Plant Secondary Metabolism PDF
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Uploaded by EntrancedAstronomy
University of Babylon
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This document provides an overview of four important metabolic pathways in plants: Shikimate, Acetate-Malonate, Mevalonate, and Cholesterol. It details the precursors, products, and steps involved in each pathway, and explains how these pathways relate to the synthesis of various important compounds, including amino acids, fatty acids, terpenoids, and steroids.
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## Plant Secondary Metabolism ### Overview - **Metabolism:** The sum of all chemical processes that occur within a living organism in order to maintain life. - **Primary Metabolism:** Reactions directly involved in growth and development (e.g. photosynthesis, respiration) - **Secondary Metabolism:...
## Plant Secondary Metabolism ### Overview - **Metabolism:** The sum of all chemical processes that occur within a living organism in order to maintain life. - **Primary Metabolism:** Reactions directly involved in growth and development (e.g. photosynthesis, respiration) - **Secondary Metabolism:** Reactions that produce organic compounds not directly involved in growth (e.g. alkaloids, terpenoids) ### The Shikimate Pathway - **Precursors:** Erythrose 4-phosphate and phosphoenolpyruvate - **Products:** Aromatic amino acids (L-tryptophan, L-tyrosine, L-phenylalanine) - **Steps:** 1. Erythrose 4-phosphate + Phosphoenolpyruvate = 3-Deoxy-D-arabino-heptulosonate-7-phosphate 2. 3-Deoxy-D-arabino-heptulosonate-7-phosphate = 3-Dehydroquianate 3. 3-Dehydroquianate = 3-Dehydro shikimate 4. 3-Dehydro shikimate = Shikimate 5. Shikimate = Shikimate 3-phosphate 6. Shikimate 3-phosphate + Phosphoenolpyruvate = 5-Enolpyruvylshikimate 3-phosphate 7. 5-Enolpyruvylshikimate 3-phosphate = Chorismate ### The Acetate - Malonate Pathway - **Precursors:** Acetyl-CoA and Malonyl-CoA - **Products:** Fatty acids - **Steps:** 1. Acetyl-CoA + Malonyl-CoA = Acetoacetyl-CoA 2. Acetoacetyl-CoA + Malonyl-CoA = Palmitoyl-ACP 3. Palmitoyl-ACP = Palmitic Acid 4. Fatty acid elongation continues with each round of the cycle ### The Mevalonate Pathway - **Precursors:** Acetyl-CoA - **Products:** Isopentenyl pyrophosphate (IPP), terpenoids, steroids - **Steps:** 1. Acetyl-CoA + Acetoacetyl-CoA = β-Hydroxy-β-methylglutaryl-CoA 2. β-Hydroxy-β-methylglutaryl-CoA = Mevalonic acid 3. Mevalonic acid = Isopentenyl pyrophosphate (IPP) 4. IPP can be used to synthesize various terpenoids via the isoprene unit 5. Terpenoids are classified by the number of isoprene units: - Hemiterpenoids: C5 - Monoterpenoids: C10 - Sesquiterpenoids: C15 - Diterpenoids: C20 - Triterpenoids: C30 - Tetraterpenoids: C40 ### The Cholesterol Pathway - **Precursors:** Acetyl-CoA - **Products:** Cholesterol, steroid hormones (e.g., testosterone, estradiol), vitamin D, and bile acids - **Steps:** 1. Acetyl-CoA + Acetoacetyl-CoA = β-Hydroxy-β-methylglutaryl-CoA 2. β-Hydroxy-β-methylglutaryl-CoA = Mevalonic acid 3. Mevalonic acid = Isopentenyl pyrophosphate (IPP) 4. IPP is used to synthesize **farnesyl pyrophosphate** 5. Farnesyl pyrophosphate is used to synthesize **squalene** 6. Squalene undergoes a series of enzymatic steps to form **lanosterol** 7. Lanosterol is then converted to cholesterol and can be further processed to form other steroid compounds
