[工学]微生物学英文课件5.ppt

Chapter 5 Viruses The genomes of viruses can be composed of either DNA or RNA, and some use both as their genomic material at different stages in their life cycle. However , only one type of nucleic acid is found in the virion of any particular type of virus. C.Some animal viruses, such as adenovirus, have isometric symmetry and a DNA genome. 4. Replication of the virus nucleic acid. Formation of mRNA after infection of cells by viruses of different types. The chemical sense of the mRNA is considered as plus(+). The sense of the various virus nucleic acids are indicated as+if the same as mRNA, as–if opposite, or as+–if double–stranded. Examples are indicated next to the virus nucleic acid. The bacterial RNA viruses are all quite small, about 26 nm in size, and they are all icosahedral, with 180 copies of coat protein per virus particle. The complete nucleotide sequences of several RNA phage genomes are known. The genome of the RNA phage MS2, which infects Escherichia coli, is 3569 nucleotides long. The RNA strand in the virion acts directly as mRNA on entry into the cell. Such phages are called lysogenic phages or temperate phages. The participating bacterial host cells are known as lysogenic cells. (4) Expression of the viral genome so that viral nucleic acid and capsid components are synthesized, (5) Assembly of the viral particles within the host cell, and, (6) Release of the complete viral particles from the host plant cell. 5. Diameter of the virion or nucleocapsid 6. Number of capsomers in icosahedral viruses 7. Immunologic properties 8. Intracellular location of viral replication 3. Describe how a restriction endonuclease might play a role in resistance to bacteriophage infection. Why could a restriction endonuclease play such a role whereas a generalized DNase could not? 4. Typically, transfer RNA is used in translation. How-ever, it also plays a role in the replication of retroviralnucleic acid. Explain this role