The Krebs Cycle Made Easy

The Krebs cycle, also called the citric acid cycle or the tricarboxylic acid cycle, is a sequence of chemical reactions that convert glucose, proteins and fats into energy for living cells in the form of adenosine triphosphate, or ATP.

Living cells use the energy from ATP to synthesise proteins from amino acids and to replicate deoxyribonucleic acid, or DNA. The Krebs cycle is a complex process that is difficult to explain in everyday language, although people who are familiar with biological concepts may find it easier to understand.


The Krebs cycle occurs in the mitochondrial matrix of the living cells of aerobic organisms. Aerobic organisms are living organisms that require oxygen for growth and survival. Aerobic organisms include most animals as well as some fungi. The mitochondrial matrix is the space within the inner membrane of the mitochondrion that contains hundreds of enzymes that function as part of the Krebs cycle. The mitochondrion is an organelle, an organ of the cell itself, that functions as the "power plant" of the living cell since it creates most of the adenosine triphosphate necessary for cell energy.

Simplified Explanation

Glucose, a sugar molecule or carbohydrate, combines with oxygen to produce carbon dioxide, water and adenosine triphosphate (ATP). ATP is the energy necessary for the living cells to function, while carbon dioxide and water are the waste products of this chemical reaction. The first and final products of the Krebs cycle are citric acid, which breaks down and regenerates in the complex process of ATP synthesis.

Chemicals and Enzymes

A molecule called Acetyl-CoA combines with a chemical compound called oxaloacetate to create a citrate, or citric acid. The citric acid loses carbon dioxide from the oxaloacetate in the process of oxidation, and the electrons from this chemical reaction transfer to a coenzyme called nicotinamide adenine dinucleotide, or NAD+, to create NADH. The Acetyl CoA molecule produces three molecules of NADH. NADH is a reducing agent that transfers electrons to other atoms in the Krebs cycle such as the amino acid glutamine, or Q, to form QH2. The oxaloacetate regenerates in the fnal stage of the Krebs cycle, which again combines with Acetyl-CoA as another cycle begins and the living cell continues producing adenosine triphosphate.