The glyoxylate cycle, pronounced /ɡlaɪˈɑksəleɪt ˈsaɪkəl/, is a metabolic pathway found in plants, bacteria, and fungi. It allows organisms to convert acetyl-CoA into carbohydrates, which can then be used for energy or building biomass. The spelling of the word "glyoxylate" follows the common English pronunciation rules for the letters "g," "y," and "x," while "cycle" is spelled phonetically as it would be pronounced in English. Phonetic transcription helps explain the correct pronunciation of complex scientific terms like the glyoxylate cycle.
The glyoxylate cycle, also known as the glyoxylate shunt, is a metabolic pathway found in certain organisms, including bacteria, algae, fungi, and plants. It is an alternative pathway to the tricarboxylic acid (TCA) cycle, also referred to as the citric acid cycle or Krebs cycle.
The glyoxylate cycle enables these organisms to utilize two-carbon compounds, such as acetate or fatty acids, as a source of carbon and energy. In comparison, the TCA cycle is unable to directly metabolize these two-carbon compounds.
In the glyoxylate cycle, the two-carbon compound is first converted into isocitrate, bypassing the initial steps of the TCA cycle. The enzyme isocitrate lyase facilitates this conversion, breaking down isocitrate into glyoxylate and succinate. Glyoxylate is then further metabolized, undergoing a series of reactions that regenerate the initial four-carbon intermediate, thereby enabling the cycle to continue.
As a result, the glyoxylate cycle allows the organism to produce intermediates required for biosynthesis, mainly carbohydrates, from acetate or fatty acids. This ability is especially significant during conditions of carbon limitation, such as when the organism is growing on fatty acids as the primary carbon source.
Overall, the glyoxylate cycle plays a crucial role in the metabolism of certain organisms, allowing them to efficiently utilize two-carbon compounds for growth and survival.
The etymology of the word "glyoxylate cycle" can be broken down as follows:
1. Glyoxylate: The term "glyoxylate" is derived from two Greek words: "glykys", meaning sweet, and "oxys", meaning sharp or acid. Therefore, "glyoxylate" can be understood as an acid derived from a sugar.
2. Cycle: In this context, "cycle" refers to a series of chemical reactions that continuously occur and regenerate the starting compound. It comes from the Greek word "kyklos", meaning circle or wheel, indicating a recurring pattern.
Combining these components, the term "glyoxylate cycle" refers to the recurring series of reactions involving the conversion of glyoxylate and related compounds within a biological system, typically found in certain organisms like plants and bacteria.