crassulacean acid metabolism

(noun)

A carbon fixation pathway that evolved in some plants as an adaptation to arid conditions, in which the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2).

Related Terms

  • C4 carbon fixation
  • Crassulacean acid metabolism (CAM).
  • C4 Carbon Fixation

Examples of crassulacean acid metabolism in the following topics:

  • CAM and C4 Photosynthesis

    • 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.
  • Connecting Proteins to Glucose Metabolism

    • 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.
  • Connecting Lipids to Glucose Metabolism

    • 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.
  • Metabolic Pathways

    • 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.
  • Peroxisomes

    • 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.
  • Nitrogenous Waste in Birds and Reptiles: Uric Acid

    • 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
  • The Role of Energy and Metabolism

    • 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.
  • Connecting Other Sugars to Glucose Metabolism

    • 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.
  • Food Requirements and Essential Nutrients

    • 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.
  • Anaerobic Cellular Respiration

    • 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+
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.