Archive for October 2011
Liquid Scintillation Signal Interpretation
A beta particle, passing through a scintillation cocktail, leaves a trail of energized solvent molecules. These excited solvent molecules transfer their energy to scintillator molecules, which give off light. Each scintillator molecule gives off only one photon on activation, (and the wavelength of that photon is characteristic of the scintillator, not the ß-particle), but multiple…
Read MoreRadioactive Emissions and the Use of Isotopes in Research
Radioactive decay occurs with the emission of particles or electromagnetic radiation from an atom due to a change within its nucleus. Forms of radioactive emission include alpha particles (α), beta particles (β), and gamma rays (γ). α particles are the least energetic, most massive of these decay products. An α particle contains two protons and…
Read MoreHydrogen Peroxide Detection: The Methods
In at least one important way, measuring hydrogen peroxide is substantially easier than measuring superoxide. Superoxide is unstable in aqueous solution—its steady state concentration cannot be measured directly. As a result, superoxide “levels” must be determined indirectly. This can be done by either (a) measuring rates of production and removal and then correlating the two,…
Read MoreHydrogen Peroxide Detection: An Overview
Hydrogen peroxide, like superoxide, can react with a variety of targets in the cell, and has been associated with a number of diseases. Aerobic organisms express catalase and peroxidase enzymes to prevent damage by H2O2. Peroxidases—most of which contain a heme at their active site—undergo an enzymatic cycle in which a molecule of peroxide oxidizes…
Read MoreSuperoxide Detection
Overview Superoxide has been implicated in diseases ranging from Alzheimer’s to diabetes. The wide range of pathologies associated with superoxide is the result of its ability to react with a variety of cellular targets, including enzyme active sites, nucleic acids and lipids. Cells protect themselves against superoxide damage by producing superoxide dismutase enzymes (SODs). These…
Read MoreReactive Oxygen Species
Oxygen is used by a great variety of organisms as a means for producing energy. The redox potential of the oxygen-water couple is 1.229 Volts, meaning that a relatively large amount of energy is released during the 4 electron reduction which converts O2 to H2O. The incorporation of this reaction into cellular metabolism was an enabling…
Read MoreStaining Tissue Sections for Electron Microscopy
Although secondary fixation in osmium tetroxide provides some areas of electron density, this is usually not sufficient to provide high contrast, high definition images. A number of staining techniques are available to enhance the contrast of areas of interest. These fall into two major categories. Positive stains deposit electron dense material on the area of…
Read MoreSectioning Tissue for Electron Microscopy
The ultrathin sections required in TEM are cut with knives of glass, diamond or sapphire. These materials produce extremely hard, ultrasharp edges, but they are brittle and subject to damage. Glass knives are produced as needed by fracturing. Sapphire knives and diamond knives may be purchased. The high cost of diamond knives possibly makes resharpening…
Read MoreTissue Processing for Electron Microscopy
Sections for TEM must be less than 80 nm thick in order to allow at least 50% of the electron beam to penetrate the sample. This can only be accomplished by using resins for embedding (epoxy, acrylic or polyester) which requires a modification of the processing protocol. Graded alcohol baths (typically 20, 40, 70, 90…
Read MoreFixing Tissue for Electron Microscopy
The most popular fixatives for TEM work are aldehydes and osmium tetroxide. Aldehyde based fixatives react with amines and other nucleophiles in the tissue, most notably lysine and arginine, generating cross-linked proteins. The cross linking action of these fixatives stabilizes the cytosol, preserving cellular structures. Aldehydes do not react with most lipids, so membrane components…
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