BIO 302 Quiz 6 - Virus Only Info

Are viruses cells?

No, they non-living and acellular

How small are viruses?

They are smaller than bacteria and require electron microscopy to be seen

Fill in the blank
___ require a host cell for their replication, some have strange schemes for nucleic acid synthesis.

Viruses

What is a virion

a virus particle

What is a bacteriophage?

they are viruses that targets bacteria

What do all viruses have?

genome: DNA or RNA; double- or single-stranded
capsid - protein coat
-capsomers - individual subunits that comprise the capsid
-capsomers self-assemble into a capsid

What are things that only some viruses have?

envelope - lipid bilayer derived from host cell membrane during viral budding
• note: virtually all bacteriophage are naked; animal viruses can be enveloped or naked
spikes - viral proteins or glycoproteins in the envelope
(enzymes - for replication or pathogenesis)

What are the two common viral shapes?

icosahedron and helical

How are the 3 ways viruses classified?

by host (bacteriophage vs. animal viruses)
by genome type (DNA vs. RNA / single vs.double stranded / positive vs. negative strand RNA)
enveloped vs naked (nonenveloped)

What are the stages of the lytic replication cycle of a bacteriophage?

1.) Attachement (adsorption)
2.) Penetration (injection)
3.) Synthesis of nucleic acid and protein
4.) Assembly and packaging
5.) Release (lysis)

What are the stages of the lysogenic replication cycle of a bacteriophage?

1.) Attachement (adsorption)
2.) Penetration (injection)
3.) Prophage integration

What happens during the attachment (adsorption) stage of Viral replication?

-ligands on viruses bind to receptors on host cells

-ligands may be on spikes or capsid proteins

-highly specific; a virus can’t just infect any cell.

What happens during the penetration stage of Viral replication to bacterial cells?

-release of the nucleic acid from the capsid

-phage: usually inject genome into bacterial cell, leaving capsid outside

What happens during the penetration stage of Viral replication to animal cells?

-animal viruses enter cells by fusion or endocytosis, or both

What does positive strands indicate about a virion?

The virion’s RNA can directly serve as mRNA

What does negative strands indicate about a virion?

The virion’s RNA must first be copied into a complementary strand, which then serves as mRNA.

dsDNA and ssDNA viruses:

can use host enzymes to make new viral genomes

dsRNA and ssRNA viruses:

need RNA replicase enzyme (RNA- dependent RNA Polymerase) to make new viral genomes

-RNA replicase enzyme must be carried in the virion in a negative (-) strand RNA virus

retrovirus:

positive (+) strand ssRNA genome but uses a dsDNA intermediate

-carries the enzymes reverse transcriptase and integrase

-DNA intermediate integrates into host genome

Would you expect a bacterium or a virus to have more genes? Why?

You would expect a bacterium to have significantly more genes than a virus. A typical bacterium like Escherichia coli has roughly 4,000 to 4,500 genes to encode all the machinery required for things like metabolism, energy generation, nutrient uptake, etc. Viruses have less genes because they are are acellular infectious agents that lack their own metabolic machinery. They cannot generate ATP, synthesize proteins independently, or carry out metabolic reactions.

What are some genes you would expect to find in a virus?

Structural Genes like Capsid Protein Genes and Envelope / Spike Glycoprotein Genes. Replication and Enzymatic Genes. Virulence factors.

Why are virtually all phage naked? (e.g. why don’t they have envelopes?)

The Rigid Bacterial Cell Wall Blocks Budding
Phages Exit via Lysis, Not Budding
Naked phages rely solely on a sturdy protein capsid, which is exceptionally rugged and allows them to survive harsh environmental conditions until they find a new bacterial host.