Chapter 13 Viruses and Prion

virion

a virus particle

nucleocapsid

capsid and nucleic acid together

capsid

Outer protein coat of a virus

capsomere

subunit of the capsid

temperate bacteriophage

bacteriophages which can choose between a lytic and lysogenic pathway of development

prophage

A phage genome that has been inserted into a specific site on the bacterial chromosome.

lysogen

a bacterium containing a prophage

lysogeny

a state in which phage DNA is incorporated into the host cell without lysis

provirus

viral DNA that inserts into a host genome

oncogene

cancer-causing genes that are formed due to mutations

What are the components of a naked virus?

capsid, nucleocapsid

What is the composition of a capsid?

protein coat composed of subunits called capsomeres

What are the three general types of capsids?

isometric, helical, complex

How are enveloped viruses different from naked viruses?

enveloped viruses surrounded by lipid bilayer

What is the composition of the chromosomes of viruses?

either DNA or RNA, single or double stranded, circular or linear (RNA only linear)

What are the general characteristics of viral replication?

host/tissue specific, specificity due to virus ligand/host cell receptor binding event, cannot replicate outside host cell

What is responsible for the host/tissue specificity of viruses?

tropisms

Why can't viruses replicate outside of a host cell?

utilize host cell enzymes ribosomes nucleotides proteins, replication is multi-step

What are the possible outcomes of virus/host cell interactions?

production of infection (host dies or multiplies) or latent state

List the steps that occur in bacteriophage lytic replication

attachment, genome, synthesis, assembly (maturation), release

Attachment bacteriophage lytic replication

mediated by tail fibers to specific receptor on host

Genome entry bacteriophage lytic replication

injection of DNA through wall and membrane to cytoplasm

Synthesis bacteriophage lytic replication

early viral mRNA/proteins produced, DNA replication, late protein synthesis

Assembly (maturation) bacteriophage lytic replication

formation of active virion/bacteriophage from elements

Release bacteriophage lytic replication

release bacteriophage, mediated by lysozyme, host cell lysed

What events occur during lysogeny?

attachment, injected linear DNA, prophage is integrated into bacterial chromosome, cell division, excision of phage DNA, replication of phage DNA, cells lyse, releasing new phage

What is the difference between lysogeny and lytic replication?

lytic = immediate, rapid replication and the destruction of the host cell, lysogeny = viral DNA integrating into the host's DNA to replicate along with it without immediate destruction

What causes lysogeny to end?

ends when bacterial cell is going to die

What happens when lysogeny ends?

jumps back into lytic replication to make more phage and release before host cell dies

What is meant by lysogenic conversion?

lysogenic bacteriophage can carry genes that encode toxins (which cause disease)

What are examples of diseases caused by bacteria that have undergone lysogenic conversion?

streptococcus pyogenes (scarlet fever), clostridium botulinum (botulism), corynebacterium diphtheriae (diphtheria)

What is the difference between generalized transduction and specialized transduction?

specialized only contains DNA next to wear prophage is located

Generalized transduction

a piece of host cell DNA is packaged instead of viral nucleic acid

Specialized transduction

only during lysogenic infections, prophage takes some bacterial DNA when leaving chromosome, packaged into virions

How are animal viruses classified?

genome structure, virus particle structure, presence or absence of an envelope

Be able to distinguish between family names and genus names.

family ends in viridae, genus ends in virus

How are family names derived?

genome, virus structure, envelope

How are species names derived?

disease it causes (poliovirus, ebola virus, influenza virus)

Be able to list steps in animal virus replication.

same 5 basic steps as virus, attachment, penetration and uncoating, targeting site of replication, synthesis, assembly

Attachment animal virus replication

glycoproteins on cell membrane, function of glycoproteins to host cell

Targeting to site of replication animal virus replication

DNA -> nucleus, RNA -> viruses

Release from host cell animal virus replication

budding, exocytosis, lysis

What are the ways in which enveloped animal viruses can enter host cells?

fusion or endocytosis

What are the ways in which naked animal viruses enter host cells?

endocytosis

Be able to list and describe the steps involved in fusion

attachment through spikes, membrane fusion, nucleocapsid released into cytoplasm, uncoating nucleic acid separated from capsid

Be able to list and describe the steps involved in endocytosis.

attachment to receptors, endocytosis form endocytic vesicle, release from vesicle, uncoating

What is meant by the shedding of viruses?

means of exit from host cell, usually through same surface as entry

How is shedding different from transmission?

shedding is the means of exit from host

transmission is the means of entry into a new host (droplets, direct contact, sexually)

What are the characteristics of acute animal virus infections?

short in duration, infection cells dies, virus shed during infection, infected host develops immunity

What are the essential steps of an acute infection?

prodromal stage, disease stage, convalescent stage

Prodromal stage

infected and replicating, can transfer to others but have no symptoms

Disease stage

symptoms present, immune system responding

Convalescent stage

feel better but still infectious, immune system working

How are persistent viral infections different from acute infection?

virus continually present, may or may not cause disease, people are always carriers

What are the categories of persistent infections

Latent infections, chronic infections

Latent infections

symptoms can be short but virus is still released from host with no symptoms

Chronic infections

initial infection virus is maintained in neurons in non-infectious state can be reactivated to produce symptoms

Be familiar with the examples of HSV as a latent infection.

dormant state in the sacral ganglia (lower spine) for genital herpes, and in the trigeminal ganglia (behind the cheekbone) for oral or facial herpes

What is a tumor (neoplasm)?

swelling caused by abnormal cell growth

What is the difference between a benign and a malignant tumor?

benign remains confined, malignant spreads

What, in general, is the cause of tumors?

non-functional or malfunction of cell growth controls

What are proto-oncogenes

genes that encode proteins

what are the functions of the proteins produced from proto-oncogenes?

regulate cell growth or differentiation

What is meant by viral transformation of cells?

some viruses will cause cells to become tumor cells upon infection

How do viruses transform cells?

retroviruses

What are the characteristics of retroviruses?

RNA viruses that become proviruses when they infect cells

What enzyme allows them to convert their RNA genome into DNA?

reverse transcriptase

How do retroviruses transform cells?

carry oncogenes which creates unregulated cell growth

What determines the host range for a given virus?

defined by virus ligand/host cell receptor

What are prions?

proteinaceous infectious particles

What diseases are associated with prions?

Transmissible spongiform encephalopathies, including mad cow disease and Creutzfeldt-Jakob disease

What are the characteristics of prions?

composed only of proteins, highly resistant to heat and chemicals

How does one acquire a prion?

consumption, handling of contaminated items; some forms can be genetic

How do prions "replicate"?

abnormal protein converts normal protein to abnormal