Microbiology by Body System - Bauman - Ch 13 Objectives

13.7 - Sketch and describe the five stages of the lytic replication cycle as it typically occurs in bacteriophages.

1. Attachment of the virion to the host cell. 2. Entry of the virion to the host cell. 3. Synthesis of new nuclei acids and viral proteins by the host cells enzymes and ribosomes. 4. Assembly of new virions within the host cell. 5. Release of the new virion from the host cell.

E. coli phage T4 replication:

1. Attachment: structure responsible for attachment is its host bacterium are its r=tail fibers. Attachment is dependent on the chemical attraction and precise fit between attachment proteins on the phages tail fibers and complementar receptor proteins o the surface of the host cell wall. The specificity of the attachment proteins for the receptors ensures that the virus will attach only to E.coli. 2. Entry: T4 releases lysozyme: a protein enzyme carried within the capsid that weakens the peptidoglycan of the cell wall. The pahges tail sheath then contacts, forcing an internal hollow tube within the tail through the tube and into the bacterium. The empty capsid is left on outside of the cell looking like abandoned spacecraft. After entry, viral enzyme degrades the bacterial DNA into its constituent nucleotides. 3. Synthesis: after losing its chromosomes, the bacterium stops synthesizing its own molecules and begins synthesizing new viruses under control of the viral genome. For dsDNA viruses like T4, protein synthesis is straight-forward and similar to cellular transcription and translation, except that mRNA is transcribed from viral DNA instead of cellular DNA. 4. Assembly: appears that capsomeres accumulate within the cell, they spontaneously attach to one another to form new capsid head. Tails assemble and attach to heads and tail fibers attach to tails forming mature virions. 5. Release: newly assembled virioins are released from the cell as lysozyme completes it works on the cell wall and the bacteria disintegrates. For phage T4, the process of lytic replication takes about 25 minutes and can produce as many as 100 to 200 new virions for each bacterial cell lysed.

13.2 - Explain the mechanism by which viruses are specific for their host cells.

Due to the precise affinity of viral surface proteins or glycoproteins for complementary proteins or glycoproteins on the surface of the host cell.

13.3 - Compare and contrast viruses of fungi, plants, animals and bacteria.

Fungi: • The fungal virus only exist within the cell. They have no extracellular state. But fungal viruses can't penetrate a thick fungal cell wall, however because fusion of cells is typically part of fungal cycle, viral infections easily be propagated by fusion of infected fungal cell with uninfected one. Plants: • Enter either through abrasions of the cell wall or by plant parasites, such as nematodes and aphids. • After entry, plant viruses follow the replication cycle. Animal: animal viruses use a variety of strategies depending on their nucleic acid; DNA or RNA, double stranded or single stranded.

13.1 - Discuss viral genomes in terms of dsDNA, ssDNA, ssRNA, dsRNA, and number of segments of nucleic acid.

Genome of every cell is double-stranded DNA, the genome of a virus may be either DNA or RNA. Some viral genomes are doubled stranded DNA (dsDNA), like genomes of cells. Other viruses use single-stranded RNA (ssRNA), single-stranded DNA (ssDNA) or double stranded RNA (dsRNA). Genomes of any particular virus may be either linear and composed of several molecules of nucleic acid, as in eukaryotic cells or circular and singular, as in most prokaryotic cells.

13.11 - Compare and contrast the release of viral particles by lysis and budding.

In budding, as virions are assembled, they are extruded through one of the cells membranes (ER or cell membrane). Virion acquires part of membrane, uses as envelope. In lysis, is quick with bacteriaphages. In animal cells' budding, host cell allows infected cell to remain alive for some time. Persistent infections: infection with envelope viruses in which host cells shed viruses slowly and relatively steady.

13.24 - Compare and contrast prions and viruses.

Prions require incineration or autoclaving in NaOH

13.23 - Define and describe prions, including their replication process.

Prions: proteinaceous infective particles lacks instructional nucleic acid Encourages molecules with normal PrP (cytoplasmic membrane protein) to refold into prion PrP which then clump together.

13.6 - List the characteristics by which viruses are classified.

Their type of nuclei acid, presence of an envelope, shape and size. Nucleic Acid (primary method): dsDNA, ssDNA, dsRNA, ssRNA. Shape: Helical: composed of capsomeres that bond together in a spiral fashion to form a tube around the nucleic acid. Polyhedral: is roughly spherical, with a shape similar to geodesic dome. Complex viruses: have capsids of many different shapes that don't readily fit into either of the two categories. The complex shapes of many bacteriophages include icosahedral heads, which contain the genome, attached to helical tails with tail fibers. Envelope: Envelope virion: virus with an envelope Naked envelope: virion without an envelope (Virus gets envelope from its host cell during viral replication or release. • The envelope of a virus is a portion of the membrane system of the host cell. Host DNA carried the genetic code required for the assembly of the phospholipids and some of the proteins in the envelop, while the viral genome specifies the other membrane proteins. The viral envelop doesn't perform other physiological roles of a cytoplasmic membrane, such as endocytosis or active transport. An envelope proteins and glycoproteins often play a role in recognition of host cells.) Size: Linear and composed of several segments, or single and circular.

13.21 - Define and describe viroids.

Very small, circular pieces of RNA that are infectious and pathogenic in plants.

13.22 - Compare and contrast viroids and viruses.

Viroids lack capsids. Still circular, appear linear. Viroids infect plants.

13.9 - Explain the differences between bacteriophage (lysogenic) replication and animal viral replication.

What is Lysogeny (replication)? this is when the host cell continues to grow and reproduce with the virus for many generations before lysis. What happens during Genome Insertion (lysogeny)? the virus is inactive - prophage - does not degarde host cell DNA but becomes incorporated into host cell DNA. What happens during Genome Replication (lysogeny)? the host cell replicates the prophage DNA along with its own DNA which it passes onto daughter cells - so that all daughter cells are infected. What is Lysogenic Conversion (lysogeny)? changing the phenotype of bacterium by lysogenic phage; may convert harmless bacterium into pathogen. What happens during Induction (lysogeny)? excision of prophage from host cell DNA by Inductive Agents, UV, xrays, Carcinogenic chemicals. What is the final outcome of Lysogeny? the host cell synthesizes the virus DNA within its own DNA, an assembly of new virions within the host cell, lysis of the host cell and spillage of the new virions from the dead host cell. How do Animal Virus replicate? basically the same replication pathway as bacteriophages (attachment, entry, synthesis, assembly, and release). What are some differences in Animal Cell virus replication? presence of an envelope around some animal viruses, the eukaryptic nature of animal cells and the lack of a cell wall in animal cells. How do Animal Cell viruses attach? there is a chemical attraction between viral proteins or glycoproteins on virion and complementary cell receptors on animal cell's cytoplasmic membrane. What are some characteristics of Animal Cell viruses? they do not have tails or tail fibers, they have glycoprotein spikes or other attachment molecules that mediate attachment. What is Direct Penetration (animal virus entry)? viral capsid attaches to and sinks into host cytoplasmic membrane, forming a pore through which viral genome alone enters the cell; example naked viruses - poliovirus and dengue fever. What is Membrane Fusion (animal virus entry)? viral envelopes fuses with host cell membrane and releases capsid into cell; measles and mumps. What is Endocytosis (animal virus entry)? virus attaches to host cell membrane receptors which stimulate host cell to endocytizes entire virus; herpesviruses. How is synthesis of animal viruses different? animal viruses use a variety of strategies depending on their nucleic acid; DNA or RNA, double stranded or single stranded.

13.25 - List four diseases caused by prions.

bovine spongiform encephalitis sheep scrapie kuru chronic wasting disease variant Creutzfeldt Jakob disease

13.4 - Discuss the structure and function of the viral capsid. 13.5 - Discuss the origin, structure, and function of the viral envelope.

• Capsid: protein coat that surrounds nucleic acid and provides protection for viral nucleic acid and a means of attachment to a host cell; composed of capsomeres. • Envelope (sometimes present): phospholipid membrane that surrounds the capsid. • The outermost layer of a virion provides the virus both protection and recognition sites that bind to complementary chemicals on the surface of their specific host cell. Once a virus is inside, the intracellular state is initiated, and the capsid is removed. Virus without its capsid exists solely as nucleic acid but still referred to as a virus. • Virion: outside the cell • Virus: inside the cell • Virus gets envelop from its host cell during viral replication or release. • The envelope of a virus is a portion of the membrane system of the host cell. Host DNA carried the genetic code required for the assembly of the phospholipids and some of the proteins in the envelope, while the viral genome specifies the other membrane proteins.

13.12 - Compare and contrast latency in animal viruses with phage lysogeny.

• Latency: the virus will have not viral activity or signs or symptoms for years. • Proviruses (latent virus): inactive cell in an animal cell. May not become part of host cell genome whereas always does with lysogeny and is permanent when in animal cell as induction does not occur in eukaryotes.

13.20 - Discuss aspects of viral replication that are lifelike and non-lifelike.

• Living things must have: Growth, self-reproduction, responsiveness, ability to metabolize, and contain cells. • Viruses can sophisticated methods to invade cells, can control host cells, have genome containing instructions for replication themselves. However, a virus is dependant on hosts' organelles and enzymes to produce new virions.

13.8 - Compare and contrast the lysogenic replication cycle of viruses with the lytic cycle.

• Lysogenic cycle: process of viral replication in which a bacteriophage enters a bacterial cell, inserts into the DNA of the host, and remains inactive. The phage is then replicated every time the host cells replicate its chromosome. Later the phage may leave the chromosome. • Lytic replication: process of viral replication consisting of 5 stages ending with lysis of and release of new virions from the host cell. • Another difference: is that prophage is inserted onto the DNA of the bacterium, becoming a physical part of the bacterial chromosome.

13.10 - Compare and contrast the replication and synthesis of DNA, -RNA and +RNA viruses.

• Retrovirus (eg HIV) use DNA intermediary that's transcribed from +RNA by reverse transcriptase carried within the capsid. Don't use their genome as mRNA. +RNA can be directly translated by ribosomes to translate protein. -RNA is transcribed to serve as template for more +RNA. +RNA can become part of host cell's genome. • Most DNA viruses assemble in and are released from the nucleus into the cytosol, whereas most RNA viruses develop solely in the cytoplasm. (DNA double-stranded RNA single-stranded, some DS)