Microbiology: Viruses and Prions

Vocabulary terms and definitions from microbiology lecture notes covering viral anatomy, replication cycles, latency, retroviruses, cytopathic effects, and prion diseases.

Capsid

The outer protein coat of a virus made up of individual protein subunits called capsomeres.

Nucleocapsid

The viral structure composed of the viral genome packaged together with its protein capsid.

Virion

The complete, infective extracellular form of a virus that exists outside of a host cell.

Viroid

An infectious agent / virus that specifically infects plant cells.

Helical Capsid

A capsid structure where capsomeres are arranged helically around nucleic acid, giving the virus a rod-shaped appearance.

Isometric (Icosahedral) Capsid

A capsid structure where capsomeres form a shell around nucleic acid with faces composed of equilateral triangles.

Bacteriophage Structure

A complex virus structure consisting of an icosahedral head enclosing viral DNA, attached to a neck, collar, tail sheath, base plate, and tail fibers.

Viral Envelope

A outer membrane composed of a phospholipid bilayer acquired by certain viruses that surrounds the nucleocapsid.

Viral Spikes

Proteins on the exterior surface of a virus responsible for binding to specific receptors on a host cell.

Lytic Cycle

A bacteriophage replication pathway consisting of attachment, entry/penetration, synthesis of viral components, assembly/maturation, and lysis of the host cell for phage release.

Lysogenic Cycle

A viral life cycle in bacteriophages where viral DNA integrates into the host bacterial chromosome without immediately assembling or releasing new phages.

Prophage

Bacteriophage DNA that is incorporated into the bacterial host chromosome.

Induction

The process by which a prophage excises from the bacterial chromosome to initiate the lytic cycle, typically occurring when the bacterium becomes sick or stressed.

Direct Penetration

A mechanism of entry for certain nonenveloped animal viruses in which the viral capsid binds to host receptors and injects the viral genome directly across the cytoplasmic membrane.

Uncoating

The process of separating the viral nucleic acid from its protective protein capsid inside the host cell.

Budding

The release mechanism used by enveloped viruses where the capsid pushes out through the host cytoplasmic membrane, taking host membrane lipids and viral glycoproteins to form an envelope.

Latent Virus

A virus that remains dormant within host tissues for extended periods but can periodically reactivate to produce active infection.

Herpes Simplex Virus Type 1 (HSV-1) Latency

A condition where HSV-1 travels up the trigeminal nerve following oral cold sores or fever blisters to remain dormant in sensory ganglia until reactivated by factors like menstruation, fever, sunburn, or stress.

Reverse Transcriptase

A retroviral enzyme that transcribes single-stranded viral RNA into double-stranded DNA ($\text{dsDNA}$).

Provirus

Viral DNA integrated permanently into a eukaryotic host cell's chromosome, remaining protected from the host's immune system.

Oncogenic Viruses

Viruses that infect eukaryotic cells and alter their genetic material with the potential to transform a normal cell into a cancerous cell.

Persistent Viral Infection

A chronic infection where a virus does not kill host cells immediately, but slowly produces virions over months or years until the cells eventually die.

Cytopathic Effect (CPE)

Observable microscopic changes or damage induced in host cells as a result of viral infection.

Syncytia

Giant multinucleated host cells formed by the fusion of multiple infected adjacent cells, representing a cytopathic effect of certain viruses.

Negri Bodies

Distinct intracellular inclusion bodies formed within the cytoplasm of infected neurons as a cytopathic effect.

Prion

A proteinaceous infectious particle consisting of an abnormal protein ($\text{PP}$) that binds to and converts normal prion proteins ($\text{NP}$) into abnormal pathogenic conformations.

Chronic Wasting Disease

A prion disease affecting cervids, including white-tailed deer, black-tailed deer, mule deer, elk, reindeer, and moose.

Scrapie

A fatal neurodegenerative prion disease that affects sheep.

Bovine Spongiform Encephalopathy (BSE)

A transmissible spongiform encephalopathy in bovines, also known as Mad Cow disease, which can be transmitted to humans as New Variant CJD.

Creutzfeldt-Jakob Disease (CJD)

A human prion disease that occurs spontaneously at a rate of 1 out of every 1 million people.

Kuru

An extinct prion disease of humans in Papua, New Guinea, that was spread through the practice of cannibalism.

HIV Structural Proteins

Key proteins of Human Immunodeficiency Virus, including envelope surface glycoproteins ($\text{env gp120}$ and $\text{env gp41}$), matrix protein ($\text{gag p17}$), and capsid protein ($\text{gag p24}$).

you can see viruses with a light microscope (true or false)

true

Viruses can contain both RNA and DNA (true or false )

true

do viruses undergo mitosis

No, viruses do not undergo mitosis as they are not cellular organisms; they require and living host to grow(acellular)

what makes a virus host specific

Spike proteins ( are specific for attaching to a specific receptor on host cell

Name the 5 stages of the replication cycle in viruses

1. Attachment

2. Entry

3. Synthesis

4. Replication

5. Release

How do these stages differ in bacteriophage vs. animal viruses

Bacteriophages only replicate through lytic or lysogenic replication

Naked virus

a virion without an envelope

Capsomere

individual protein units that make up the capsid

3 viruses that can cause congenital defects

1. rubella virus

2. cytomegalovirus

3. herpes virus

what word is used to cause congenital defects

teratogenic

what is a bacteriophage

a type of virus that only infects bacterial cells

Generalized transduction

the transducing phage carries random DNA segment from a donor host cells chromosomes or plasmids to a recipient host cell.

Specialized transduction

only certain host sequences are transferred

Name two viruses that can cause cancer

1.Epstein Barr viruse

2.papilloma virus

What word is used to describe viruses that cause cancer

Oncogenic

How is a virus similar to chlamydia

they are both intracellular parasites

3 shapes seen for capsids

1. helical

2. isometrical(polyhedral)

3. pleomorphic

what is a spike and where does it come from

its a projection of the envelope or capsid and is make of glycoproteins for attachment to the host cell

How does an animal virus obtain its envelope

during budding it gets its envelope from its host’s cells membrane

describe the steps for the steps in the lytic cycle

1. Attachment

2. entry

3. metabolism

4. assembly

5. release

name the steps of the lysogenic cycle

1. attachment

2. entry

3. prophage

Describe the productive cycle for animal viruses

results in active replication and release of new virus particles usually killing the host cell

describe the latent cycle for animal viruses

involves the virus remaining dormant inside the host cell without producing new virions

How are viruses cultured and grown?

Can be cultured but must be cultured inside a suitable host

What is meant by a cytopathic effect

can be used by virologist to determine type of viral infection

Name two examples of cytopathic effect

1. Rabies virus (negri bodies)

2. Respiratory syncytial virus (syncytia)

A complete virus particle is called a(n)

virion

Most enveloped viruses gain entrance into the host cell by _____ of the viral envelope with the _____

Fusion; host cell membrane

name a human disease believed to caused by a prion

Creutzfeldt-Jakob disease (CJD)

Name a virus that contains reverse transcriptase

retrovirus

Why is reverse transcriptase such an important enzyme

it converts single stranded RNA into double stranded DNA which is important for retroviral reproduction

Name two viruses that cause latent infections

HSVI, HSVII, varicella-zoster virus(chicken pox)

What is the basic difference between acquired and innate immunity?

Acquired is against one type of antigen only and innate is against ANY invader

What is the mucociliary escalator?

its system that uses mucus to push any trapped particles upward.

What is the function of lysozome and where is it made

Can break down cell walls; white blood cells(neutrophils/ macrophages)

Which white blood cells can phagocytize bacteria

Neutrophils, monocytes, macrophages

Which white blood cells phagocytizes antigen-antibody complexes

Eosinophils

which white blood cell can kill all kinds of abnormal body cells directly

Natural killer cells (NK cells)

Where is complement found?

In the blood plasma