Small viruses

Small viruses, bacterial flagella, ribosomes, and even molecules can be seen by electron microscopy. However, to obtain a clear image in three dimensions requires a computer-based technique of image reconstruction or electron microscope tomography, which was developed initially by Aaron Klug and associates.344-349 A sample is mounted on a goniometer, a device that allows an object to be tilted at exact angles. Electron... 

Coxsackievirus is a small virus that can infect mammals. The genome of this virus consists of RNA (not DNA), and it contains only 7400 ribonucleotides. The... 

The use of an appropriate virus inoculum in the CPE reduction assay is extremely important, because either a large or a small virus inoculum may give misleading results in the drug-susceptibility profile. 

Bio-Gel P is a beaded polyacrylamide gel, and has separation properties similar to Sephadex . Bio-Gel A is a beaded agarose gel, like Sepharose it has the largest pore sizes known, and is even capable of separating small virus particles. 

Detailed understanding of the eukaryotic proteins that participate in DNA replication has come largely from studies with small viral DNAs, particularly SV40 DNA, the circular genome of a small virus that Infects monkeys. Figure 4-34 depicts the multiple proteins that coordinate copying of SV40 DNA at a replication fork. The assembled proteins at a replication fork further illustrate the concept of molecular machines introduced in Chapter 3. These multicomponent... 

Even a relatively small DNA chain can carry a large amount of information. For example, the DNA of a small virus, 5,000 nucleotides long, can have 4 ° possible sequences. This is a huge number—approximately 1 with 3,010 zeroes after it. (By comparison, the number of elementary particles in the universe is estimated at 10 °, or 1 with 80 zeroes after it.) But the virus has only one DNA sequence, which means that only one of the huge number of possible sequences has been selected to encode the virus s biochemical functions. In other words, there is information in the DNA sequence. The vims carries a large amount of information in a small space. 

Crick and Watson were the first to suggest that small viruses were built up of small protein subunits packed together symmetrically to form a protective shell for the nucleic acid. They reasoned that formation of small identical molecules was an efficient use of the limited information contained in the virus nucleic acid. They also realized that, of the types of symmetry possible for a three-dimensional structure enclosing space, only the cubic point groups could lead to an isometric particle, which was the known symmetry of many viruses at the time. Three types of cubic symmetry exist namely,... 

Interest in dendrimers is predicated in large part on the belief that size, shape, and composition matter. Dendrimers are synthetic polymers that— theoretically—are perfectly branched from a common core, giving rise to descriptions of two-dimensional representations that include tree-like or snowflake-like . As the products of synthesis, the size and composition of a dendrimer can be manipulated by choice of the starting materials. Commonly, triazines can reach protein-sized dimensions with an onset of globular structure. Larger triazine dendrimers that can reach the dimensions of small viruses have been reported. The literature is replete with examples of small dendrimers that can be viewed as floppy, randomly coiled oligomers. 

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