Freeze fracture technique

Hostname: page-component-594f858ff7-c4bbg Total loading time: 0 Render date: 2023-06-14T02:28:22.268Z Has data issue: false Feature Flags: hasContentIssue false The freeze-fracture technique has been developed to study solid-liquid dispersions. In this technique, a sample of dispersion is frozen, then fractured. A replica of the fracture surface is made and observed using a scanning electron microscope. The physical form of the solid thickener in dispersion can be studied, and the structure of the thickener can be revealed as well as a combination of rupture properties of the solid and the frozen liquid. The application of this technique is on lubricant greases. Greases are two-phase dispersed systems composed of mineral oil gelled with solid particles of soap. Three lithium 12-hydroxystearate greases are examined. Two different kinds of washing of the replica are used, the first eliminating the liquid phase. The configuration of soap particles and the network formed by them are observed, and artifacts such as twisting soap fibers are avoided. The second washing eliminates the solid and liquid phase. Examination of the fracture surface of the soap provides information on crystalline arrangement. The observed structures by freeze fracture are related to the thermal treatments during grease manufacture. The results are compared with the observations obtained from an electron transmission microscope analysis after preparation by the usual dispersion technique. Martín-Alfonso...

Freeze fracture depends on the property of frozen tissues or cells, when cracked open, to split along the hydrophobic interior of membranes, thus revealing broad panoramas of membrane interior. These large panoramas reveal the three-dimensional contours of membranes making the methods well suited to studying changes in membrane architecture. Freshly split membrane faces are visualized by platinum or tungsten shadowing and carbon backing to form a replica that is then cleaned of tissue and imaged by TEM. Etching, i.e., removal of ice from the frozen fractured specimen by sublimation prior to shadowing, can also reveal the true surfaces of the membrane as well as the extracellular matrix and cytoskeletal networks that contact the membranes. Since the resolution of detail in the metal replicas formed is 1–2 nm, these methods can also be used to visualize macromolecules or macromolecular assemblies either in situ or displayed on a mica surface. These methods are available for either specimens that have been chemically fixed or specimens that have been rapidly frozen without chemical intervention. Freeze fracture units. ( a) The Balzers BAF 400. This model was available either with an oil diffusion pump (400D) or a turbomolecular pump (400T). ( b) The Leica BAF 060 which is equipped with a turbomolecular pump. ( c) The JEOL JFD II. This unit formerly used a turbomolecular pump but is now available from RMC/Boeckeler fitted with a cryopump. ( b) is a courtesy of Leica Microsyste...

Cytochemistry is the branch of cell biology dealing with the detection of cell constituents by means of biochemical analysis and visualization techniques. This is the study of the localization of cellular components through the use of staining methods. Cytochemistry is a science of localizing chemical components of cells and cell organelles on thin histological sections by using several techniques like enzyme localization, Freeze Fracture Enzyme Cytochemistry [ ] Freeze fracture enzyme cytochemistry was initially mentioned in the study of Pinto de silva in 1987. Origin [ ] Jean Brachet's research in Brussel demonstrated the localization and relative abundance between RNA and DNA in the cells of both animals and plants opened up the door into the research of cytochemistry. The work by Moller and Holter in 1976 about endocytosis which discussed the relationship between a cell's structure and function had established the needs of cytochemical research. Aims [ ] Cytochemical research aims to study individual cells that may contain several cell types within a tissue. It takes a nondestructive approach to study the localization of the cell. By remaining the cell components intact, researcher are able to study the intact cell activity rather than studying an isolated biochemical activity which the result may be influenced by the distorted cell membrane and spatial difference. References [ ] • Matoušková, Martina; Bílý, Tomáš; Bruňanská, Magdaléna; Mackiewicz, John S.; Nebesářová,...

Coating of samples is required in the field of electron microscopy to enable or improve the imaging of samples. Creating a conductive layer of metal on the sample inhibits charging, reduces thermal damage and improves the secondary electron signal required for topographic examination in the SEM. Fine carbon layers, being transparent to the electron beam but conductive, are needed for x-ray microanalysis, to support films on grids and back up replicas to be imaged in the TEM. The coating technique used depends on the resolution and application. The formvar covered TEM grids need to be coated with carbon to be conductive. Grids are treated with glow discharge otherwise solutions would not stick and distribute onto the grid. Freeze fractured samples are coated in a low angle with metal followed by a carbon backing up film (LeicaEMACE600 freeze fracture and LeicaEMVCT500 or LeicaEM ACE900) to produce a replica which can be imaged in a TEM. Sputter coating for SEM is the process of applying an ultra-thin coating of electrically-conducting metal – such as gold (Au), gold/palladium (Au/Pd), platinum (Pt), silver (Ag), chromium (Cr) or iridium (Ir) onto a non-conducting or poorly conducting specimen. Sputter coating prevents charging of the specimen, which would otherwise occur because of the accumulation of static electric fields. It also increases the amount of secondary electrons that can be detected from the surface of the specimen in the SEM and therefore increases the signal...

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Contents • 1 The Fluid Mosaic Model • 2 Proving the Fluid Mosaic Model • 2.1 Freeze Fracture & Electron Micrographs • 3 Lateral Diffusion • 4 Transverse Diffusion • 5 Control of Fluidity • 6 Melting Temperature • 7 Other Experiments • 8 References The Fluid Mosaic Model [ | ] The fluid mosaic model was originally proposed by S. Jonathan Singer and Garth Nicolson in 1972. Their idea of this model was to show and describe the general structure of a biological membrane. Biological membrane is composed of a lipid bilayer" that is essentially a two-dimensional solution composed of lipids and proteins. The lipid bilayer functions as both a solvent for integral proteins as well as a permeability barrier. To break down each part of the name of the model: The fluidity of the model is based on the hydrophobic components like proteins and lipids. These two components allow for the membrane to have a fluid motion since it is not solid; it is not made of only one type of macromolecule. The mosaic part of the name of the model is based on the fact that mosaics are created by using different pieces to obtain an overall picture. The mosaic model consists of not just one type of integral component but rather multiple (such as glycoproteins or phospholipids). Because of the model being made of different pieces, it creates a mosaic, hence the name. Proving the Fluid Mosaic Model [ | ] Freeze Fracture & Electron Micrographs [ | ] One aspect of the Fluid Mosaic Model is that membrane proteins ...