Carbohydrates 5
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What are other names for the Citric acid cycle?
• Krebs cycle - Tricarboxylic acid cycle (TCA)
What fuel molecules go through the citric acid cycle?
All fuel molecules: • Carbohydrates • Fatty acids • Amino acids
Where does the citric acid cycle occur?
Mitochondrial matrix
What happens in the citric acid cycle?
-It removes e’s and passes them on to form NADH and FADH
Why is the citric acid cycle very efficient?
• Cyclical in nature - Small number of citric acid cycle molecules can make loads of NADH and FADH
How is acetyl CoA formed?
• Occurs in the mitochondrial matrix • Action of pyruvate dehydrogenase • Pyruvate undergoes decarboxylation, oxidation and transfer of CoA complex. • 2H are released during decarboxylation
What are role do each of the enzyme subunits of pyruvate dehydrogenase play?
• E1 catalyses the first decarboxylation of pyruvate • E2 transfers the acetyl group to coenzyme A • E3 recycles the lipoyllysine through the reduction of FAD which is recycled by passing electrons NAD
What happens each turn of the citric acid cycle?
2C’s enter as acetyl CoA and 2C’s are removed as CO2
What reaction is similar to pyruvate dehydrogenase?
a-ketoglutarate dehydrogenase
How is entry into the cycle controlled?
• Pyruvate dehydrogenase is regulated by it’s immediate products and the end point of cellular respiration ATP • Its regulated depending on the needs of the cell
What is the nature of the 2 points of control of the citric acid cycle?
They are non-reversible reactions (exergonic steps)
What are the 2 other points of control?
• Isocitrate dehydrogenase - a-ketoglutarate dehydrogenase
Describe isocitrate dehydrogenase.
• As with pyruvate dehydrogenase enzyme is allosterically controlled through ATP and NADH concentrations. • ATP and NADH will negatively r
Describe a-ketoglutarate dehydrogenase.
• ATP and NADH negatively regulate - Also succinyl CoA negatively regulates
How do the control points allows re-direction of cellular resources?
• Blocking isocitrate dehydrogenase causes citrate to build up which shuttle citrate into the cytoplasm causing phosphofructokinase to stop glycolysis • a-ketoglutaratenbuilds up when a-ketoglutarate dehydrogenase is inactive, which switches its use to production of amino acids
What happens when the cellular energy needs are met through the citric acid cycle?
It can produce the building blocks of nucleotide bases, haem groups and proteins
What can the enzyme pyruvate carboxylase do?
Can convert pyruvate to oxaloacetate
When is pyruvate carboxylase active?
It is only active when acetyl CoA is present so a build up of acetyl CoA triggers the reaction.