TRICARBOXYLIC ACID CYCLE AND PYRUVATE DEHYDROGENASE COMPLEX Flashcards
- aerobic pathway
- final pathway where the oxidative catabolism of carbohydrates, amino acids, and fatty acids converge, their carbon skeletons being converted to CO2
- responsible for producing most of the energy that cells need to function
The tricarboxylic acid (TCA) cycle/ Citric acid cycle/ Kreb’s cycle
Functions: Krebs Cycle
Energy production:
Intermediates for biosynthesis
The cycle begins with the condensation of _____, which is derived from the breakdown of carbohydrates, amino acids, and fatty acids, with oxaloacetate to form citrate.
acetyl-CoA
____ is then converted to a series of other intermediates, including isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, and malate.
Citrate
____ is converted back to oxaloacetate to complete the cycle
malate
The cycle ends with the regeneration of ______, which can then be condensed with another molecule of acetyl-CoA to start the cycle again
oxaloacetate
The _____ catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA.
pyruvate dehydrogenase complex (PDH complex)
The PDH complex is located in the mitochondrial matrix and contains five coenzymes:
TPP, lipoic acid, CoA, FAD, and NAD+.
The PDH complex is regulated by two enzymes:
pyruvate dehydrogenase kinase (PDH kinase) and
pyruvate dehydrogenase phosphatase (PDH phosphatase).
PDH kinase phosphorylates the PDH complex, which ____ it.
inactivates
PDH phosphatase dephosphorylates the PDH complex, which ___it.
activates
____ is activated by high-energy signals, such as ATP, acetyl-CoA, and NADH.
PDH kinase
___ is an inhibitor of PDH kinase.
Pyruvate
___ activates PDH phosphatase
Calcium
can cause serious central nervous system problems.
brain cells are unable to produce sufficient ATP (via the TCA cycle) if the PDH complex is inactive.
Thiamine or niacin deficiency:
an encephalopathy -psychosis syndrome due to thiamine deficiency, may be seen with alcohol abuse
Wernicke-Korsakoff
is a rare genetic disorder that affects the way the body converts food into energy.
deficiency results in an inability to convert pyruvate to acetyl CoA
can cause a variety of symptoms, including developmental delays, muscle weakness, seizures, and intellectual disability.
Pyruvate dehydrogenase complex (PDH) deficiency
rare, progressive, neurodegenerative disorder caused by defects in mitochondrial ATP production
Leigh syndrome (subacute necrotizing encephalomyelopathy)
can interfere with glycolysis at the glyceraldehyde 3- phosphate step, thereby decreasing ATP production. this particularly affects the brain, causing neurologic disturbances and death.
inhibit enzymes that require lipoic acid as a coenzyme.
Arsenic poisoning
The condensation of acetyl CoA and oxaloacetate (OAA) to form citrate (a tricarboxylic acid) is catalyzed by ____
citrate synthase.
Citrate is isomerized to isocitrate by the enzyme ____ .
aconitase
___ catalyzes the oxidative decarboxylation of isocitrate to alphaketoglutarate.
Isocitrate dehydrogenase
The oxidative decarboxylation of α-ketoglutarate to succinyl CoA is catalyzed by the ___
α - ketoglutarate dehydrogenase complex.
Succinate is oxidized to fumarate by ___
succinate dehydrogenase.
Fumarate is hydrated to malate by _____.
fumarase
Malate is oxidized to oxaloacetate by ___
malate dehydrogenase.
When the ATP/ADP ratio is ___high, the TCA cycle is downregulated. This is because the cell has enough energy and does not need to produce more.
high
When the ATP/ADP ratio is ___, the TCA cycle is upregulated. This is because the cell needs more energy and needs to produce more.
low
