INTERACTIVE PATHWAY · TWO CONNECTED STORIES
MTHFR, the citric acid cycle & ATP
Choose a stop to see what it does. Follow the folate side, then the energy side. The connection is ATP used to make SAM.
Explore a connection
Follow the whole story The citric acid cycle loads energy carriers. The respiratory chain helps make ATP. A separate methylation step spends some ATP to make SAM.
STORY 1 · FOLATE & METHYLATION
Prepare a methyl group. Use ATP.
MTHFR and MTR act in folate and homocysteine recycling. These are not steps of the citric acid cycle.
- What happens here?
The MTHFR enzyme helps change 5,10-methylene-THF into 5-MTHF. It uses a vitamin B2-derived helper called FAD. Think of this as preparing a methyl group for the next step. It is not a step in the citric acid cycle.
The bridge between stories Energy metabolism supplies ATP. The cell spends ATP to make SAM from methionine. Mitochondria also use methyl groups for some upkeep jobs. Those connections do not mean MTHFR directly runs the citric acid cycle.
STORY 2 · MITOCHONDRIAL ENERGY
From fuel to usable ATP
Tap each stage. Open a stop in the cycle to see what is passed along.
One turn, eight stops
Acetyl-CoA enters. NADH, FADH₂ and a small amount of GTP or ATP carry energy out. The cycle returns to its starting helper.
Oxaloacetate is ready for another acetyl-CoA. Energy carriers travel onward.
