BIOL 206 Exam 2

Obligate intracellular parasites

Pathogens that can only reproduce within a host cell.

Viruses

A type of obligate intracellular parasite that cannot reproduce or metabolize outside of a living host.

Inert macromolecules

The form viruses take outside of host cells.

Acellular

Term describing viruses, which are not composed of cells.

Viral genome

The genetic material of a virus, which can be made of DNA or RNA.

Types of viral genomes

dsDNA, ssDNA, dsRNA, ssRNA.

Size range of viruses

10 nm to 500 nm.

Protein capsid

A protective protein coat surrounding a viral genome.

Envelope

Some viruses have this structure surrounding the capsid.

Virus replication

The process by which viruses reproduce using the machinery of the host cell.

Size range of living cells

200 nm to 12 cm.

No ribosomes

Viruses cannot independently make protein products, as they do not possess ribosomes.

Herpes

The viral family that includes chicken pox and cold sores.

Electron microscope

The type of microscope needed to visualize viruses.

All viruses

The category of viruses that have capsids.

Capsid

The protein coat that surrounds a virus and protects its genome.

Capsomeres

Identical protein subunits that make up a capsid.

Nucleocapsid

The composite structure of the capsid and the nucleic acid of a virus.

Viral shapes

Filamentous/helical, icosahedral, enveloped, complex.

Filamentous/helical viruses

Flexible, curved, or coiled viruses, with a tubular continuous helix of capsomeres.

Icosahedral shape

A type of polyhedral shape characteristic of some viruses, having peplomeres.

Enveloped viruses

Viruses that must have spike proteins and bud out of a cell, includes COVID and herpes.

Envelope position

The envelope of a virus is located outside the nucleocapsid.

Function of an envelope

Helps a virus to evade the host immune system.

Infective envelope

An enveloped virus is not infective without its envelope.

Complex virus

A virus with a complicated structure, such as a bacteriophage.

Rabies nucleocapsid shape

Bullet shaped.

Species specificity of viruses

Viruses are typically specific to certain species due to protein interactions.

Conserved receptors

Receptors that are the same across different species, allowing viral transmission.

Bacteriophages

Viruses that cannot have an envelope due to bacterial cell walls.

Peplomeres function

Essential for infectivity and attachment of viruses.

Naked virus

A virus that does not have an envelope.

Viral envelope functions

Protection of nucleic acid, binding, and evasion of immune response.

Molecular mimicry

The resemblance between foreign and self-antigen, aiding viruses in disguise.

Attaching naked viruses

Naked viruses attach through peplomeres of their capsid.

Naked vs. enveloped virus resistance

Naked viruses are harder to kill on surfaces than enveloped viruses.

Environmental resilience

Enveloped viruses are harder to kill in the body than naked viruses.

Virion

A single virus particle.

Damage to cell membranes

Anything damaging cell membranes also damages viral envelopes.

Growing viruses media

Living cells must be used to grow viruses in the laboratory.

Animal virus growth methods

In living animals, embryonated eggs, or cell cultures.

Risk of growing viruses in living cells

Product contamination from the growth medium.

Phage exposure effect

Exposing lawns of bacteria to phages forms plaques.

Virus infection requirement

Viruses must interact with host cells to infect.

Virus motility

Viruses are non-motile.

Chemical attraction of viruses

Allows viruses to sense host cells.

Animal virus entry mechanisms

Direct penetration, membrane fusion, endocytosis.

Direct penetration process

The nucleic acid of a naked virus enters the host cell.

Membrane fusion process

Enveloped virus melts into the host cell's cytoplasmic membrane.

Endocytosis mechanism

Entire virus is taken into the cell upon binding with cell receptors.

Uncoating requirement

Upon entering an animal cell, viruses with a capsid must uncoat.

Budding/Blebbing process

Exocytosis method for enveloped viruses to exit the host cell.

Lysis definition

Process by which a cell bursts, releasing naked viruses.

Lysis from poxvirus releases

3,000 to 4,000 virions.

Lysis from poliovirus releases

Over 100,000 virions.

Budding process description

Spike proteins embed in the host membrane, the nucleocapsid binds inside, and then it pinches off.

Enveloped viruses and cells

Enveloped viruses can kill the cells they infect.

Phages entry to bacteria

Only the nucleic acid of phages can enter bacteria.

Phage exit method

Phages always exit a cell by lysis.

Viral host range definition

Refers to the number of species a virus can infect.

Rabies host range

Broad host range.

T4 bacteriophage host range

Narrow host range.

T4 phage infects

E. coli.

Five steps of phage replication

Adsorption/attachment, penetration, biosynthesis, maturation, release.

Adsorption/attachment phase

Phase where the virus binds to receptors of the host cell.

Penetration stage

Stage in which the viral genome enters the cell.

Biosynthesis stage

Production of viral components occurs during this stage.

Maturation phase

Assembly and completion of viral formation; happens spontaneously.

Release phase

Release of new virions by lysis of the host cell.

Burst time definition

Time from virus attachment to lysis.

Burst size definition

Number of viral particles released.

E. coli burst size

About 200 virions.

Enveloped virus replication differences

Enveloped viruses fuse into the cell and bud out, differing from naked viruses.

E. coli morphology

Gram-negative bacillus.

T4 phage lysozyme function

Weakens the cell wall of E. coli.

LPS of gram-negative bacteria role

Acts as binding sites for phages.

Lysogenic cycle description

Occurs when viral genome integrates into the host genome and replicates with it.

Lytic cycle description

Occurs when virus replicates into new virions and lyses the host cell.

Lysogenic to lytic cycle transition

Phages can switch from the lysogenic to lytic cycle.

Phage maturation stages

Base, tail, sheath, DNA, capsid, mature head, tail fibers formed in order.

Viruses crossing human genome

Only DNA viruses or retroviruses can cross into the human genome.

HPV definition

DNA virus associated with cervical, throat, and anal cancers.

Hepatitis virus

DNA virus that can lead to liver cancer.

DNA viruses and cancer

They can cause cancer when they crossover into oncogenes or DNA repair pathways.

Retroviruses function

Use reverse transcriptase to convert RNA into DNA.

MMR vaccine

Stands for measles, mumps, and rubella.

R naught (Ro)

The number of people an infected person infects.

Ro < 1

Does not pose a risk for major infectivity.

Ro > 1

Poses a risk for viral spread.

Measles danger

Highly contagious; can be fatal or cause brain damage; Ro = 13-18.

Effect of mumps

Can cause sterilization of boys, affecting the epididymis.

Rubella outcomes

Less contagious; can cause miscarriage or birth malformations.

Herd immunity vaccination percent

At least 95% of a population must be vaccinated.

Temperate phages

Another name for lysogenic phages.

Temperate phage lytic cycle stages

Adsorption and penetration stages occur.

Prophage definition

A phage genome inserted into a specific bacterial chromosome site.

Integrase function

Enzyme responsible for integrating viral DNA into host cell DNA.

Lysogenic virus genome crossover requirement

Requires a complementary DNA sequence to integrate.

Induction process

Activation of a prophage to enter the lytic cycle.

Induction causes

Occur due to UV light, chemicals, or environmental cues.