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## May 24 Krebs Cycle

This is also known as the Citric Acid Cycle, but I will be referring to it as the Krebs Cycle for the rest of the post. This occurs in the inner compartment, the matrix, of the mitochondria.

# Preparation for the Krebs Cycle

Before the Krebs Cycle begins, glycolysis occurred, and glucose turned into two pyruvate molecules. This also produced 2 net ATPs (used 2, generated 4), and 2 NADHs.

In order to be ready for the Krebs Cycle, the pyruvate has to be oxidized.

Openstax College, Biology

So, from that, an NAD+ is reduced to NADH, carbon dioxide is released,  and the pyruvate molecule becomes acetyl CoA. Now, we are ready for the Krebs Cycle.

# Krebs Cycle

Note that Acetyl CoA is a two carbon compound (backbone has two carbons, Acetyl CoA has 23 carbons). Acetyl CoA merges with Oxaloacetic Acid, which is a four carbon compound, to form Citric Acid, which is a six carbon molecule.

This is a screenshot from Khan Academy's video about the Krebs cycle. It's very good, you should look it up

## Process

First, the Citric Acid rearranges itself twice, before reducing a NAD+ to an NADH. Note: Khanacademy's diagram is order is out of order. Right after that, a CO2 is released, changing the molecule to a five-carbon compound. The molecule then reduces another NAD+ and releases a CO2. After that, a GDP is turned into a GTP, (Guanosine Triphosphate- very similar to ATP), but for now, we can just say it makes an ATP. Finally,  it reduces an FAD to an FADH2, and reduces an NAD+ to an NADH.

## Recap

Recall that the aforementioned process happens to each of the two pyruvates.

1 in the preparation phase, and 3 in the Krebs cycle.
1 + 3 = 4 NADH x 2 (4 per pyruvate) = 8 NADH + 2 NADH (from glycolysis) = 10 NADH total

### ATP

1 ATP in each = 2 ATP + 2 ATP (from glycolysis) = 4 ATP total