Lecture 9- Krebs Cycle Flashcards
What is the goal of the Krebs’ cycle? Where does it occur?
To extract energy from pyruvate, the remanent of glycolysis. It occurs in the mitochondrial matrix.
What does pyruvate need to do before entering the mitochondria?
Before entering the mitochondria, it needs to be reduced. This reduction of pyruvate oxidizes an NAD+ molecule into NADH.
How is pyruvate changed to enter the mitochondria, what are the products?
- Decarboxylation: a CO2 group is removed from pyruvate to create an acetyl group.
- An NADH molecule is produced.
- The acetyl group is transferred to coenzyme A to create Acetyl CoA.
The products are for each pyruvate are one Acetyl CoA, one CO2, and one NADH.
What is the bond between the acetyl group and coenzyme A?
The acetyl thioester bond.
Briefly describe the steps of the Krebs’ cycle.
- The Acetyl group bind to Oxaloacetate (created in the last step of the cycle).
2-3. Isomerization, product is isocitrate. - First oxidation, NADH is formed and isocitrate is decarboxylated, yielding one CO2 molecule and one NADH molecule.
- Second oxidation, one CO2 and one NADH are produced. The CoA enzyme binds to the product.
- CoA detaches from product, energy released is used to make GTP from GDP and P. This is called substrate-level phosphorylation.
- Product is once more oxidized, this time making FADH2.
8-9. Oxaloacetate is regenerated by the addition of H2O and an oxidation, generating another NADH molecule.
What are the products of the Krebs’ cycle for one molecule of glucose (2 Acetyl CoA molecules)?
6 NADH molecules, 2 FADH2 molecule, 2 ATPs, and 4 CO2 molecules.
Where is the remaining energy from the original glucose located once it has gone through glycolysis and the Krebs’ cycle?
In the NADH and FADH2 molecules.
What are the differences between NADH and FADH2?
NADH contains more energy than FADH2. In addition to that, FADH2 must remain in the mitochondrion, as it cannot diffuse through the cell.
