M2: Cataplerotic and Anaplerotic Rxns L11 Flashcards
What are the cataplerotic reactions used for anabolism?
- Glucose biosynthesis
- Fatty acid biosynthesis
- Amino acid biosynthesis
What are the anaplerotic reactions used for catabolism?
- Formation of Oxaloacetate
- Formation of Malate
- Formation of A-Ketoglutarate
What are the different ways to form amino acids from the CAC intermediates? What type of reaction is it?
All cataplerotic/anabolism reactions
- Going from oxaloacetate to aspartate through transamination. Amino acids made from Aspartate.
- From alpha-ketoglutarate to glutamate by transamination. Amino acids made from Glutamate.
How do you get oxaloacetate out of the the mitochondria?
Oxaloacetate is not transported out of mitochondria on its own. It’s converted to malate or aspartate. Then aspartate or malate gets out of mitochondria into cytosol and turns back into oxaloacetate.
Oxaloactetate can also leave via citrate (carrier). Citrate will be broken down by ATP citrate lyase which will release oxaloacetate and acetyl-CoA
How do you get glucose biosynthesis? What type of reaction is it?
Phosphoenolpyruvate (PEP) can be converted to G6P to promote gluconeogenesis.
How do you make fatty acids from the CAC? What kind of reaction is it?
Reaction: Catapleurotic/Anabolic
Acetyl-CoA is in the citrate molecule. Citrate is the carrier to export it out of mitochondria. Once it leaves mitochondria, citrate can be broken down in cytosol by ATP citrate lyase. This regenerates Acetyl-CoA and oxaloacetate in the cytosol. The Acetyl-CoA goes on to make fatty acids. This is another route for oxaloacetate to get into the cytosol.
Why are anaplerotic reactions critical?
CAC cannot be interrupted, so intermediates drawn off MUST be replenished.
How is the pyruvate carboxylase reaction an anaplerotic reaction and why is it useful?
Rxn: Pyruvate + ATP to Oxaloacetate by pyruvate carboxylase which allows CAC to refill.
Pyruvate carboxylase senses the need to fill up CAC through its allosteric activator Acetly-CoA. If you have a decrease in CAC rate (ex: insufficient intermediates like oxaloacetate) it will cause AxetylCoA conc. to rise. AcetylCoA can then activate pyruvate carboxylase. This can regenerate and replenish all the CAC intermediates just by regenerating oxaloacetate.
What anaplerotic reactions stem from pyruvate?
- Pyruvate carboxylase rxn to generate oxaloacetate
- Transaminase rnx to generate Alanine and alpha-Ketoglutarate.
- Pyruvate + NADPH to Malate by Malic enzyme
How is the pyruvate transaminase reaction an anaplerotic reaction and why is it useful?
Rxn: Pyruvate to form Alanine and alpha-Ketoglutarate by a transaminase enzyme.
Pyruvate has the ability to accept an amino group from glutamate. This transamination rxn generates an alanine (pyruvate + amino group) and an a-ketoglutarate (glutamate - amino group). This refills CAC by dumping in a-ketoglutarate which initiates cycle and refills all intermediates.’
How is malate replenished and what type of reaction is it?
Rxn: Pyruvate to malate via malic enzyme. Consumes NADPH.
Anapleurotic/Catabolic rxn
What type of reaction is the aspartate transaminase reaction?
Can be anaplerotic or cataplerotic depending on the direction of the reaction:
Glutamate + Oxaloacetate REVERSIBLY TO alpha-ketoglutarate + Aspartate.
Describe the glutamate dehydrogenase reaction. Why is it favoured? What type of reaction is it?
Anapleurotic reaction: Glutamate to alpha-ketoglutarate via glutamate dehydrogenase. Makes an NADH.
Another way for glutamate to replenish the a-ketoglutarate pool. The rxn is reversible but it’s very unfavourable to go in the reverse direction. This is bc to go in reverse, ammonia (NH4+) needs to bind to glutamate dehydrogenase. But the Km for ammonia is rly high, so for the rxn to go from right to left, ammonia would have to build up to rly toxic levels. So in a living cell it would only go from L to R even though in theory it could be reversible.
