Virus - Answers non-cellular, non-living infectious agent with its own genome. They are obligate
intracellular parasites.
Virus components - Answers 1. Genomic material
2. Capsid
Capsid - Answers membrane-like protein structure containing the virus's genetic material (similar to a
cell's nucleus)
Envelope - Answers an additional outer membrane surrounding the capsid, derived from the host cell's
plasma membrane taken as virus "buds" from host cell. Found in a majority of animal viruses.
Naked virus - Answers non-enveloped; host cell bursts as virus lyses from cell. Majority of
bacteriophages.
Paramyxovirus - Answers Enveloped, 100-150 nm diameter, spherical. Single stranded linear genome
fuses with the host cell membrane to initiate entry and replication. (Measles and mumps)
Orthomyxovirus - Answers Similar to paramyxovirus but contains eight segments of RNA and enters the
host via endocytosis (influenza)
Number of viruses known to infect mammals - Answers 5,000
Number of viruses known to infect humans - Answers 220
Estimated number of uncharacterized viruses - Answers 300,000
Virion - Answers a single virus particle with a capsid and genetic material
Viral spikes - Answers glycoprotein extensions that identify and bind to host cell proteins. Can be
changed by mutating genomes
Purpose of viral genome - Answers To encode proteins necessary for capsomere, spikes, and enzymes
for replication
DNA viral genome - Answers -Can be circular or linear
-Often double stranded
-May be single stranded
RNA viral genome - Answers -Can be linear or segmented
, -Often single stranded
-May be double stranded
Human genome size - Answers 3 billion base pairs; 25,000 genes
Viral genome size - Answers 7700-2.5 million base pairs; 300 genes
Central dogma of biology - Answers DNA is transcribed into mRNA, which is translated by ribosomes into
making proteins
Protein encoding for double-stranded viral DNA - Answers Same as for cells; DNA-->transcription--
>mRNA-->protein
Protein encoding for single-stranded viral DNA - Answers Complementary DNA is built-->transcription--
>mRNA-->protein
Protein encoding for ssRNA+ viruses - Answers mRNA-like genome is immediately ready for translation.
(polio, rubella, West Nile encephalitis)
Protein encoding for ssRNA- viruses - Answers Genome is complementary to mRNA. Transcription by
RNA-dependent RNA polymerases-->mRNA-->proteins (influenza, measles, ebola, rabies)
Protein encoding for retroviruses - Answers mRNA-like genome is converted to DNA form by reverse
transcriptase--->DNA is inserted in host cell's genome-->transcription-->mRNA-->protein (HIV)
Protein encoding for dsRNA viruses - Answers Double-stranded RNA is unwound by RNA-dependent RNA
polymerase to single-stranded mRNA-->protein
Viral replication - Answers When virus uses the host cell's resources (amino acids, nucleotides, enzymes,
and organelles) to make new virions
6 steps to viral replication - Answers 1. Attachment
2. Entry
3. Uncoating
4. Replication
5. Assembly
6. Release
Attachment - Answers Virus attaches to host cell via capsid proteins for naked viruses or spike proteins
for enveloped
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