Microbiology - Ch. 13 Viruses, Viroid's, and Prions. - flashcards

What's the size range of viruses, and what unit are they measured in vs. bacteria?

Wide range but very small — measured in nanometers (nm).

Bacteria are measured in micrometers (µm). nm << µm < mm.

Are prions and viroids viruses? What size are they roughly?

No — prions (~200×20 nm) and viroids (~300×10 nm) are not viruses, though similarly tiny.

How is viral structure unique — cell status and nucleic acid?

Acellular (no cell membrane/cytoplasm); not Prokaryote or Eukaryote (no Domain/Kingdom). Contains only ONE nucleic acid type — DNA or RNA, never both.

What are the 4 structural components of a typical virus (inner vs outer)?

Core (inner — DNA or RNA). Capsid (surrounds core, made of capsomeres). Envelope & Spikes (outer, both optional). No envelope = "naked virus."

Where do viruses multiply, and what does that make them?

Inside living host cells → "obligate intracellular parasites." They don't reproduce — no binary fission or mitosis.

What is host specificity, with examples?

Viruses have a specific host range — plant virus attacks plant cells, animal virus attacks animal cells, bacteriophage attacks bacteria.

What is tissue specificity, with examples?

Viruses infect specific tissue — e.g., animal virus causes viral hepatitis (liver) or viral encephalitis (brain).

How are viruses transmitted?

Various modes — air, food/water, direct contact, insects.

What does "phage" mean, and what is a bacteriophage?

"Phage" = virus. A bacteriophage is a bacterial virus, whose host cell is a bacterium.

What is phage DNA, and whose DNA is it considered to be?

Phage DNA is viral DNA — it belongs to the virus, not the bacterium.

What is capsid architecture, and what are the 3 virus types based on it?

Capsid shape (structure) that protects the genetic core (DNA/RNA). Types: helical, polyhedral, complex viruses.

What's unique about complex viruses, and what's an example structure (exam figure)?

Complex viruses only exist as bacterial viruses (e.g., T-even bacteriophage — Fig 13.5a). Structure includes capsid head, core (DNA), sheath, tail fibers.

What is viral taxonomy used for, and why is there no Domain/Kingdom?

Classification for identification purposes. No Domain or Kingdom because viruses aren't cells.

What are the viral taxon levels (highest to lowest) with naming conventions and examples?

Family (-viridae, e.g. Herpesviridae) → Genus (-virus, e.g. Enterovirus) → Species (lowest taxon; group sharing similar genetic info & host, e.g. HIV/SIV — SIV found in primates).

Are subspecies/strains an official taxon? Give examples.

No — not an official taxon. Examples: HSV-1, HSV-2 (both Herpes simplex virus), Influenza H1N1, H5N1.

How are bacteriophages grown, and what do they form?

Grown in bacteria (live host cell). Form plaques — clear spaces of cell damage on a "bacterial lawn," each corresponding to a single virus. Measured as plaque-forming units (PFU), vs. CFU for bacteria colonies.

Can bacteriophages grow in animal cells?

No — due to host specificity.

How are animal viruses grown, and how is infection detected?

Grown in living animals, embryonated eggs, or animal tissue cultures (animal virus injected into live animal host cell). Infection detected via cytopathic effect (CPE) — visible deterioration/damage to the host cell.

Can animal viruses grow in bacterial cells?

No — due to host specificity.

What are the 3 methods of virus identification?

CPE (damage type to animal host cell), serological tests (blood test looking for antibodies — most common method), PCR (isolate viral DNA → make many copies → identify virus).

Why do we say viruses "multiply" rather than "reproduce," and what does this involve?

Prokaryotes/Eukaryotes reproduce (binary fission/mitosis);

Viruses can't — they're obligate intracellular parasites that must invade a living host cell and hijack its metabolic machinery, forcing it to (1) make viral parts and (2) assemble them.

What are the 2 cycles of bacteriophage multiplication?

1. Lytic cycle (required — phage causes lysis/death of bacterial host cell).

• Lysis = host cell ruptures, releasing the newly made virions so they can’t infect other cells.

2. Lysogenic cycle (optional/not required — phage does NOT kill host cell; instead phage DNA incorporates into the bacterial host cell's DNA, and the host cell divides normally).

What are the two paths a bacteriophage can take to multiply?

Option 1: enter and complete lytic cycle only → host cell death.

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Option 2: enter and complete lysogenic cycle first (dormant) → later re-enter and complete lytic cycle → host cell death. Either way, lytic cycle is always the final step that ends in host cell death.

What are the 5 stages of the bacteriophage lytic cycle (APBMR)?

1. Attachment (to bacterial host cell) →

2. Penetration (of phage DNA into host cell) →

3. Biosynthesis (making viral parts) →

4. Maturation (assembling viral parts) →

5. Release (of newly made virions from host cell — "lysis," leads to host cell death).

Identify this stage & describe key events for the next 5 cards (1):

Attachment — phage tail fibers attach to receptors on the bacterial cell wall. Viral lysozyme punches a hole so only viral DNA can enter (not the whole virus).

Identify this stage & describe key events for the next 5 cards (2):

Penetration — viral sheath contracts, pushing viral DNA into the bacterial host cell. Only phage DNA enters — capsid stays outside.

Identify this stage & describe key events for the next 5 cards (3):

Biosynthesis — viral DNA incorporates into bacterial host DNA, forming "hybrid" DNA. This forces the host cell to make viral components (e.g., capsomeres, tail fibers) via transcription & translation.

Identify this stage & describe key events for the next 5 cards (4):

Maturation — viral components get assembled into virions, newly-made mature viruses capable of infecting other cells.

Identify this stage & describe key events for the next 5 cards (5):

Release — bacterial host cell lyses when new virions are released, resulting in death of the host cell.

What is lysogeny, and what happens to the bacterial host cell?

Phage DNA integrates into and remains dormant in the bacterial host cell as "hybrid DNA" called a prophage — phage particle production is delayed (biosynthesis hasn't started yet). The host cell does NOT die; it divides by binary fission, replicating the prophage along with its own DNA (many prophages present).

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Summary: lysogeny = the virus going undercover inside the host's DNA and riding along for free, instead of immediately killing the cell

What 3 things does lysogeny alter about the host cell's characteristics?

1. Phage conversion — non-pathogenic bacteria become pathogenic.

2. Latent viral infection — virus "hides out" inside the host cell.

3. Transformation — virus turns on cancer-causing genes.

What is a prophage, and how does it form?

Phage injects its viral DNA into the bacterial cell → viral DNA integrates into the bacterial chromosome, forming one hybrid DNA strand → this hybrid DNA is called a prophage. When the bacterium divides (binary fission), the prophage gets copied and passed to daughter cells.

What 3 things does lysogeny alter about the host cell's characteristics?

1. Phage conversion — non-pathogenic bacteria become pathogenic (phage carries toxin genes)

2. Latent viral infection — virus "hides out" in tissue like the nervous system (e.g., shingles, herpes/cold sores/genital herpes)

3. Transformation — virus turns on cancer-causing genes

What are the two paths phage DNA can take after entering the bacterial cell, and how can it switch cycles?

1. Lytic cycle (make/assemble new virions → cell lyses (cell ruptures/dies virions released).

2. Lysogenic cycle (integrates as prophage → cell divides normally). Prophage can later excise and re-enter the lytic cycle.

What are the two multiplication options for the Lytic / Lysogenic cycle.

Multiplication option #1: (Lytic only)

A, P, B, M, R (Attachment, Penetration, Biosynthesis, Maturation, Release).

Multiplication option #2: (Lysogeny)

1. A + P

2. Lysogenic cycle

3. B, M, R

What are the 6 stages of animal virus multiplication (lytic cycle)?

1. Attachment.

2. Entry — by receptor-mediated endocytosis (RME) or fusion (entire virus enters host cell, unlike bacteriophages).

3. Uncoating — by viral or host enzymes to expose the genetic core (gets rid of capsid).

4. Biosynthesis.

5. Maturation.

6. Release — by budding or rupture.

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Steps #2 and #3 are unique to animal viruses.

Step #2 is analogous to penetration.

What are the two ways an animal virus enters an animal host cell?

1. Enveloped viruses enter by Fusion — viral envelope fuses with the animal host cell's plasma membrane.

2. Non-enveloped viruses enter by Receptor-Mediated Endocytosis (RME) — "engulfment."

What happens during Uncoating of an animal virus capsid, and what is the resulting hybrid DNA called?

After the virus enters the host cell, the protein capsid disintegrates to expose viral DNA. Viral DNA integrates into animal host DNA → hybrid DNA, called a provirus (vs. "prophage" in bacteria).

How does biosynthesis work once hybrid DNA (provirus) is formed?

Hybrid DNA → transcription → mRNA → translation → protein. This is how viral protein parts get made.

How does a DNA animal virus form a provirus?

Its DNA incorporates directly into the animal host cell's DNA, forming a provirus.

How does an RNA animal virus form a provirus, since RNA can't incorporate directly?

Its RNA is converted to DNA by reverse transcriptase, and that DNA then incorporates into the host cell's DNA to form a provirus. Ex: Retroviridae family (HIV) — has reverse transcriptase.

What's the full pathway from animal virus RNA to viral proteins?

Animal virus RNA → (reverse transcriptase) → animal virus DNA → incorporates into host DNA → "hybrid DNA" (provirus) → transcription → hybrid mRNA → translation → viral proteins.

When are viral protein particles made vs. assembled — what stages are these?

Made during Biosynthesis stage; assembled during Maturation stage.