Tunelling

TUNEL is the name given to the in-situ DNA endlabelling technique which serves as a marker of apoptotic cells. This method is based on the specific binding of terminal de-oxy nucleotidyl transferases to the 3-hydroxy ends of DNA. The technique is normally used for examination under the light microscope but can also be adapted for examination under the electron microscope. 

Since the pioneering work of Rohrer and Binning,77 scanning tunelling microscopy (STM) has been used to image atomic-scale features of electrically conductive surfaces under ultra-high-vacuum but also at atmospheric pressure and in aqueous electrochemical environments. The ability of STM to image chemisorption and surface reconstruction is well... 

Figure 5.48. Schematic of the experimental setup for using Scanning Tunelling Microscopy (STM) to investigate a Pt(lll) catalyst-electrode surface.78 Reprinted with permission from Elsevier Science.

Figure 5.49. (a) STM image (unfiltered) of the initially sodium-contaminated Pt(l 1 l)-(2x2)-0 adlattice (b) corresponding Fourier transform spectrum (c) Fourier-filtered STM image of the overlapping Pt(l 1 l)-(2x2)-0 and Pt(111)-(12x12)-Na adlayers (bias Ut = 80 mV, tunelling current I, = 10 nA, total scan size 319 A).78 Reprinted with permission from Elsevier Science. 

The terminal dUTP nick end labeling assay (TUNEL reaction) and electrophoretic analysis of DNA/organotin(IV) mixtures allowed the investigation of DNA fragmentation. 

Malm G, Lying-Tunell U Cerebellar dysfunction related to toluene sniffing. Acta Neurol Scand 62 188-190, 1980... 

CLARKE R G, LUND E K, JOHNSON I T aud PINDER A c (2000) Apoptosis cau he detected in attached colonic adenocarcinoma HT29 cells using annexin V binding, hut uot hy TUNEL assay or suh-GO DNA content . Cytometry, 39 141-50. 

Basran J, RJ Harris, MJ Sutcliffe, NS Scrutton (2003) H-tuneling in the multiple H-transfers of the catalytic cycle of morphinone reductase and in the reductive half-reaction of the homologous pentaerythritol tetranitrate reductase. J Biol Chem 278 43973-43982. 

Such is the richness and intellectual vibrancy of the field of RI chemistry that an additional book was needed to cover silicon, germanium and tin centered RFs, as well as tetrahedral intermediates and topics of increasing importance such as quantum mechanical tunelling, conical intersections, solid-state chemistry, and combustion chemistry. These topics are covered in this new book. 

The most familiar argument that postulates quantum-mechanical tunelling to occur in an, otherwise classical, chemical system, is the common explanation of the ease whereby an ammonia molecule manages to invert itself. 

Apoptosis or programmed cell death is one of the regulatory mechanisms for the removal of unwanted cells. Apoptosis is induced by the stimulation of several different cell surface receptors in association with caspase activation. Apoptosis of a cell is thus a complicated process and can be assayed by various methods. Among widely used methods, the TUNEL assay is described here. 

TUNEL Assay (Terminal Transferase dUTP Nick End Labelling)... 

TUNEL terminal transferase dUTP nick end labelling... 

Fig. 1. Labeling of degraded chromatin by the TUNEL assay. During apoptosis endogenous, endonucleases cleave chromatin in the hnker region between nucleosomes. The resulting nucleosome multimers are labeled by TdT and a dUTP analog with a detectable label (biotin, DIG, or FITC) shown as. The additional nucleotide in the reaction (here shown as dCTP) may be any dNTP and serves to extend the labeling reaction by preventing steric hindrance by two adjacent labeled dUTPs. (Abbreviations are as in text.)...

Fig. 2. Apoptotic cells fluorescently labeled using the TUNEL assay. Fixed paraffin-embedded rat mammary glands, 4 d postweaning (obtained from Oncor), were labeled using the TUNEL assay to detect apoptotic cells. Reagents were from Oncor s Apoptag Direct In Situ Apoptosis Detection Kit (Fluorescein), which directly incorporates fluorescein-labeled dUTP in the TdT end-labeling reaction. All reagents were used as described by the manufacturer (see Note 1). (Abbreviations are as in text.)...

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