Citric Acid Cycle (Kreb Cycle)

**Why is it called Citric Acid Cycle?**

Because the first molecule that forms during the cycle's reactions is citrate, or citric acid in its protonated form.

**Where does the Citric Acid Cycle happen?**

8 enzyme-catalyzed reactions (of which 7 happen in the mitochondrial matrix while 1 happens in the matrix side of the inner mitochondrial membrane).

**How many enzymes are catalyzed in the Citric Acid Cycle?** 

8 enzyme-catalyzed reactions

**How many steps in the Citric Acid Cycle?**

8 steps

**What is substrate-level phosphorylation?** 

* ATP is formed directly in an enzyme-catalyzed reaction


* ADP attaches to an enzyme along with a phosphate-containing compound  i.e. PEP (phosphoenolpyruvate) or GTP (guanosine triphosphate)
* PEP/GTP transfers a phosphate group to ADP, forming ATP
* Occurs in glycolysis (stage 1) and Krebs cycle (stage 3)

**What is Oxidative Phosphorylation?**

* ATP is formed indirectly 


* Sequential redox reactions 
* Oxygen is the final electron acceptor 
* More complex 
* Yield more ATP than SLP (Substrate level phosphorylation)

**How many ATPs are generated from how many NADH and FADH2?**

1 ATP molecule from one acetyl coenzyme A molecule. Also produced are 3 NADH molecules and 1 FADH₂ molecule during the conversion of the acetyl-CoA to CO₂

**Can you distinguish between citrate and isocitrate?** 

The positioning of the hydroxyl group.

**How many carboxyl groups in citrate and isocitrate?**

Both groups have 3 carboxyl groups.

**What are the carbons released as in the Citric Acid Cycle?** 

Two carbons—from acetyl CoAstart text, C, o, A, end text—enter the citric acid cycle in each turn, and two carbon dioxide molecules are release

**Number of carbons in the molecules entering the Citric Acid Cycle**

3 carbons begin in the molecule

**How many carbons are left when it goes back to the start of the process using Oxaloacetate.** 

4 carbons left in the molecule.

How many carbon dioxide molecules are released?

Two CO₂