Krebs

Question 1

The Krebs cycle is also known as the ____ cycle

Answer 1

Citric acid

Question 2

Where does the Krebs cycle take place?

Answer 2

In the mitochondrial matrix

Question 3

What does the Krebs cycle generate?

Answer 3

CO2, and the electron carriers NADH and FADH2, as well as ATP by substrate level phosphorylation

Question 4

The Krebs cycle is a ______ process by which the initial components are completely oxidized to ___, and the maximum energy found is transferred to….

Answer 4

1) continous

2) CO2

3) high energy electron carriers

Question 5

What is step 1 of the Krebs cycle?

Answer 5

Condensation: The acetyl group gained during the oxidation of pyruvate is released from CoA to the oxaloacetate, to form citrate by the enzyme citrate synthase.

Question 6

What are steps 2-3 of the Krebs cycle?

Answer 6

Isomerization: Citrate is transformed to isocitrate in two distinct steps by enzyme aconitase

Question 7

What is step 4 in the Krebs cycle?

Answer 7

First oxidation: Isocitrate dehydrogenase oxidizes isocitrate to alpha-ketoglutarate. In this process, the molecule is decarboxylated, allowing for the release of a CO2. NAD+ is reduced to NADH, where the energy from the redox rxn drives the decarboxylation rxn

Question 8

What is step 5 of the Krebs cycle?

Answer 8

Second oxidation: alpha-ketogluterate dehydrogenase oxidizes alpha-ketogluterate yielding NADH and removing CO2. The resulting molecule, succinate, is linked to CoA. Energy from the redox rxn drives the decarboxylation and the binding to CoA.

Question 9

What is step 6 of the Krebs cycle?

Answer 9

Substrate level Phosphorylation: The bond between succinate and CoA is high energy, when it is broken by succinyl-CoA synthetase, to form succinate,the energy released is used to form GTP (guanosine triphosphate). GTP can then transfer a phosphate to ATP via substrate level phosphorylation.

Question 10

What is step 7 of the Krebs cycle?

Answer 10

Third oxidation: Succinate is oxidized by succinate dehydrogenase, yielding fumerate and FADH2 from FAD

Question 11

What is FAD?

Answer 11

FAD is a coenzyme that is used as an electron carriers, similar to NAD+

Question 12

What is the main difference between NAD and FAD?

Answer 12

The electrons carried by FAD/FADH2 will yield less ATP than the one carried by NAD+/NADH

Question 13

True or false?

FAD/FADH2 is free to diffuse throughout the cell.

Answer 13

False, it must remain in the mitochondrion

Question 14

What is step 8 of the Krebs cycle?

Answer 14

Fourth oxidation and regeneration of oxaloacetate: First. water molecule is added to fumerate by the enzyme fumerase, creating malate

Question 15

What is step 9 of the Krebs cycle?

Answer 15

Fourth oxidation and regeneration of oxaloacetate: Malate is oxidized to oxaloacetate by the enzyme malate dehydrogenase. An NADH is yielded in the process. The oxaloacetate is then free to restart the Krebs cycle.

Question 16

For each acetyl CoA molecule, the Krebs cycle generates:

Answer 16

-1 ATP (substrate level phosphorylation)

-3 NADH & 1 FADH2 (those electron carriers (also H) will generate ATP in the oxidative phosphorylation)

• 2 CO2 (decarboxylation)

Question 17

Since one glucose produces 2 acetyl CoAs, the yield are _____ if we are considering the products for one glucose molecule.

Answer 17

Doubled

Question 18

All 6 carbons from glucose have been transformed to 6 ___ molecules.

Answer 18

CO2

Question 19

The energy from glucose can be found in the form of:

Answer 19

-2 FADH2 (from Krebs cycle)

-10 NADH (2 from glycolysis, 2 from oxidation of pyruvate to acetyl CoA, 6 from Krebs cycle)

-4 ATP (2 from glycolysis, 2 from Krebs cycle)