citric acid cycle Flashcards
what are other names of the citric acid cycle
tricarboxylic acid cycle- krebs cycle
what happens when you add acetyl coa to the citric acid cycle
two carbons are inputted and so outputted and intermediate molecule is re formed
what are sources of acetyl coa
fatty acids- acetyl coa (beta oxidation), fasting and excerise
ketogenic amino acids- acetyl coa (different catabolic pathways, fed and some stages of fasting/starvation
ketogenic amino acids do not increase gluconeogenesis
in what stage are sugars converted to pyruvate
glycolysis
what enzyme converts pyruvate into acetyl coa
pyruvate dehydrogenase
what is pyruvate dehydrogenase
pyruvate from glycolysis is the source of acetyl coa used for fatty acid synthesis
what does pyruvate dehydrogenase convert 3 carbon pyruvate into
2 carbon acetyl coa which can be used for fatty acid synthesis
how is pyruvate dehydrogenase regulated and inhibited
by its products
how is pyruvate dehydrogenase stimulated
by its substrates
its also responsive to energy charge of the cell
is the pyruvate to acetyl coa reaction reversible
it is irreversible
destroys gluconeogenic potential of the pyruvate in mammals 2c compounds cannot be converted into glucose therefore in the liver, only activated when glucose is plentiful
pyruvate has four destinations what are they
alanine lactate oxaloacetate acetyl coa
what is beri beri thiamine deficiency
thiamine is needed to make cofactor of pyruvate dehydrogenase
metabolism of pyruvate very important for nerve cells so the nervous system is strongly affected e,g tingling and confusion
dietry changes (switching from brown to white rice) can lead to deficiency and some food contains thiaminases
infantile beri beri seen in breast fed babies of affected mothers at 2-3 months. death may occur within minutes of onset of shock of respiratory distress
thiamine injection can lead to recovery within 6 hours
what is pyruvate dehydrogenase deficiency
typically diagnosed in infancy delayed development reduced muscle tone, often with seizures
all patients with pdh deficiency have some form of neurological impairment. this is because the brain normally obtains all of its energy from the aerobic oxidation of glucose.
foetuses have poor weight gain towards the end of the pregnancy due to lack of fatty acid synthesis
because pyruvate cant enter the CAC it is converted to lactate
the elevated levels of pyruvate and lactate inthe plasma
treatment- a ketogenic diet 15% protein, 5% carbohydrate this ensures that cells use acetyl coa from fat metabolism
how does acetyl coa enter the citric acid cycle
through addition to oxaloacetate two carbons are lost as co2 and oxaloactetate is reformed
nadh fadh2 gtp atp are produced
what three enzymes are involved in regulating the citric acid cycle
citrate synthase
isocitrate synthase
alpha- ketoglutarate dehydrogenase
to continue citric acid cycle, what do the intermediates need to be replaced by
anaplerotic reactions
what are anaplerotic reactions
reactions in which compounds are converted into intermediates of the citric acid cycle
fat synthesis- replaces citrate
gluconeogenesis-part of converting pyruvate to phosphoenolpyruvate
excersise increased rate of CAC
makes 1 intermediate
the c skeleton can be used for gluconeogenesis
feeds nitrogenous waste into urea cycle
what does excess citrate involve
if the acetyl coa supply is more than the citric acid enzymes can cope with, citrates are released and can enter cytosol
in the liver or adipose this will be used to stimulate fatty acid synthesis
in muscle this would inhibit glycolysis and or fatty acid oxidation as the acetyl coa supply is sufficient
what does inadequate oxaloacetate cause
in the liver, oxaloacetate is low because intermediates are being drawn off for gluconeogenesis during fasting state, acetyl coA cannot enter the cac at all and so is used for ketogenesis instead
citric acid cycle occurs in all mitochondria
if the cell is using more energy then it is more active during excerise
to increase the activity
increase activity of enzymes
increase supply of acetyl coA
increase concentration of intermediates
