Ch 13: Citric Acid Cycle

What compound enters TCA?

Acetyl-CoA

What are the three stages of cellular respiration?

1. Carbon (e.g. pyruvate) incorporated into acetyl-CoA

2. Citric acid cycle oxidized acetyl-CoA

   • Produces CO₂, reduced e- carriers, small amount of ATP

3. Reduced e- carriers re-oxidized, provide E for ATP synthesis

In the citric acid cycle, how many CO₂ are produced for each pyruvate?

3

Where do the three stages of cellular respiration take place in an Eukaryotic cell?

The mitochondria

What main cellular respiration/metabolic processes occur in the inner membrane of the mitochondria, the matrix of the mitochondria, and the cytosol?

Inner membrane:

• ETC

Matrix:

• Pyruvate dehydrogenase complex

• TCA

• Fatty acid β-oxidation

Cytosol:

• Glycolysis

What are the products of one turn of the citric acid cycle (NOT including pyruvate dehydrogenase)?

• 2 CO₂

• 3 NADH

• 1 FADH₂

• 1 ATP/GTP

Which 3 steps in the citric acid cycle are used in regulation and why?

• Citrate synthase

• Isocitrate dehydrogenase

• α-ketoglutarate dehydrogenase

B/c these steps are irreversible.

Which reaction drives the citric acid cycle forwards due to its low delta G?

Acetyl-CoA + oxaloacetate → Citrate

What compound inhibits all 3 irreversible steps in the citric acid cycle?

NADH

What is an anaplerotic rxn?

Rxn that replenishes the components of the cycle.

What are the three subunits in the pyruvate dehydrogenase complex?

• E1 - pyruvate dehydrogenase

• E2 - dihydrolipoamide acetyltransferase

• E3 - dihydrolipoamide dehydrogenase

What is the role of the E2 and E3 subunits in the PDH complex?

They transfer electrons to electron carriers to reset the mechanism.

How is pyruvate dehydrogenase regulated? When does this regulation occur?

Phosphorylation of the E1 protein renders the subunit inactive.

When there is a high level of ATP, it drives the phosphorylation. Therefore, the pyruvate dehydrogenase does not occur.

In which turn of the citric acid cycle does it becomes possible to lose the carbons that were added from acetyl-CoA?

2nd turn of the cycle.

Which compound can be used for both the TCA cycle and gluconeogenisis?

Oxaloacetate

Which enzyme catalyzes the only substrate-level-phosphorylation rxn in the TCA cycle?

Succinyl-CoA

Why do we need to transfer electrons from the TCA cycle from FADH₂ to QH₂?

B/c FADH₂ is bound to enzyme. Transferring the electrons to QH₂ allows it do diffuse away from the enzyme through the membrane.

The last step in the TCA cycle, the formation of oxaloacetate, has a very positive delta G. Why is this reaction still favorable?

B/c there is a very low concentration of oxaloacetate as it gets pulled into a super favorable next reaction.

At _____ concentrations of ATP, oxaloacetate replenishes the TCA cycle as opposed to being converted to glucose.

Low

What is the total amount of ATP molecules generated from one glucose molecule?

30 - 32 ATP

Which mechanism for transporting NADH from glycolysis into the mitochondria generates more ATP?

Transferring the e- from NADH into malate which then crosses and transfers the carried e- onto a new NAD+ located inside the mitochondria.