BIOS 390 Exam 2 - Not cellular 2. Obligate intracellular parasite...

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BIOS 390 Exam 2

• Virus

–Answer Latin for poison (Pasteur) Not living Not cellular

• Obligate intracellular parasite

–Answer Perform no metabolism Can not freely reproduce No protein synthesis Carry no or few enzymes

• Naked virus (non-enveloped virus) anatomy

–Answer

–Answer Genetic material (DNA or RNA) Capsid-protein coating (composed of capsomere proteins)

• Enveloped virus anatomy

–Answer

–Answer Genetic material (DNA or RNA) Capsid Envelope - phospholipid bilayer Spikes (often) - virally-encoded membrane proteins

• Complex viruses

–Answer

–Answer Example –Answer poxviruses - DNA surrounded by layers of lipopro- teins 1 / 4

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Example –Answer T4 Bacteriophage - DNA or RNA surrounded by capsid, helical protein tail, tail fibers

• Classifications

–Answer International Committee on the Taxonomy of Viruses (ICTV)-

–Answer 1.) Nucleic acid type (single-stranded or double-stranded DNA; single-stranded or double- stranded RNA) 2.) Replication process 3.) Morphology (envelope, capsid type, etc.) 4.) Effects Commonly used –Answer Family, Genus, species (common name) –Answer Picornaviridae, En- terovirus, Polio virus

• Viral multiplication

–Answer Absorption (attachment) Penetration/uncoating Replication (biosynthesis) Assembly/maturation Release (budding or lysis)

• Viral host range

–Answer Types of cells within a host species which can be infected by the virus Determined by attachment (susceptible) and cellular components necessary for viral replication processes (permissive).

• Bacteriophage multiplication 2 / 4

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–Answer

–Answer 1.) Attachment - phage attaches to host cell.

2.) Penetration - phage penetrates host cell and injects its DNA.

3.) Biosynthesis - phage DNA directs synthesis of viral components by the host cell.

4.) Maturation - viral components are assembled into virions 5.) Release - host cell lyses and new virions are released.

• Animal viruses

–Answer Variations on the same 5 basic viral multiplication steps based on –Answer

Genetic material Surface structures Enzymes of virus and/or host cell

• DNA animal virus

–Answer 1.) Virion attaches to host cell.

2.) Virion enters cell, and its DNA is uncoated 3.) A portion of viral DNA is transcribed, producing mRNA that encodes "early" viral proteins.

4.) Viral DNA is replicated, and some viral proteins are made.

5.) Late translation; capsid proteins are synthesized.

6.) Virions mature.

7.) Virions released.

• RNA viral multiplication (ssRNA; + or sense strand; Picornaviridae)

–Answer 1.) Attachment 2.) Entry and uncoating. Uncoating releases viral RNA and proteins.

3.) RNA replication by viral RNA-dependent RNA polymerase. - strand is transcribed from + 3 / 4

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viral genome. mRNA is transcribed from the - strand.

4.) Translation and synthesis of viral proteins.

5.) Maturation and release.

• RNA viral multiplication (ssRNA; - or antisense strand; Rhabdoviridae

–Answer 1.) Attachment.

2.) Entry and uncoating. Uncoating releases viral RNA and proteins.

3.) RNA replication by viral RNA-dependent RNA polymerase. The + strand (mRNA) must first be transcribed from the - viral genome before proteins can be synthesized. Additional - strands are transcribed from mRNA.

4.) Translation and synthesis of viral proteins. - strands are incorporated into capsid.

5.) Maturation and release

• RNA viral multiplication (dsRNA; + or sense strand with - or antisense strand, Reoviridae

–Answer 1.) Attachment 2.) Entry and uncoating. Uncoating releases viral RNA and proteins.

3.) RNA replication by viral RNA-dependent RNA polymerase. mRNA is produced inside the capsid and released into the cytoplasm of the host.

4.) Translation and synthesis of viral proteins. RNA polymerase initiates production of - strands. The mRNA and - strands form the dsRNA that is incorporated as new

viral genome.

5.) Maturation and release.

• Retroviral multiplication

–Answer enveloped RNA –Answer Two identical + strands of RNA 1.) Retrovirus enters by fusion between attachment spikes and the host cell recep- tors.

2.) Uncoating releases the two viral RNA genomes and the viral enzymes reverse transcriptase, integrase, and protease.

3.) Reverse transcriptase copies viral RNA to produce double-stranded DNA.

4.) The new viral DNA is transported into the host cell's nucleus, where it is integrated into a host cell chromosome as a provirus by viral integrase. The provirus may be replicated when the host cell replicates.

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