Examples of crassulacean acid metabolism in the following topics:
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- Xerophytes, such as cacti and most succulents, also use
phosphoenolpyruvate (PEP) carboxylase to capture carbon dioxide in a process called crassulacean acid metabolism (CAM).
- In contrast to C4 metabolism, which physically separates the CO2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes.
- CAM plants store the CO2 mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate.
- Plants that do not use PEP-carboxylase in carbon fixation are called C3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle.
- Cross section of a CAM (crassulacean acid metabolism) plant, specifically of an agave leaf.
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- Metabolic pathways should be thought of as porous; that is, substances enter from other pathways and intermediates leave for other pathways.
- However, if there are excess amino acids, or if the body is in a state of starvation, some amino acids will be shunted into the pathways of glucose catabolism.
- The remaining atoms of the amino acid result in a keto acid: a carbon chain with one ketone and one carboxylic acid group.
- The keto acid can then enter the citric acid cycle.
- When deaminated, amino acids can enter the pathways of glucose metabolism as pyruvate, acetyl CoA, or several components of the citric acid cycle.
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- Like sugars and amino acids, the catabolic pathways of lipids are also connected to the glucose catabolism pathways.
- Thus, synthesis of cholesterol requires an intermediate of glucose metabolism.
- Triglycerides, a form of long-term energy storage in animals, are made of glycerol and three fatty acids.
- Animals can make most of the fatty acids they need.
- Fatty acids are catabolized in a process called beta-oxidation that takes place in the matrix of the mitochondria and converts their fatty acid chains into two carbon units of acetyl groups, while producing NADH and FADH2.
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- For example, one metabolic pathway for carbohydrates breaks large molecules down into glucose.
- Another metabolic pathway might build glucose into large carbohydrate molecules for storage.
- Consequently, metabolism is composed of these two opposite pathways:
- Other examples include the synthesis of large proteins from amino acid building blocks and the synthesis of new DNA strands from nucleic acid building blocks.
- Chemical reactions in metabolic pathways rarely take place spontaneously.
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- Peroxisomes neutralize harmful toxins and carry out lipid metabolism and oxidation reactions that break down fatty acids and amino acids.
- Peroxisomes perform important functions, including lipid metabolism and chemical detoxification.
- They also carry out oxidation reactions that break down fatty acids and amino acids.
- Reactive oxygen species (ROS), such as peroxides and free radicals, are the highly-reactive products of many normal cellular processes, including the mitochondrial reactions that produce ATP and oxygen metabolism.
- Peroxisomes are membrane-bound organelles that contain an abundance of enzymes for detoxifying harmful substances and lipid metabolism.
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- Uric acid is a compound similar to purines found in nucleic acids.
- The production of uric acid involves a complex metabolic pathway that is energetically costly in comparison to processing of other nitrogenous wastes such as urea (from the urea cycle) or ammonia; however, it has the advantages of reducing water loss and, hence, reducing the need for water.
- Uric acid is also less toxic than ammonia or urea.
- Uric acid is released in hypoxic conditions.
- Compare the major byproduct of ammonia metabolism in mammals to that of birds and reptiles
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- All organisms require energy to complete tasks; metabolism is the set of the chemical reactions that release energy for cellular processes.
- Animals consume food to replenish energy; their metabolism breaks down the carbohydrates, lipids, proteins, and nucleic acids to provide chemical energy for these processes.
- All of the chemical reactions that take place inside cells, including those that use energy and those that release energy, are the cell's metabolism.
- Muscle cells may consumer energy to build long muscle proteins from small amino acid molecules.
- Many cellular process require a steady supply of energy provided by the cell's metabolism.
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- This happens because all of the catabolic pathways for carbohydrates, proteins, and lipids eventually connect into glycolysis and the citric acid cycle pathways.
- Like sugars and amino acids, the catabolic pathways of lipids are also connected to the glucose catabolism pathways.
- Infants have an enzyme in the small intestine that metabolizes lactose to galactose and glucose.
- Fructose is absorbed from the small intestine and then passes to the liver to be metabolized, primarily to glycogen.
- Although the metabolism of fructose and glucose share many of the same intermediate structures, they have very different metabolic fates in human metabolism.
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- Essential nutrients are those that cannot be created by an animal's metabolism and need to be obtained from the diet.
- During digestion, digestible carbohydrates are ultimately broken down into glucose and used to provide energy through metabolic pathways.
- The omega-3 alpha-linolenic acid and the omega-6 linoleic acid are essential fatty acids needed to synthesize some membrane phospholipids.
- These amino acids are the "essential" amino acids.
- These include vitamins, omega 3 fatty acids, and some amino acids.
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- However, many organisms have developed strategies to carry out metabolism without oxygen, or can switch from aerobic to anaerobic cell respiration when oxygen is scarce.
- In these muscles, lactic acid accumulation must be removed by the blood circulation and the lactate brought to the liver for further metabolism.
- The chemical reactions of lactic acid fermentation are the following:
- Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.
- Pyruvic acid → CO2 + acetaldehyde + NADH → ethanol + NAD+