The TCA Cycle Flashcards
Where does the TCA cycle happen?
- Everywhere and in all tissues requiring energy in the fed state
- Except RBC because there are no mitochondria
What is the common end product of carbohydrate, fatty acid and amino acid metabolism?
Acetyl CoA
What is acetyl CoA used for the biosynthesis of in the cytoplasm?
- Fatty acids
- Ketone bodies (only in the liver)
- Cholesterol
Where can it be stored for use in the TCA cycle and why?
- Mitochondrial matrix
- Too big to cross inner mitochondrial matrix
What is acetyl CoA converted to in the TCA cycle (step 1)?
- Citrate (6 carbons)
- Combines with oxaloacetate
- Condensation reaction
- Citrate synthase
What is released in step 1 of TCA cycle?
- Water
- CoA
What is citrate converted to in TCA cycle (step 2)?
- Isocitrate (6 carbons)
- Slight modification of the structure
What is isocitrate converted to in TCA cycle (step 3)?
- α-ketoglutarate
- 5 carbon molecule
- Enzyme: isocitrate dehydrogenase
What is released in step 3 of TCA cycle (isocitrate–> α-ketoglutarate)?
- NADH (reduced from NAD+)
- One carbon dioxide molecule
What inhibits isocitrate dehydrogenase?
- High levels of NADH or ATP in the cell
- Slows down turning of TCA cycle
- When active it donates electrons from isocitrate to NAD
What is α-ketoglutarate converted to in TCA cycle (step 4)?
- Succinyl CoA
- 4 carbon molecule
- CoA temporarily re-introduced
- Enzyme: α-ketoglutarate dehydrogenase
What is released in step 4 of the TCA cycle (α-ketoglutarate –> succinyl CoA)?
- NADH (reduced from NAD)
- Carbon dioxide molecule
What is succinyl CoA converted to in TCA cycle (step 5)?
- Succinate
- CoA quickly lost
- No enzyme
What is released in step 5 of the TCA cycle (succinyl CoA–> succinate)?
- CoA
- GTP (GDP + Pi)
What is succinate converted to in TCA cycle (step 6)?
- Fumarate
- 4 carbon molecule
- Enzyme: succinate dehydrogenase
What is released in step 6 of the TCA cycle (succinate to fumarate)?
- FADH (reduced from FAD)
What is fumarate converted to in TCA cycle (step 7)?
- Malate- 4 carbons
- Enzyme: Fumarase
- Fumarate + water
What is malate converted to in the TCA cycle (step 8)?
- Oxaloacetate
- 4 carbon
- Enzyme: malate dehydrogenase
What is released in step 8 of TCA cycle (malate to oxaloacetae)?
- NADH (Reduced from NAD+)
What happens to all the NADH/FADH molecules released from TCA cycle?
- Become electron donors in the electron transport chain
- One molecule of FADH2
- 3 molecules of NADH (each accepting 2 electrons)
What are the two major flavin redox coenzymes?
- Flavin adenine dinucleotide (FAD)
- Flavin mononucleotide (FMN)
How many electrons and protons do FAD and FMN accept?
- 2 electrons
- 2 protons
- For molecules undergoing metabolism
What vitamin do FAD and FMN both contain
- Riboflavin-5’-phosphate
- Produced from vitamin B2 (riboflavin)
What is meant by ‘anaplerotic reactions’?
- Filling up reactions
- Intermediates of the TCA cycle solely for use of the TCA cycle
What other reactions is oxaloacetate used for?
- Amino acids synthesis (non-essential ones as they can be formed in the body)
What other reactions is α-ketoglutarate used for?
- Amino acid synthesis
- Neurotransmitter synthesis in the brain
What other reaction is malate used for?
- Gluconeogenesis
What other reaction is succinyl CoA used for?
- Haem synthesis
What other reaction is citrate used for?
- Fatty acid synthesis
What are glucogenic and ketogenic type amino acids?
- Able to join the TCA cycle at different points
- Amino acids can go into TCA cycle and help replenish intermediates- they can be converted to convenient molecules
What processes are glycogenic and ketogenic amino acids used for when removed from TCA cycle?
- Gluconeogenesis
- Ketogenesis (by forming acetyl CoA)
What does the ‘link reaction’ convert pyruvate into?
Acetyl CoA
How can pyruvate be directly inserted into the TCA cycle?
- Converted directly into oxaloacetate
- Requires some energy
- Pyruvate carboxylase is used for this reaction
Describe the structure of ATP?
- Adenine
- Ribose sugar
- 3 phosphate groups
Describe stage 1 of fuel oxidation
- Production of reduced nucleotide coenzymes during oxidation of fuels and the release of carbon dioxide
- Reduced enzymes include NADH and FADH2
Describe stage 2 of fuel oxidation
- When electron carriers are passing electrons into electron transport chain
- Oxygen required
- ATP generated from free energy provided by oxidation of reduced coenzymes
