The ionic strength dependence of chromatin folding

Under a variety of electron microscope specimen preparation techniques different forms of chromatin appearance can be distinguished: beads-on-a-string, a 100 Å nucleofilament, a 250 Å fiber and a compact 300 to 500 Å fiber.Using a standardized specimen preparation technique we wanted to find out whether there is any relation between these different forms of chromatin or not. We show that with increasing ionic strength a chromatin fiber consisting of a row of nucleo- somes progressively folds up into a solenoid-like structure with a diameter of about 300 Å.For the preparation of chromatin for electron microscopy the avoidance of stretching artifacts during adsorption to the carbon supports is of utmost importance. The samples are fixed with 0.1% glutaraldehyde at 4°C for at least 12 hrs. The material was usually examined between 24 and 48 hrs after the onset of fixation.

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II. Some new developments in specimen preparation techniques. Introductory remarks

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1971.0041 ◽

1971 ◽

Vol 261 (837) ◽

pp. 119-119 ◽

Cited By ~ 3

Keyword(s):

Electron Microscope ◽

Subject Matter ◽

Specimen Preparation ◽

Chemical Processing ◽

Preparation Technique ◽

Native State ◽

New Developments ◽

The Subject ◽

Restricted Use ◽

Preparation Techniques

The purpose of any specimen preparation technique is to prepare a sample of material ‘fixed’ in some way as near as possible to its native state, so that its structure has not changed significantly by the time the specimen is examined in the electron microscope, stained if necessary so that it gives adequate contrast, and, in some cases, additionally stained or labelled so that some chemically distinct part of the structure can be identified. Now, these techniques cover an enormous field of work, and at a relatively short meeting like this, one has to select some particular aspects of it. The subject-matter of section II is especially concerned with techniques which involve physical rather than chemical processing of the specimen, and in particular ones which are still only in rather restricted use.

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Specimen Preparation for Condoms

Microscopy Today ◽

10.1017/s155192950006123x ◽

2007 ◽

Vol 15 (5) ◽

pp. 40-41 ◽

Cited By ~ 1

Author(s):

Gan Phay Fang

Keyword(s):

Electron Microscope ◽

Scanning Electron Microscope ◽

Polymer Material ◽

Specimen Preparation ◽

Preparation Technique ◽

Sem Imaging ◽

Preparation Techniques ◽

Scanning Electron

Specimen preparation techniques for Scanning Electron Microscope (SEM) imaging of condoms as reported by Rosenzweig et al revealed a variety of artifacts. The artifacts were classified as ridging, cracking and melting. The purpose of this article is to introduce a simple specimen preparation technique for condoms to be evaluated via SEM without any surface artifacts. This technique involves the use of two chrome washers to sandwich the condom. The sandwiched condom specimen is then subjected to coating before mounting on an aluminium stub. The execution of this technique requires patience and practice so as not to damage the condom. The method may be applied to any similar polymer material.

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The Current Situation in Chemical Stabilization of Biological Materials

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100093912 ◽

1972 ◽

Vol 30 ◽

pp. 132-133

Author(s):

John H. Luft

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Osmium Tetroxide ◽

Molecular Level ◽

Cross Linking ◽

Chemical Stabilization ◽

Specimen Preparation ◽

Sufficient Condition ◽

Radio Telescopes

With information processing devices such as radio telescopes, microscopes or hi-fi systems, the quality of the output often is limited by distortion or noise introduced at the input stage of the device. This analogy can be extended usefully to specimen preparation for the electron microscope; fixation, which initiates the processing sequence, is the single most important step and, unfortunately, is the least well understood. Although there is an abundance of fixation mixtures recommended in the light microscopy literature, osmium tetroxide and glutaraldehyde are favored for electron microscopy. These fixatives react vigorously with proteins at the molecular level. There is clear evidence for the cross-linking of proteins both by osmium tetroxide and glutaraldehyde and cross-linking may be a necessary if not sufficient condition to define fixatives as a class.

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Electron Microscopy of Bacteriophage T7 Internal Head Proteins

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100116814 ◽

1975 ◽

Vol 33 ◽

pp. 638-639

Author(s):

P. Serwer

Keyword(s):

Electron Microscopy ◽

Bacteriophage T7 ◽

Specimen Preparation ◽

Dna Molecule ◽

The Core ◽

Internal Core ◽

Phage T7 ◽

T7 Phage ◽

Preparation Techniques ◽

Internal Head

The genome of bacteriophage T7 is a duplex DNA molecule packaged in a space whose volume has been measured to be 2.2 x the volume of the B form of T7 DNA. To help determine the mechanism for packaging this DNA, the configuration of proteins inside the phage head has been investigated by electron microscopy. A core which is roughly cylindrical in outline has been observed inside the head of phage T7 using three different specimen preparation techniques.When T7 phage are treated with glutaraldehyde, DNA is ejected from the head often revealing an internal core (dark arrows in Fig. 1). When both the core and tail are present in a particle, the core appears to be coaxial with the tail. Core-tail complexes sometimes dislodge from their normal location and appear attached to the outside of a phage head (light arrow in Fig. 1).

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Comparison of freeze-fractured yeast replicas using conventional TEM and low-voltage field-emission SEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100152343 ◽

1989 ◽

Vol 47 ◽

pp. 74-75

Author(s):

William P. Wergin ◽

Eric F. Erbe ◽

Terrence W. Reilly

Keyword(s):

Electron Microscope ◽

Scanning Electron Microscope ◽

Field Emission ◽

Low Voltage ◽

Objective Lens ◽

Specimen Preparation ◽

Lens System ◽

Air Drying ◽

Preparation Techniques ◽

Scanning Electron

Although the first commercial scanning electron microscope (SEM) was introduced in 1965, the limited resolution and the lack of preparation techniques initially confined biological observations to relatively low magnification images showing anatomical surface features of samples that withstood the artifacts associated with air drying. As the design of instrumentation improved and the techniques for specimen preparation developed, the SEM allowed biologists to gain additional insights not only on the external features of samples but on the internal structure of tissues as well. By 1985, the resolution of the conventional SEM had reached 3 - 5 nm; however most biological samples still required a conductive coating of 20 - 30 nm that prevented investigators from approaching the level of information that was available with various TEM techniques. Recently, a new SEM design combined a condenser-objective lens system with a field emission electron source.

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Transmission Electron Microscopy (TEM) Specimen Preparation Technique using Focused Ion Beam (FIB): Application to Material Characterization of Chemical Vapor Deposition of Tungsten (W) and Tungsten Silicides (WSix)

ISTFA 1997: Conference Proceedings from the 23rd International Symposium for Testing and Failure Analysis ◽

10.31399/asm.cp.istfa1997p0237 ◽

1997 ◽

Author(s):

K. Doong ◽

J.-M. Fu ◽

Y.-C. Huang

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Chemical Vapor Deposition ◽

Vapor Deposition ◽

Focused Ion Beam ◽

Ion Beam ◽

Chemical Vapor ◽

Specimen Preparation ◽

Preparation Technique ◽

Transmission Electron

Abstract The specimen preparation technique using focused ion beam (FIB) to generate cross-sectional transmission electron microscopy (XTEM) samples of chemical vapor deposition (CVD) of Tungsten-plug (W-plug) and Tungsten Silicides (WSix) was studied. Using the combination method including two axes tilting[l], gas enhanced focused ion beam milling[2] and sacrificial metal coating on both sides of electron transmission membrane[3], it was possible to prepare a sample with minimal thickness (less than 1000 A) to get high spatial resolution in TEM observation. Based on this novel thinning technique, some applications such as XTEM observation of W-plug with different aspect ratio (I - 6), and the grain structure of CVD W-plug and CVD WSix were done. Also the problems and artifacts of XTEM sample preparation of high Z-factor material such as CVD W-plug and CVD WSix were given and the ways to avoid or minimize them were suggested.

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Meso tetrakis ortho-, meta-, and para-N-alkylpyridiniopor-phyrins: kinetics of copper(II) and zinc(II) incorporation and zinc porphyrin demetalation

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424603000197 ◽

2003 ◽

Vol 07 (03) ◽

pp. 139-146 ◽

Cited By ~ 6

Author(s):

Peter Hambright ◽

Ines Batinić-Haberle ◽

Ivan Spasojević

Keyword(s):

Aqueous Solution ◽

Ionic Strength ◽

Effective Charge ◽

Methyl Ethyl ◽

Ionic Strength Dependence ◽

Zinc Porphyrin ◽

Cationic Porphyrin ◽

Strength Dependence ◽

Acid Catalyzed ◽

Kinetics Of

The relative reactivities of the tetrakis( N -alkylpyridinium- X - yl )-porphyrins where X = 4 (alkyl = methyl, ethyl, n -propyl) , X = 3 (methyl) , and X = 2 (methyl, ethyl, n -propyl, n -butyl, n -hexyl, n -octyl) were studied in aqueous solution. From the ionic strength dependence of the metalation rate constants, the effective charge of a particular cationic porphyrin was usually larger when copper(II) rather than zinc(II) was the reactant. The kinetics of ZnOH + incorporation and the acid catalyzed removal of zinc from the porphyrins in 1.0 M HCl were also studied. In general, the more basic 4- (para-) and 3- (meta-) isomers were the most reactive, followed by the less basic 2- (ortho-) methyl to n -butyl derivatives, with the lipophilic ortho n -hexyl and n -octyl porphyrins the least reactive.

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