Citric Acid Cycle Overview

Citric Acid Cycle Overview

• The citric acid cycle, also known as the Krebs cycle or the tricarboxylic acid cycle, is an eight-step pathway requiring eight separate enzymes.
• This cycle takes place in the mitochondrial matrix of eukaryotic cells.
• The cycle is responsible for generating energy in the form of ATP, NADH, and FADH2.
• The cycle is a key part of aerobic respiration, which is the primary way that organisms generate energy from food.
• The cycle begins with acetyl-CoA, produced from the breakdown of glucose in glycolysis.

Steps of the Citric Acid Cycle

• Step 1: Citrate Synthase: Acetyl-CoA combines with oxaloacetate to form citrate.
• Step 2: Aconitase: Citrate is converted to isocitrate.
• Step 3: Isocitrate Dehydrogenase: Isocitrate is oxidized and decarboxylated to form alpha-ketoglutarate.
• Step 4: Alpha-Ketoglutarate Dehydrogenase: Alpha-ketoglutarate is oxidized and decarboxylated to form succinyl-CoA.
• Step 5: Succinyl-CoA Synthetase: Succinyl-CoA is converted to succinate, generating one GTP molecule.
• Step 6: Succinate Dehydrogenase: Succinate is oxidized to fumarate, generating FADH2.
• Step 7: Fumarase: Fumarate is hydrated to form malate.
• Step 8: Malate Dehydrogenase: Malate is oxidized to oxaloacetate, regenerating the starting molecule for the cycle.

Energy Yield from the Citric Acid Cycle

• For every acetyl-CoA that enters the cycle, the following molecules are produced: three NADH, one FADH2, and one ATP.
• Since one glucose molecule produces two pyruvate molecules in glycolysis, and therefore two acetyl-CoA molecules, the total yield per glucose molecule is doubled.

Importance of the Citric Acid Cycle

• The citric acid cycle is an essential pathway for cellular respiration, providing the majority of the ATP produced in aerobic respiration.
• The cycle also provides intermediates for other important metabolic pathways, such as amino acid synthesis and gluconeogenesis.
• The citric acid cycle is a critical part of the evolution of multicellular organisms, as it allows for more efficient energy production compared to anaerobic respiration.

This quiz covers the critical steps and functions of the citric acid cycle, also known as the Krebs cycle. You will learn about the enzymes involved and the energy products generated during this essential metabolic pathway. Test your understanding of how this cycle contributes to aerobic respiration.