biogeochemical cycle

Examples of biogeochemical cycle in the following topics:

• Biogeochemical Cycles

  • The elemental components of organic matter are cycled through the biosphere in an interconnected process called the biogeochemical cycle.
  • Because geology and chemistry have major roles in the study of this process, the recycling of inorganic matter between living organisms and their environment is called a biogeochemical cycle.
  • The components of organic molecules are constantly being stored and recycled as part of their biogeochemical cycle.
  • The cycling of all of these elements is interconnected.
  • Thus, mineral nutrients are cycled, either rapidly or slowly, through the entire biosphere, from one living organism to another, and between the biotic and abiotic world.

• The Carbon Cycle

  • Carbon enters the atmosphere in the form of carbon dioxide via the carbon cycle and returns to organic carbon via photosynthesis.
  • The carbon cycle is most easily studied as two interconnected sub-cycles: one dealing with rapid carbon exchange among living organisms and the other dealing with the long-term cycling of carbon through geologic processes .
  • Gas exchange through the atmosphere and water is one way that the carbon cycle connects all living organisms on Earth.
  • This is another example of how human activity indirectly affects biogeochemical cycles in a significant way.
  • Volcanic activity and human emissions bring this stored carbon back into the carbon cycle.

• Introduction to Ecology

  • Ecosystem processes, such as primary production, pedogenesis (the formation of soil), nutrient cycling, and various niche construction activities, regulate the flux of energy and matter through an environment.
  • Ecosystems sustain life-supporting functions and produce natural capital, such as biomass production (food, fuel, fiber and medicine), the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, and many other natural features of scientific, historical, economic, or intrinsic value.

• The Carbon Cycle

• Acetyl CoA to CO2

  • The acetyl carbons of acetyl CoA are released as carbon dioxide in the citric acid cycle.
  • Acetyl CoA links glycolysis and pyruvate oxidation with the citric acid cycle.
  • In addition to the citric acid cycle, named for the first intermediate formed, citric acid, or citrate, when acetate joins to the oxaloacetate, the cycle is also known by two other names.
  • Additionally, the cycle is known as the Krebs cycle, named after Hans Krebs, who first identified the steps in the pathway in the 1930s in pigeon flight muscle.
  • Describe the fate of the acetyl CoA carbons in the citric acid cycle

• Regulator Molecules of the Cell Cycle

  • Cyclins regulate the cell cycle only when they are tightly bound to Cdks.
  • The second group of cell cycle regulatory molecules are negative regulators.
  • Negative regulators halt the cell cycle.
  • Rb halts the cell cycle by binding E2F.
  • The concentrations of cyclin proteins change throughout the cell cycle.

• The Lytic and Lysogenic Cycles of Bacteriophages

  • Bacteriophages, viruses that infect bacteria, may undergo a lytic or lysogenic cycle.
  • Bacteriophages may have a lytic cycle or a lysogenic cycle, and a few viruses are capable of carrying out both.
  • An example of a bacteriophage known to follow the lysogenic cycle and the lytic cycle is the phage lambda of E. coli.
  • A temperate bacteriophage has both lytic and lysogenic cycles.
  • In the lytic cycle, the phage replicates and lyses the host cell.

• Citric Acid Cycle

  • The last step in the citric acid cycle regenerates oxaloacetate by oxidizing malate.
  • Each turn of the cycle forms three NADH molecules and one FADH2 molecule.
  • One GTP or ATP is also made in each cycle.
  • Several of the intermediate compounds in the citric acid cycle can be used in synthesizing non-essential amino acids; therefore, the cycle is amphibolic (both catabolic and anabolic).
  • Because the final product of the citric acid cycle is also the first reactant, the cycle runs continuously in the presence of sufficient reactants.

• Regulation of the Cell Cycle at Internal Checkpoints

  • The cell cycle is controlled by three internal checkpoints that evaluate the condition of the genetic information.
  • A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be halted until conditions are favorable (e.g. the DNA is repaired).
  • Cyclins are cell-signaling molecules that regulate the cell cycle.
  • The cell cycle is controlled at three checkpoints.
  • Explain the effects of internal checkpoints on the regulation of the cell cycle

• Proto-oncogenes

  • The genes that code for the positive cell cycle regulators are called proto-oncogenes.
  • Consider what might happen to the cell cycle in a cell with a recently-acquired oncogene.
  • The result is detrimental to the cell and will likely prevent the cell from completing the cell cycle; however, the organism is not harmed because the mutation will not be carried forward.
  • In addition to the cell cycle regulatory proteins, any protein that influences the cycle can be altered in such a way as to override cell cycle checkpoints.
  • An oncogene is any gene that, when altered, leads to an increase in the rate of cell cycle progression.