an acetyl group with a ____-carbon compound called ___________________.
The ___-carbon compound formed (__________) undergoes two ______________________________________, generating ____ molecules of CO2.
two
condensation
four
oxaloacetate
six
citrate
oxidative decarboxylations
two
CO2
Second stage of citric acid cycle:
____________________ is regenerated.
oxaloacetate
What do the first and second stage of the citric acid cycle have in common?
both generate high-energy electrons that are used to power the synthesis of ATP in oxidative phosphorylation
Describe this diagram.
Diagram of citric acid cycles
Describe this diagram.
Diagram of cellular respiration
What is step one of the citric acid cycle?
synthase catalyzes the condensation of acetyl CoA and oxaloacetate from citrate
irreversible reaction - very negative ΔG°’
synthase
enzyme that catalyzes a synthetic reaction in which two units are joined usually without the direct participation of ATP (or another nucleoside triphosphate)
What does oxaloacetate binding by citrate synthase induce?
Citrate synthase exhibits induced fit so it induces structural changes that lead to the formation of the acetyl CoA binding site
What does the formation of the reaction intermediate citryl CoA cause?
a structural change that completes active site formation.
citryl CoA is then cleaved to from citrate and coenzyme A
Describe this diagram.
Conformational changes in citrate synthase on binding oxaloacetate. The small domain of each subunit of the homodimer is shown in yellow; the large domains are shown in blue. (Left) Open form of enzyme alone. (Right) Closed form of the liganded enzyme.
What is step two of the citric acid cycle?
aconitrase catalyzes the isomerization of isocitrate from citrate
What is aconitase inhibited by?
a metabolite of fluoroacetate, which acts as a suicide inhibitor
Name three facts about fluoroacetate.
found in the genus Gastrolobium, a flowering plant native to Austrailia
animal poison that is produced naturally in some South African plants
converted into fluoroacety-CoA when ingested → reacts with citrate to form fluorocitrate (suicide inhibitor of Aconitase)
How does aconitase accomplish its role as a pesticide?
it shuts down the citric acid cycle and cellular respiration
What is step three of the citric acid cycle?
isocitrate dehydrogenase catalyzes the oxidative decarboxylation of isocitrate, forming α-ketoglutarate and capturing high-energy electrons as NADH
first oxidative decarboxylation
What is step four of the citric acid cycle?
α-Ketoglutarate dehydrogenase complex catalyzes the synthesis of succinyl CoA from α-ketoglutarate, generating NADH
second oxidative decarboxylation
What are the enzyme and the reactions of the α-ketoglutarate dehydrogenase complex structurally and mechanistically similar to?
pyruvate dehydrogenase complex
What does the multienzyme complex of the α-ketoglutarate dehydrogenase complex require?
thiamine pyrophosphate (TPP)
lipoic acid
FAD
Mg2+
A compound with high ____________-transfer potential is generated from succinyl coenzyme A.
phosphoryl
What is step five of the citric acid cycle?
succinyl CoA synthetase catalyzes the cleavage of thioester linkage and simultaneously powers formation of ATP
only substrate level phosphorylation in cycle
How is the formation of ATP by succinyl coenzyme A synthetase an example of a substrate-level phosphorylation?
succinyl phosphate (high-phosphoryl-transfer-potential compound) donates phosphate to ADP
Describe this diagram.
Reaction mechanism of succinyl CoA synthetase. The hydrolysis of the thioester bond provides the energy.
What three reactions of the citric acid cycle work together to catalyze successive reactions to regenerate oxaloacetate?
succinate dehydrogenase (step 6)
fumarase (step 7)
malate dehydrogenase (step 8)
third oxidation of cycle (from succinate)
What two organic byproducts are generated from steps 6-8 of the citric acid cycle?
FADH2
NADH
How is another citric acid cycle initiated from one citric acid cycle?
oxaloacetate can condense with another acetyl CoA
What is the only enzyme of the citric acid cycle not found in the mitochondrial matrix?
succinate dehydrogenase (embedded in inner mitochondrial membrane)
What is the fourth and final oxidation of the citric acid cycle?
malate dehydrogenase reaction
very positive ΔG°’
reaction pulled by citrate synthase reaction (next step)
What is the net reaction of the citric acid cycle?
How much ATP will be generated from the electrons from NADH?
2.5 ATP when used to reduce oxygen in the electron-transport chain
How much ATP will be generated from the electrons from FADH2?
1.5 ATP when used to reduce oxygen in the electron-transport chain
Describe this diagram.
Citric Acid Cycle. For each turn of the cycle, two carbons enter as an acetyl group and two carbons leave as molecules of CO2.
Describe this diagram.
This shows the reactions, enzymes, prosthetic groups, types and free energy differences for the eight steps of the citric acid cycle.
How are the two unfavored reactions in the citric acid cycle overcome?
Both of these reactions are followed by exergonic reactions, which means product of each reaction is removed thus allowing this reaction to proceed
How many carbon atoms are put into the citric acid cycle?
2 carbons (1 Acetyl CoA)
How many CO2 molecules are released from the citric acid cycle?
2 CO2 molecules
How many oxidations occur in the citric acid cycle?
4 ocidations
_ NADH, _ FADH2, _ GTP (_ ATP) are produced per turn of the citric acid cycle?
3 NADH
1 FADH2
1 GTP (1 ATP)
Pyruvate dehydrogenase complex balanced equation:
Citric acid cycle balanced equation:
Pyruvate dehydrogenase + citric acid cycle overall reaction equation:
Describe what these statements mean.
This shows that the oxidation of pyruvates forms CO2 and ATP.
What are the two key control points in the citric acid cycle?
the reactions catalyzed by isocitrate dehydrogenase and α-ketoglutarate dehydrogenase
What enzyme controls entry of glucose-derived acetyl CoA into the citric acid cycle?
pyruvate dehydrogenase
Describe this diagram.
The citric acid cycle is controlled at several points. The citric acid cycle is regulated primarily by the concentrations of ATP and NADH. The key control points are the enzymes isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.
What are the two most common inhibitors of steps of the citric acid cycle and the reaction catalyzed by pyruvate dehydrogenase?
ATP and NADH
What are many of the components of the citric acid cycle precursors for?
biosynthesis of key molecules
Describe this diagram.
Biosynthetic roles of the citric acid cycle. Intermediates are drawn off for biosyntheses (shown by red arrows) when the energy needs of the cell are met. Intermediates are replenished by the formation of oxaloacetate from pyruvate (green arrow).
Why are reactions that replenish citric acid cycle components required if the energy status of the cell changes?
These replenishing reactions are called __________ reactions.
because the citric acid cycle provides precursors for biosynthesis;
anaplerotic
A prominent anaplerotic reaction is catalyzed by ______________________, which synthesizes ________________ by the _______________ of pyruvate.
Recall that this reaction is also used in _______________________ and is dependent on the presence of _____________.
pyruvate carboxylase
oxaloacetate
carboxylation
gluconeogenesis
acetyl CoA
Describe this diagram.
How pyruvate carboxylase replenishes the citric acid cycle
How does the glyoxylate cycle differ from the citric acid cycle?
it bypasses the two decarboxylation steps, allowing synthesis of carbohydrates from fats
What can succinate be converted into before turning into glucose?
oxaloacetate
The _______________ cycle is prominent in oil-rich seeds such as sunflower seeds.
glyoxylate
Describe this diagram.
Overview of glyoxylate cycle
What are the two key enzymes of the glyoxylate cycle and their functions?
Isocitrate lyase: Catalyzes the cleavage of isocitrate to glyoxylate and succinate
Malate synthase: Catalyzes the reaction of glyoxylate with acetyl- CoA to produce malate
How many carbos are put into the glyoxylate cycle?
4 carbons (2-Acetyl CoA)
How many CO2 molecules are released from the glyoxylate cycle?
0
How many extra oxaloacetate molecules are produced from the glyoxylate cycle?
one
What is the net synthesis of the glyoxylate cycle?
glucose from Acetyl-CoA
What is the animals’ dilemma?
There is no net glucose synthesis from fat
NADH
NADH
GTP
FADH2
NADH
In the citric acid cycle, how many steps are involved in substrate level phosphorylation? What is the name of the enzyme?
1; succinyl CoA synthetase
In the citric acid cycle, how many steps are involved in decarboxylation? What is (are) the name of the enzyme?
2; isocitrate dehydrogenase, α-ketoglutarate dehydrogenase
In the citric acid cycle, how many steps are involved in oxidation-reduction? What is (are) the name of the enzyme?
4; isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinate dehydrogenase
Calculate the number of molecule of ATP that can be produced by substrate-level phosphorylation from two molecules of acetyl- CoA in the citric acid cycle and glyoxylate cycle.
the citric acid cycle - 2
glyoxylate cycle – 0
What conditions are required to obtain energy from acetyl CoA in the citric acid cycle? Select all that apply.
a) availability of O2
b) high energy charge
c) anaerobic conditions
d) low energy charge
a) availability of O2
d) low energy charge
What is the major purpose of the citric acid cycle?
a) reduction of NAD+ leading to the capture of high-transfer potential electrons
b) synthesis of citric acid
c) utilization of pyruvate
d) oxidation of carbon atoms leading to the capture of high-transfer potential electrons
d) oxidation of carbon atoms leading to the capture of high-transfer potential electrons
Two molecules of CO2 are produced each time a molecule of acetyl-CoA is oxidized. Do the carbon atoms of this acetyl-CoA molecule become the CO2 in the first turn of the cycle?
NO!!!
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