About Cellular Respiration ....

Cellular Respiration


We all need energy to function and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP). ATP, a high energy molecule, is expended by working cells. Cellular respiration occurs in both eukaryotic and prokaryotic cells. It has three main stages: glycolysis, the citric acid cycle, and electron transport.

 Glycolysis:


 Glycolysis literally means "splitting sugars." Glucose, a six carbon sugar, is split into two molecules of a three carbon sugar. In the process, two molecules of ATP, two molecules of pyruvic acid and two "high energy" electron carrying molecules of NADH are produced. Glycolysis can occur with or without oxygen. In the presence of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP. This process is called fermentation.

The Citric Acid Cycle:

The Citric Acid Cycle or Krebs Cycle begins after the two molecules of the three carbon sugar produced in glycolysis are converted to a slightly different compound (acetyl CoA). Through a series of intermediate steps, several compounds capable of storing "high energy" electrons are produced along with two ATP molecules. These compounds, known as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), are reduced in the process. These reduced forms carry the "high energy" electrons to the next stage. The Citric Acid Cycle occurs only when oxygen is present but it doesn't use oxygen directly.

Electron Transport:

Electron Transport requires oxygen directly. The electron transport "chain" is a series of electron carriers in the membrane of the mitochondria in eukaryotic cells. Through a series of reactions, the "high energy" electrons are passed to oxygen. In the process, a gradient is formed, and ultimately ATP is produced.

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