mitochondria

Examples of mitochondria in the following topics:

• Mitochondria

  • One of the major features distinguishing prokaryotes from eukaryotes is the presence of mitochondria.
  • Mitochondria are double-membraned organelles that contain their own ribosomes and DNA.
  • These features all support the hypothesis that mitochondria were once free-living prokaryotes.
  • In mitochondria, this process uses oxygen and produces carbon dioxide as a waste product.
  • In addition to the aerobic generation of ATP, mitochondria have several other metabolic functions.

• The Evolution of Mitochondria

  • One of the major features distinguishing prokaryotes from eukaryotes is the presence of mitochondria.
  • Mitochondria arise from the division of existing mitochondria.
  • However, mitochondria cannot survive outside the cell.
  • These features all support that mitochondria were once free-living prokaryotes.
  • Despite the transfer of genes between mitochondria and the nucleus, mitochondria retain much of their own independent genetic material.

• Endosymbiotic Theory and the Evolution of Eukaryotes

  • This mechanism is an aspect of the Endosymbiont Theory, which is accepted by a majority of biologists as the mechanism whereby eukaryotic cells obtained their mitochondria and chloroplasts.
  • This mechanism has also been used to explain the double membranes found in mitochondria and chloroplasts.
  • Another hypothesis, the nucleus-first hypothesis, proposes the nucleus evolved in prokaryotes first, followed by a later fusion of the new eukaryote with bacteria that became mitochondria.
  • The mitochondria-first hypothesis, however, proposes mitochondria were first established in a prokaryotic host, which subsequently acquired a nucleus (by fusion or other mechanisms) to become the first eukaryotic cell.
  • The theory that mitochondria and chloroplasts are endosymbiotic in origin is now widely accepted.

• ATP Yield

  • Another source of variance occurs during the shuttle of electrons across the membranes of the mitochondria.
  • The NADH generated from glycolysis cannot easily enter mitochondria.
  • Thus, electrons are picked up on the inside of mitochondria by either NAD+ or FAD+.

• Endosymbiosis and the Evolution of Eukaryotes

  • Ivan Wallin extended the idea of an endosymbiotic origin to mitochondria in the 1920s.
  • More detailed electron microscopic comparisons between cyanobacteria and chloroplasts combined with the discovery that plastids (organelles associated with photosynthesis) and mitochondria contain their own DNA led to a resurrection of the idea in the 1960s.
  • A eukaryote with mitochondria engulfed a cyanobacterium in an event of serial primary endosymbiosis, creating a lineage of cells with both organelles.

• The Evolution of Plastids

  • Like mitochondria, plastids appear to have a primary endosymbiotic origin, but differ in that they derive from cyanobacteria rather than alpha-proteobacteria.
  • There is also, as with the case of mitochondria, strong evidence that many of the genes of the endosymbiont transferred to the nucleus.
  • Plastids, like mitochondria, cannot live independently outside the host.
  • In addition, like mitochondria, plastids derive from the binary fission of other plastids.

• Excavata

  • Until recently, these protists were believed to lack mitochondria.
  • A second Excavata subgroup, the parabasalids, also exhibits semi-functional mitochondria.

• Connecting Lipids to Glucose Metabolism

  • 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.

• Characteristics of Eukaryotic Cells

  • numerous membrane-bound organelles (including the endoplasmic reticulum, Golgi apparatus, chloroplasts, and mitochondria)
  • Mitochondria are oval-shaped, double membrane organelles that have their own ribosomes and DNA.
  • Mitochondria are also important in cellular respiration.

• Comparing Plant and Animal Cells

  • Each eukaryotic cell has a plasma membrane, cytoplasm, a nucleus, ribosomes, mitochondria, peroxisomes, and in some, vacuoles; however, there are some striking differences between animal and plant cells.
  • Like mitochondria, chloroplasts have their own DNA and ribosomes, but chloroplasts have an entirely different function.
  • Like mitochondria, chloroplasts have outer and inner membranes, but within the space enclosed by a chloroplast's inner membrane is a set of interconnected and stacked fluid-filled membrane sacs called thylakoids .