In what part of the cell does the citric acid cycle take place? Does this differ from the part of the cell where glycolysis occurs?
The citric acid cycle takes place in the mitochondral matrix. Glycolysis takes place in the cytosol
What electron acceptors play a role in the citric acid cycle?
NAD+ and FAD are the primary electron acceptors of the citric acid cycle
How many enzymes are involved in mammalian pyruvate dehydrogenase? What are their function?
Five enzymes are involved. Pryuvate dehydrogenase transfers a two carbon unit to TPP and releases CO2. Dihydrolipoyl transacetylase transfers the two carbon acetyl unit to lipoic acid and then to coenzyme A. Dihydrolipoyl dehydrogenase reoxidizes lipoic a
In the PDH reaction alone, we can see cofactors that come from four different vitamins. What are they?
Thiamine pyrophosphate comes from B vitamin Thiamine. Lipoic acid is a vitamin. NAD+ comes from B vitamin niacin. FAD comes from B vitamin riboflavin.
Why is the reaction catalyzed by citrate synthesis considered a condensation reaction?
A condensation reaction is one in which a new carbon-carbon bond is formed. The reaction of acetyl-CoA and oxaloacetate to produces citrate involves formation of such a carbon-carbon bond.
In which step of the aerobic processing of pyruvate is CO2 produced?
Conversion of pyruvate to acetyl-CoA, conversion of isocitrate to alpha-ketoglutarate, and conversion of alpha- ketoglutarate to succinyl-CoA
What type of reaction is catalyzed by isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase?
These enzymes catalyze oxidative decarboxylation
What are the similarities and differences between the reactions catalyzed by pyruvate dehydrogenase and alpha- ketoglutarate?
The reactions proceed by the same mechanism and use the same cofactors. The differences is the initial substrate, pyruvate or alpha-ketoglutarate. During the course of the reaction, pyruvate dehydrogenase shuttles an acetyl unit through the reaction while
Which steps of aerobic metabolism of pyruvate through the citric acid cycle are control points?
The reactions are catalyzed by pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase
Describe multiple ways that PDH is controled?
PDH is controlled allosterically. It is inhibited by ATP, acetyl-CoA, and NADH. In addition it is subject to control by phosphorylation. When PDH kinase phosphorylates PDH, it becomes inactive. Removing the phosphate with the PDH phosphatase reactivates i
What are the two most common inhibitors of steps in the citric acid cycle and the reaction catalyzed by pyruvate dehyrdogenase?
ATP and NADH are the two most common inhibitors
How does an increase in the ADP/ATP ratio affect the activity of isocitrate dehydrogenase?
If the amount of ADP increase relative to ATP the cell needs energy(ATP) This situation not only favors the reactions of the citric acid cycle, which release energy, activating isocitrate dehydrogenase, but also stimulates the formation of NADH and FADH2
How does an increase in the NADH/NAD+ ratio affect the activity of pyruvate dehydrogenase?
If the amount of NADH in a cell increases relative to the amount of NAD+ the cell has completed a number of energy releasing reactions. There is less need for the citric acid cycle to be active; as a result' the activity of pyruvate dehydrogenase is decre
Would you expect the citric acid cycle to be more or less active when a cell has a high ATP/ADP ratio and a high NADH/NAD+ ratio?
The citric acid cycle is less active when a cell has high ATP/ADP ratio and high NADH/NAD+ ratio. Both ratios indicate a high energy charge in the cell indicating less of a need for the energy releaing reactions of the citric acid cycle
What would you expect a delta G of hydrolysis of a thioester to be?
Thioesters are high energy compounds that play a role in group transfer reactions. Their delta G of hydrolysis is large and negative to provide energy for the reaction
Why are Acetyl-CoA and succinyl-CoA, both high energy thioesters, chemical energies put to different uses?
The energy released by hydrolysis of acetyl-CoA is needed for the condensation reaction that links acetyl moiety to oxaloacetate, yielding citrate. The energy released by hydrolysis of succinyl-CoA drives the phosphorylation of GDP, yielding GTP
Some reactions of the citric acid cycle are endergonic. Explain how the overall cycle is exergonic.
The sum of the energies of the individual reactions is -44.3kJ for each mole of acetyl-CoA that enters the cycle
Which enzymes of the citric acid cycle are missing from the glyoxylate cycle?
isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and succinyl-CoA synthetase
What are the unique reactions of the glyoxylate cycle?
The conversion of isocitrate to succinate and glyoxylate catalyzed by isocitrate lyase and the conversion of glyoxylate and acetyl-CoA to malate catalyzed by malate synthase
Why is it possible for bacteria to survive on acetic acid as a sole carbon source, but not human beings?
Bacteria that have a glyoxylate cycle can convert the acetic acid to amino acids, carbohydrates, and lipids. Humans can only use the acetic acid as an energy source or to make lipids
Describe the various purposes of the citric acid cycle?
The citric acid cycle is central metabolic pathway and indirect producer of energy. It receives fuels from the other pathways at many points and generates reduced electron carriers that go into the electron transport chain. It is also involved in anabolis
Discuss oxidative decarboxylation.
the molecule that is oxidized loses a carboxyl group as a carbon dioxide. Examples are conversion of pyruvate to acetyl-CoA, isocitrate to alpha ketoglutarate, and alpha ketoglutarate to succinyl-CoA
Why is acetyl-CoA considered the contral molecule of metabolism?
Many compounds can form from acetyl-CoA, such as fats, carbohydrates, and many amino acids. Acetyl-CoA can also form fats and ketone bodies, as well as feed directly into the citric acid cycle