What Is the Primary Fuel for Cellular Respiration?

Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

Cellular respiration involves a few different steps and molecules to create energy for cells. One molecule in particular sparks the entire process. In this lesson, we'll discuss this molecule and some of its associated molecules.

What is Cellular Respiration?

Cellular respiration refers to a multi-step process that breaks down food and converts it to energy for an organism. You cannot just eat food and magically use the energy; it has to be processed. This is similar to drilling for oil - the oil must be processed for use in gasoline.

Most of the respiration process occurs in the mitochondria of the cell, but the initial stage starts in the cytoplasm and cytosol. Ultimately, the end product is adenosine triphosphate (ATP), which is the molecule that our bodies use as an energy source. Let's walk through a brief overview of the entire cellular respiration process.

Cellular respiration consists of a series of cycles and processes that occur almost simultaneously. The first is glycolysis, in which a molecule of glucose is broken down into four molecules of ATP and two pyruvate molecules. Two of the ATP molecules are absorbed and used in the next glycolysis process; the other two ATP molecules are products to be used by the cell and are counted in the overall energy production summary. The pyruvates are eventually prepared to become different energy molecules for use in the next cycle, which we'll discuss in just a moment.

Glycolysis: Notice that we start with glucose, then end up with two pyruvate molecules, two NADH, and two ATP.

At the same time, the citric acid cycle, otherwise known as the Krebs Cycle, is initiated. In this cycle, carbon dioxide and NADH (another energy molecule) are created. Finally, the oxidative phosphorylation phase occurs, which uses the NADH to produce water as a waste product. When cellular respiration is complete, 32 molecules of ATP are created in each cell. This may not seem like a lot, but if you picture all of the cells in the human body, most of which would be utilizing this process - that is a whole lot of energy being produced!

Primary Respiration Fuel

After reading the overview of cellular respiration, the primary or initial fuel of respiration should be clear - it's glucose, which is the molecule of sugar that plants create for animals (as well as the plant itself) to utilize as an energy source. Glucose is similar to the gasoline in your car engine - it fires the engine that is your body by breaking apart and releasing energy to get everything moving! It is comprised of six carbon, twelve hydrogen, and six oxygen atoms and kick-starts the entire cellular respiration process via glycolysis.

Glycolysis breaking glucose into two pyruvate molecules.
Glycolysis Again

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