(PDF) Complete Journal PLCHB4 39(1) 111-245 (2007) ISSN 0748-6642
(PDF) Complete Journal PLCHB4 39(1) 1-110 (2007) ISSN 0748-6642
Fermentation reactions occur in the cytoplasm of both prokaryotic and eukaryotic cells. In the absence of oxygen, pyruvate does not enter the mitochondria in eukaryotic cells.
PCP provides a forum for the review and publication of reports of original research in a broad range of subjects in biophysics, biochemistry and cellular physiology. Reports of direct applications of basic knowledge to human studies are invited; examples would include the measurements of relaxation times as part of NMR imaging. Single experiments, conclusions based on inadequate statistics, purely speculative
(PDF) Complete Journal PLCHB4 38(1) 1-76 (2006) ISSN 0748-6642
Some cells make ATP solely via substrate-level phosphorylation, either because they lack the electron transport chain, or because suitable terminal electrons acceptors are unavailable. They use glycolysis to make 2 ATP and 2 pyruvates from a molecule of glucose, plus 2 NADH. However, such cells cannot continue running glycolysis indefinitely because they quickly run out of NAD+, when all available NAD+ has been reduced to NADH. In respiring cells, NADH dumps electrons to the electron transport chain and regenerates NAD+. In the absence of respiration, this method of regenerating NAD+ is not available.
Fermentation reactions pyruvate with electrons from NADH to regenerate NAD+ (opposite of pyruvate oxidation). These reactions produce ethanol in yeast, and lactic acid in mammalian cells (muscle cells under oxygen deficit and most tumor cells – see Warburg effect below).
(PDF) Complete Journal PLCHB4 37(2) 89-161 (2006) ISSN 0748-6642
Ethanol fermentation regenerates NAD+ from NADH by releasing CO2 from pyuvate and reducing the two-carbon acetaldehyde molecule to ethanol. Image by Davidcarmack retrieved from Wikimedia commons.
The Nobel Prize winner Otto Warburg observed that many, and perhaps most, cancer cells derive most of their energy from glycolysis and lactic acid fermentation, even when oxygen is plentiful (see review by Liberti and Locasale, 2016). Several explanations have been proposed. One is that cancer cells can promote biosynthesis and cell growth by NOT respiring organic carbon to CO2, and using the organic carbon to build cellular biomolecules, instead. Another hypothesis is that ramping up glycolysis allows tumor cells to out-compete normal cells or immune system cells for glucose. A third hypothesis is that lactic acid secretion causes changes in the tumor cells’ environment that favors tumor cell growth and spread.
(PDF) Complete Journal PLCHB4 37(1) 1-88 (2005) ISSN 0748-6642
(PDF) Complete Journal PLCHB4 36(1) 85-160 (2004) ISSN 0748-6642
(PDF) Complete Journal PLCHB4 36(1) 1-88 (2004) ISSN 0748-6642
(PDF) Complete Journal PLCHB4 35(2) 91-171 (2003) ISSN 0748-6642
(PDF) Complete Journal PLCHB4 35(1) 1-90 (2003) ISSN 0748-6642
Volume 29, Number 2, 1997 PLCHB4 29(2) 123-262 (1979) ISSN 0748-6642
Volume 30 (1998)
Cancer and lactic acid fermentation – the Warburg effect
In prokaryotic cells, all the metabolic pathways occur in the cytoplasm, except for chemiosmosis and oxidative phosphorylation, which occur on the plasma membrane. Prokaryotic cells are capable of anaerobic respiration using alternative electron acceptors such as nitrate and sulfate, although they prefer oxygen as the terminal electron acceptor to drive chemiosmotic ATP synthesis. In the absence of any suitable electron acceptor, they use fermentation pathways.
Energy metabolism in eukaryotes vs prokaryotes
In eukaryotic cells, glycolysis and fermentation reactions occur in the cytoplasm. The remaining pathways, starting with pyruvate oxidation, occur in the mitochondria. Most eukaryotic mitochondria can use only oxygen as the terminal electron acceptor for respiration. In the presence of oxygen, pyruvate enters the mitochondrial matrix and is oxidized to acetyl-CoA, and then to CO2 via the citric acid cycle. The electron transport chain and ATP synthase are located on the mitochondrial inner membrane.
Endosymbiont theory for origin of mitochondria
Energy metabolism in eukaryotic cells, from Wikipedia. This is a highly condensed illustration. Students should identify the various compounds and talk through (explain) this diagram.
A couple of music videos for your study breaks:
The location of the electron transport chain on the inner mitochondrial membrane, and the pyruvate oxidation and citric acid cycle in the mitochondrial matrix, makes sense in light of the endosymbiont theory for the origin of mitochondria. These locations correspond to the plasma membrane and cytoplasm of the aerobic bacterial endosymbiont, most likely an alpha-proteobacterium, that was the ancestor of mitochondria. The outer mitochondrial membrane derived from the endosomal membrane that originally engulfed the endosymbiont.
Amazingly concise!! Bravo, Choi, bravo!
Further evidence to support the endosymbiont theory is that mitochondria have their own DNA, in the form of a circular chromosome that is topologically like bacterial chromosomes. The sequence of the mitochondrial DNA most closely resembles the sequences of genes in alpha-proteobacteria. Mitochondrial ribosomes are structurally more similar to bacterial ribosomes than to eukaryotic ribosomes. Mitochondria reproduce in eukaryotic cells by fission, again resembling bacterial cell division.
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