micro chapter 8 review questions

What are the basic components of a virus?

- Contains nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material (capsid/capsomere) (naked and enveloped viruses)

How is a lytic virus different from a latent virus? What other terms are used to describe latent viruses?

- In the lytic cycle the host cell is killed, in latent the host remains alive and phage DNA recombines with bacterial chromosome. In the latent cycle the phage also remains dormant, inactive. - Many lytic viruses cause cancer - lysogenic viruses

What is unique about retroviruses? Name a retrovirus. Describe how retroviruses reproduce.

- Retroviruses are RNA viruses that contain the enzyme reverse transcriptase. Reverse transcriptase copies the single stranded RNA into double stranded DNA which then integrates into the host chromosome and becomes a provirus. - HIV - Entrance into the cell Removal of virion envelope at the membrane Reverse transcription of one of the two RNA genomes Integration of retroviral DNA into host genome Transcription of retroviral DNA Assembly and packaging of genomic RNA Budding of enveloped virions; release from cell

How are T4 and Lambda similar and different?

- T4: lyse the host (breaking cell with the virus.) T4 is a LYTIC bacteriophage that infects its host, E. coli. To get into the host the phage has to poke a hole in the bacterial cell wall. To do this it uses lysozyme and then contracts to inject its DNA into the bacterial cytoplasm. - Lambda: LYSOGENIC/ latent/ temperate: meaning that the viral DNA incorporates into the host chromosome. Forms a prophage. - both are bacteriophages and doublestranded DNA

How is the penetration step in viral replication different in phages and animal viruses? What else would be different in their replication?

- The phages inject their nucleic acid into the bacteria and the capsid stays on the outside of the host. - Animal viruses are taken completely into the host cell and must be uncoated to release the viral nucleic acid. - One of the major differences between phages and animal viruses is that the capsid of phages is left outside the host following penetration and with the animal viruses the entire virus is taken into the host and must be uncoated to release the nucleic acid. Remember that animal cells are eukaryotic and thus have a nucleus so other parts of the viral replication process will be different from phages. Another big difference is that many of the animal viruses bud out of the host cell so they will have an envelope which comes from the cytoplasmic membrane of the host cell.

When animal cell gets infected with a virus what are the possible consequences? How can a virus cause cancer?

- The possibilities are persistent infections in which the virus buds out of the host without lysing the host. Latent infections are when the virus enters the host chromosome and are known as proviruses and can go into lytic cycle. When the viral DNA incorporates into the host chromosome it can also cause a mutation that results in a transformation of the host cell into a tumor or cancer cell. Normal cells have contact inhibition in which they grow to a certain density and then stop. Tumor cells lack contact inhibition and thus continue to reproduce and make tumors.

What is a capsid, capsomere, nucleocapsid, envelope and naked virus?

- capsid: a protein shell that surrounds the genome of a virus particle (composed of a number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid) - capsomere: subunit of the capsid (smallest morphological unit visible with an electron microscope) - nucleocapsid: complete complex of nucleic acid and protein packaged in the viron - enveloped virus: virus that contains additional layers around the nucleocapsid - naked virus: virus that does not contain additional layers around the nucleocapsid

What are capsids made of? Viral envelopes?

- capsids are omposed of a number of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid (capsomere smallest subunit) - the envelope comes from the host cell cytoplasmic membrane so it is a lipid bilayer (and proteins). The envelope may contain proteins that are called spikes as in the case of the influenza virus.

What types and arrangements of nucleic acids are found in viruses?

- either DNA or RNA genome - some are circular, but most are linear - single- stranded or double- stranded

What is a host? bacteriophage?

- host: a cell inside which a virus replicates - bacteriophage: viruses that infect bacteria (ex: lambda and T4)

How is a provirus different from a prophage?

- provirus: the genome of a temperate or latent animal virus when it is replicating in steps with the host chromosome (animal) - prophage: the lysogenic form of a bacteriophage (bacteria) - Unlike a prophage, the provirus never comes out of the chromosome. Sometimes the provirus simply remains in a latent state and replicates when the DNA of the host cell replicates. In other cases, the provirus is expressed and produces new viruses, which may infect adjacent cells.

Describe a complex virus and give an example.

- virions composed of several parts, each with separate shapes and symmetries - Bacterial viruses contain complicated structures (Icosahedral heads and helical tails) - Bacteriophage T4 of Escherichia coli

What keeps temperate phages latent?

cI protein (the lambda repressor): causes repression of lambda lytic events

What units are used to measure viruses?

nanometers