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October, 2006
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Proton Pumps: Integral membrane proteins that transport protons across a membrane. This transport can be linked to the hydrolysis of Adenosine triphosphate. What is referred to as proton pump inhibitors frequently is about Potassium hydrogen atpase.

The Apoplast and Symplast

JoVE 11106

Plant growth depends on its ability to take up water and dissolved minerals from the soil. The root system of every plant is equipped with the necessary tissues to facilitate the entry of water and solutes. The plant tissues involved in the transport of water and minerals have two major compartments - the apoplast and the symplast. The apoplast includes everything outside the plasma membrane of living cells and consists of cell walls, extracellular spaces, xylem, phloem, and tracheids. The symplast, in contrast, consists of the entire cytosol of all living plant cells and the plasmodesmata - which are the cytoplasmic channels interconnecting the cells. There are several potential pathways for molecules to move through the plant tissues: The apoplastic, symplastic, or transmembrane pathways. The apoplastic pathway involves the movement of water and dissolved minerals along cell walls and extracellular spaces. In the symplastic route, water and solutes move along the cytosol. Once in this pathway, materials need to cross the plasma membrane when moving from cell to neighboring cell, and they do this via the plasmodesmata. Alternatively, in the transmembrane route, the dissolved minerals and water move from cell to cell by crossing the cell wall to exit one cell and enter the next. These three pathways are not mutually exclusive, and some solutes may use more than on

 Core: Biology

ATP Yield

JoVE 11008

Cellular respiration produces 30-32 ATP molecules per glucose molecule. Although most of the ATP results from oxidative phosphorylation and the electron transport chain (ETC), 4 ATP are gained beforehand (2 from glycolysis and 2 from the citric acid cycle).

The ETC is embedded in the inner mitochondrial membrane and comprises four main protein complexes and an ATP synthase. NADH and FADH2 pass electrons to these complexes, which in turn pump protons into the intermembrane space. This distribution of protons generates a concentration gradient across the membrane. The gradient drives the production of ATP when protons flow back into the mitochondrial matrix via the ATP synthase. For every 2 input electrons that NADH passes into complex I, complexes I and III each pump 4 protons and complex IV pumps 2 protons, totaling 10 protons. Complex II is not involved in the electron chain initiated by NADH. FADH2, however, passes 2 electrons to complex II, so a total of 6 protons are pumped per FADH2; 4 protons via complex III and 2 via complex IV. Four protons are needed to synthesize 1 ATP. Since 10 protons are pumped for every NADH, 1 NADH yields 2.5 (10/4) ATP. Six protons are pumped for every FADH2, so 1 FADH2 yields 1.5 (6/4) ATP. Cellular respiration produces a maximum of 10 NADH and 2 FADH2

 Core: Biology

Short-distance Transport of Resources

JoVE 11097

Short-distance transport refers to transport that occurs over a distance of just 2-3 cells, crossing the plasma membrane in the process. Small uncharged molecules, such as oxygen, carbon dioxide, and water, can diffuse across the plasma membrane on their own. In contrast, ions and larger molecules require the assistance of transport proteins due to their charge or size. Transport across membranes also occurs within individual cells, playing a variety of essential roles for the plant as a whole. Resources are transported into and out of the central vacuole within each plant cell One of the roles of the large central vacuole of a plant cell is the storage of resources. Active and passive transport proteins are found in the vacuolar membrane, or tonoplast, just as they are found in the plasma membrane of the cell, and they regulate the movement of solutes between the cytoplasm and vacuole. Sugar can be stored for later, ions are sequestered from the cytoplasm, and protons, in particular, are pumped into the vacuole, creating an acidic environment for breaking down unwanted or toxic substances that enter the cell. Movement across the tonoplast controls turgor pressure In addition to its role in storage, the vacuole generates turgor pressure - a force that pushes the plasma membrane against the cell wall -

 Core: Biology

Cryogenic Liquid Jets for High Repetition Rate Discovery Science

1SLAC National Accelerator Laboratory, 2University of Alberta, 3Friedrich-Alexander-Universität Erlangen-Nürnberg, 4European XFEL, 5Helmholtz-Zentrum Dresden-Rossendorf, 6Technische Universität Dresden, 7Technische Universität Darmstadt

JoVE 61130

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