Neurovirology Exam 1 L1

Reverse transcriptase does what? It is a ___-dependant ____ polymerase

Goes from RNA to DNA RNA dependent DNA polymerase

Example of a virus with complex structure

Poxvirus, a virus of vertebrates

tegument

area between envelope and nucleocapsid

nucleocapsid

capsid containing nucleic acid genome

icosahedral symmetry

capsomeres form 5:3:2 symmetry icosahedronn has 20 triangular facets

helical symmetry

capsomeres form a spiral staircase or helix. -RNA forms a spiral within the nucleocapsid

True or False? Enveloped viruses can be of either icosahedral or helical symmetry

true. However, not all viruses are enveloped.

List 4 characteristics of envelope

1. Acquired from host cell during maturation process == a process called budding == may be tight-fitting or loose-fitting ==loose-fitting envelopes cause structure variations (pleomorphic) 2. A modified cell membrane == plasma membrane ==inner nuclear membrane ==golgi ==ER 3. lipids of envelope are directly derived from the host cell membrane 4. Glycoproteins of envelope are virus-encoded == fxn in attachment to receptors on cell surface == fxn in immune response (antigenic) ==may stimulate neutralizing antibodies (vaccines) ==forms structures known as peplomers or spikes, which are used to attach to specific cell.

List the 10 steps in virus replication. Each step is a potential antiviral target

1. Attachment ==surface proteins of the virus and specific receptors found on the surface of the host cell ==lock and key mechanism 2. Adsorption (penetration) ==energy dependent mechanism that takes place immediately after attachment, involves changes in the plasma membrane of the host cell 3. Uncoating ==sets stage for expression of virus genome 4. Transcription of early mRNAs 5. Translation of early proteins (enzymes) ==nonstructural proteins ==enzymes for nucleic acid and genome replication 6. Replication of parental virus genome ==copies of new genomes produced to become incorporated into progeny virus particles ==cellular and virion-encoded polymerases ==parental genome is the template 7. Transcription of late mRNAs 8. Translation of late proteins (structural proteins and glycoproteins) 9. Assembly of virions ==structural proteins aggregate and associate with genomes to form nucleocapsids of progeny virus particles (self-assrmbly) ==assrmbly in the nucleus or cytoplasm 10. Release

List characteristics of RNA Genomes

1. Small, with limited coding capacity 2. Mostly SS genomes (exception reovirus) ...R in reovirus ...also generally RNA is SS, do the exception has to be DS 3. single molecule and segmented 4. helical symmetry 4. most RNA viruses assemble in cytoplasm, but exceptions! (orthomyxoviruses)

Gives details on complex structure of virus

1. Virions are brick-shaped ==external coat consists of lipid and tubular/globular protein structure ==coat encloses lateral bodies (organelles?) ==coat encloses internal body (core_ that contains the genome 2. Virions replicate in cytoplasmic factories as seen by light microscopy

Give 3 characteristics of tegument

1. area btw envelope and nucleocapsid 2. composed of virus-encoded proteins 3. tegument proteins play functional roles in addition to being structural proteins of the virion == fxn as antigens to stimulate immune response == may serve to alter host cell fxns at time of infection

List 7 characteristics of a virus

1. contains DNA or RNA 2. not capable of independent growth (parasite) 3. not capable of independent protein synthesis 4. not capable of independent metabolism 5. replicates by assembly 6. susceptible to antivirals 7. viable even after freezing or crystallization

Enveloped vs. nonenveloped viruses

1. enveloped virus loses infectivity if envelope is removed or disrupted 2. enveloped virus is less stable than a nonenveloped virus (hence, it loses its infectivity if the envelope is removed or disrupted) (they are thermally labile, fall apart faster in hotter temps) (soap also disrupts the envelope of viruses) 3. There are different mechanisms by which enveloped and nonenveloped viruses gain entrance to host cell

symmetries of capsomere

1. icosahedral 2. helical

List characteristics of viruses with DNA genome

1. large or small 2. mostly DS genomes (except parvovirus) 3. circular and linear (think of plasmids, its circular) 4. icosahedral or complex 5. Most DNA-containing viruses assemble in the nucleus but there are exceptions (poxvirus! recall it has complex structure! )

Lit the 5 virus-host cell interactions

1. productive infection ==high production of new infectious progeny virus ==host cell is eventually killed within hours to days 2. chronic pesistent infection ==low level of new infectious progeny production ==host cell survives for long period of time ==host cell fxns are either not affected or partially impaired 3. abortive infection ==replication blocked at any step after attachment/adsorption ==host cell cant supply some virus requirement, so productive infectin is terminated ==host cell sustains neglibible consequence (injury) or extensive (death) 4. latent infection ==virus becomes quiescent ==virus genome is conserved but little transcription/translation ==future events may trigger reactivation of productive virus replication 5. transformation ==results in heritable change in host cell ==interaction doesnt kill host cell but changes its phenotype, endowing the host with new properties ==change in phenotype results in more vigorous growth, immportalization in vitro and malignancy in vivo ==cancer-causing viruses

How many classes are there in the Baltimore Classification Scheme?

6

How are animal viruses classified? Hint: 4 ways!

==nucleic acid and structure of genome 1. DNA or RNA genome 2. Single stranded (SS) vs. double-stranded (DS) 3. linear or circular genome 4. single molecule vs. segmented genome

Reverse transcriptase does what? It is a ___-dependant ____ polymerase

Goes from RNA --> DNA, so its an RNA-dependant DNA polymerase

List the Baltimore classification scheme with details

Class I: DS DNA --> RNA DNA dependent RNA-polymerase Class II: SS DNA ---> DS DNA --> RNA DNA dependent RNA-polymerase Class III: DS RNA --.> RNA virion-associated RNA dependent RNA polymerase Class IV: THIS ONE IS EASY! RNA already of + polarity so it can immediately go to the ribosome to be transcribed Class V: ------------- SS RNA (-) must be transscribed into mRNA via a virion-associated RNA-dependent RNA polymerase Class VI:--------------------- SSRNA --> SS DNA via virion-associated reverse transcriptase then converted to DS DNA this DS DNA is integrated into the cellular genome (provirus) and subsequently transcribed into mRNA

what is a positive (+) strand mRNA?

It contains immediately translatable info

What are RNA and DNA complements of (+) strands called?

Negative strands

What's the purpose of spikes/peplomers?

Spikes (peplomers) are found in enveloped viruses, they help the virus recognize and attach to a cell

capsid

protein coat

virion

infectious virus particle

Virus

intracellular parasite that must use the host cell's machinery to make new progeny infectious virus particles

envelope

lipoprotein membrane surrounding the capsid. its basically an additional structure that surrounds the nucleocapsid.

This biological molecule is central to the programming of virus protein synthesis

mRNA

capsomere

morphological subunit of capsid

Positive or negative RNA genome functions as mRNA

positive!