lecture _4 and 5 - Anatomy of a Virus Adenovirus (70-90 nm...

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Anatomy of a Virus In general, viruses consist of a nucleic acid genome (ssRNA, dsRNA, ssDNA, or dsDNA) housed inside a protein shell. In some cases, an outer membrane is also present. In 1962, Caspar et al. defined the following terms: The CAPSID denotes the protein shell that encloses the nucleic acid. It is built of structure units. STRUCTURE UNITS are the smallest functional equivalent building units of the capsid. CAPSOMERS are morphological units seen on the particle surfaces and represent clusters of structure units. The capsid together with its enclosed nucleic acid is called the NUCLEOCAPSID . The nucleocapsid may be surrounded by an ENVELOPE containing proteins from the host cell as well as several viral gene products. The VIRION is the complete infective virus particle Papillomavirus (55 nm in diameter) -A highly-regular geometric pattern can be recognized. Adenovirus (70-90 nm in diameter)
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Principles of Subunit Construction First Observation of Self-Assembly: In key experiments by Fraenkel Conrat and Williams (1955), it was shown that the tobacco mosaic virus spontaneously formed when mixtures of purified coat protein and its genomic RNA were incubated together. This means that the structure of TMV is self-ordered and therefore corresponds to a free energy minimum. Why do viral capsids assemble from multiple subunits? 1. Necessity: A triplet codon has a MW of 1000 and codes for an amino acid of average MW 150. Therefore, a nucleic acid can only code for 15% of its weight as a protein. As viruses are composed of 50-90% protein by weight, the only way to do this is to assemble a shell from redundant protein
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This note was uploaded on 02/16/2010 for the course MCB C 58381 taught by Professor Professorbrittglaunsinger,professorandyjackson during the Spring '10 term at University of California, Berkeley.

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lecture _4 and 5 - Anatomy of a Virus Adenovirus (70-90 nm...

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