Chromosome micrograph

FIGURE 11.22 If the cell walls of bacteria such as Escherichia coli are partially digested and the cells are then osmotlcally shocked by dilution with water, the contents of the cells are extruded to the exterior. In electron micrographs, the most obvious extruded component is the bacterial chromosome, shown here surrounding the cell. (Dr. Gopal Murti/CNRI/Phototakr NYC)... 

FIG. 3. Chromosome arms begin to separate in pro metaphase. Scanning electron micrographs of human chromosomes isolated from cells in prophase (A), prometaphase (B), metaphase (C) and early anaphase (insert in C). Size bar, 1 /tm. Reprinted with permission from Sumner (1991). 

FIGURE 25-3 Visualization of bidirectional DNA replication. Replication of a circular chromosome produces a structure resembling the Greek letter theta (0). (a) Labeling with tritium (3H) shows that both strands are replicated at the same time (new strands shown in red). The electron micrographs illustrate the replication of a circular E. coli plasmid as visualized by autoradiography, (b) Addition of 3H for a... 

Laser scanning confocal micrograph of chromosomes at metaphase. Courtesy of Tom Moninger... 

DNA has been substituted in one strand.98 Since distances can be measured accurately on the electron micrographs, rather precise ( 50-100 bp) physical maps can be obtained. The chromosome map of phage K was mapped in this way initially now its complete nucleotide sequence is known. Another electron microscopic method is useful for location of AT-rich regions that denature readily. In a suitable concentration of formamide these regions melt to form visible single-stranded denaturation loops similar to the bubbles in Figure 26-6. 

Light micrograph of late mitosis in a plant. Microtubules are stained red and chromosomes are counterstained blue. (Courtesy of Andrew Bajer.)... 

I I Electron micrographs of the E. coli chromosome sug-jj gcst a folded circular structure containing about 40-f 100 supercoiled loops (diagrammatically indicated in fig. 25.16). It is believed that the folded structure is held together by an RNA-protein core, although the manner in which this is done is not well understood. The structure is further stabilized because the core forms a complex with positively charged polyamines and certain basic proteins. D. E. Pettijohn and his co-workers have provided evidence of such a core. They first showed that the individual super-... 

Fig. 2 Left cytoplasmic microtubules in interphase kidney epithelial cells imaged with the fluorescent paclitaxel derivative Flutax-2 (green) and nuclear DNA stained with Hoescht 33342 (blue). Right mitotic spindle from a dividing metaphase cell with similarly imaged microtubules and chromosomes. Bars indicate 10 pm (micrographs courtesy of Isabel Barasoain)...

Fig. 10 Micrograph of the ciliate Paramecium. Macronuclei of ciliates are more or less fragmented genomes (bags of chromosomes or genes) (Source of the image http //www.bio.umass.edu/biology/conn.river/parameci.html)...

A replicating bacterial chromosome exists as a so-called 9 structure (because of its appearance in electron micrographs and diagrammatically), in which the upper closed section represents the duplicated portion, or replication bubble. Why is there now an origin of replication situated at the middle of each arm of the bubble ... 

Figure 34.1 Motion within cells. This high-voltage electron micrograph shows the mitotic apparatus in a metaphase mammalian cell. The targe cylindrical objects are chromosomes, and the threadlike structures stretched across the center are microtubules—tracks for the molecular motors that move chromosomes. Many processes, including chromosome segregation in mitosis, depend on the action of molecular-motor proteins.. [Courtesy of Dr. J. R. McIntosh.]...

A EXPERIMENTAL FIGURE 10-23 An electron micrograph of a histone-depleted metaphase chromosome reveals the scaffold around which the DNA is organized. The long loops of DNA are visible extending from the nonhistone protein scaffold (the dark structure). The scaffold shape reflects that of the metaphase chromosome itself The chromosome was prepared from HeLa cells by treatment with a mild detergent. [From J. R. Paulson and U. K. Laemmli, 1977, Ce//12 817. Copyright 1977 MIT]... 

Harauz, G., Borland, L., Bahr, G. F., Zeitler, E., and van Heel, M. (1987). Three-dimensional reconstruction of a human metaphase chromosome from electron micrographs. Chromosoma 95,. 366-374. 

Fig. 2 Electron micrograph of a microspread mouse spermatocyte, stained with phosphotungstic acid. The axis of the X and Y chromosomes show a short synaptic region in the lower part of the figure. A nucleolar body (asterisk) is close to the XY pair. The autosomal bivalent (up) shows a recombination nodule (arrowhead). xSOOO.

Fig. 2 Electron micrograph of a typical transcription unit on a lampbrush chromosome loop from a stage VI Xenopus oocyte nucleus. These arc seen less frequently than endogenous ribosomal genes and injected plasmid genes. It is not possible to identify these genes beyond the fact that they are Pol II genes, but t hey lend to be very long and to have a reasonably high density of nascent transcripts. Scale bar, 1 pm.

In chromosomes, certain micrographs (figs. 6 and 7) suggest the existence of coiled bundles of DNA filaments. The whole system is a twisted network of helicoidal bundles of helical polymers. These bundles are likely to be microcrystals of DNA filaments, either due to preparation of the material for electron microscopy, or to the simple fact that DNA is very concentrated in chromosomes. Indeed, the presence of proteins (17) and ribonucleic acids (12,31,32) facilitate the condensation of DNA. In such microcrystalline bundles, there are two possible arrangements the hexagonal parallel packing or the dense twisted... 

Fig. 2. Electron micrograph of a rat kidney tubule cell in metaphase. The two kinetochores ( ki", "k2 ) of one chromosome are shown, as are chronriosomal microtubules C ch") and one pole ("p ), marked by a pair of centrioles. Approximately X40,000. ( From Jokelainen. 1967. J. Ultrastruct. Res., 19 19 4.)...

Fig. 3. Electron micrograph of metaphase in the micronucieus of the ciliate Blepharisma sp. showing both chromosomal microtubules (e.g., arrows at left) and interpolar microtubules (e.g., arrow at right). Note the fine fibrous material around the microtubules. X50,000. (From Jenkins. 1967. J. CeU. Biol., 34 463-481.)...

Fig. 16. Electron micrograph of a blood lily Haemanthus katherinae) chromosome in early mitotic prometaphase. Unipolar malorientation to a pole toward the left is suggested by the chromosomal microtubule arrangement at the two sister kinetochores ("ki/ The overall spindle axis is indicated by the arrow at the lower left side. The circle is a stain mark. XI 2,000. (From Bajer and Mole -Bajer. 1969. Chromosoma, 27 448-484.)...

Fig. 17. Electron micrograph of a Chinese hamster fibroblast in prophase. Portions of two chromosomes enclosed within the nuclear envelope are shown in one the two sister kinetochores I ki/ "k2") are visible note their "back-to-back" arrangement. X60,000. The material was not treated with colcemid Icf. Brinkley and Stubblefield, 1966) glutaraldehyde fixation, post-fixed in 0s04, uranyl and lead staining. (Unpublished micrograph courtesy of B. R. Brinkley.)...

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