Biochemistry TCA cycle intermediates flashcards

What is the TCA cycle?

The TCA cycle, or Krebs cycle, is a series of enzyme-catalyzed chemical reactions that are central to cellular respiration. It generates energy through the oxidation of acetyl-CoA.

Key purpose of the TCA cycle?

To generate ATP, NADH, and FADH₂ through the oxidation of carbohydrates, fats, and proteins.

True or False: The TCA cycle occurs in the cytoplasm.

False. The TCA cycle occurs in the mitochondrial matrix of eukaryotic cells.

How many ATP are produced per turn?

1 ATP (or GTP) is produced per cycle turn.

Which molecule enters the TCA cycle?

Acetyl-CoA enters the TCA cycle, derived from carbohydrates, fats, and proteins.

Fill in the blank: The TCA cycle is also known as the _____ cycle.

Krebs cycle.

Identify two key products of the TCA cycle.

1. NADH 2. FADH₂

Cause → Effect: Increased NADH levels lead to _____?

Inhibition of the TCA cycle due to feedback regulation.

What intermediate connects glycolysis and the TCA cycle?

Pyruvate is converted to acetyl-CoA, linking glycolysis to the TCA cycle.

True or False: The TCA cycle operates only in aerobic conditions.

True. The TCA cycle requires oxygen indirectly through NADH and FADH₂ oxidation.

Compare citrate and alpha-ketoglutarate.

Citrate is the first intermediate; alpha-ketoglutarate is produced after two decarboxylations.

Which enzyme catalyzes the first step?

Citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate.

What is the role of succinate?

Succinate is an intermediate that gets oxidized to fumarate, producing FADH₂.

How many carbons are in oxaloacetate?

Oxaloacetate has 4 carbons.

Fill in the blank: Fumarate is converted to _____ in the TCA cycle.

Malate.

What is the final product of the TCA cycle?

Oxaloacetate regenerates to continue the cycle, completing the process.

Acetyl-CoA → definition?

Acetyl-CoA is a 2-carbon molecule formed from the breakdown of carbohydrates, fats, and proteins. It enters the TCA cycle, combining with oxaloacetate.

What is citrate's role?

Citrate is formed when acetyl-CoA combines with oxaloacetate. It is the first intermediate in the TCA cycle, initiating the cycle.

Isocitrate: true or false?

True. Isocitrate is derived from citrate through an enzymatic rearrangement.

Isocitrate → α-ketoglutarate. What happens?

Isocitrate undergoes oxidative decarboxylation, losing CO₂ and reducing NAD⁺ to NADH, producing α-ketoglutarate.

α-Ketoglutarate → main features?

α-Ketoglutarate is a 5-carbon intermediate that further undergoes oxidative decarboxylation to form succinyl-CoA, generating NADH.

Succinyl-CoA → definition?

Succinyl-CoA is produced from α-ketoglutarate. It is a 4-carbon compound that can produce ATP in the next step of the cycle.

Compare succinate and fumarate.

Both are 4-carbon intermediates, but succinate is a product of succinyl-CoA and fumarate is formed from succinate via oxidation.

Fumarate → malate: how does it happen?

Fumarate is converted to malate through hydration, adding a water molecule.

Malate: what is its significance?

Malate is the final 4-carbon intermediate before regeneration of oxaloacetate. It is oxidized to produce NADH.

What is the final product of malate oxidation?

The oxidation of malate results in the regeneration of oxaloacetate, while reducing NAD⁺ to NADH.

True or False: Oxaloacetate can be synthesized?

True. Oxaloacetate can be synthesized from pyruvate and various amino acids, maintaining TCA cycle function.

Identify this intermediate: C6H5O7.

This compound is citrate, a key player in the TCA cycle.

Cause: α-ketoglutarate → succinyl-CoA. Effect?

This step produces CO₂ and NADH, vital for energy production.

Fill in the blank: Succinyl-CoA → ____ + ATP.

Succinyl-CoA → succinate + ATP. This step is a substrate-level phosphorylation.

What happens during the conversion of succinate to fumarate?

Succinate is oxidized by succinate dehydrogenase, producing fumarate and FADH₂.