Biomed Exam #2

What is a Virus?

An infectious, obligate intracellular parasite comprising genetic material (DNA or RNA) surrounded by a protein coat and/or a membrane

Can the genetic material in the virions be both DNA or RNA?

no

The two phases viruses exist in

- Metabolically inert

- Infected cell

What can viruses not make?

Their own energy and their own proteins

What do all viruses need to make that can be translated by host ribosomes?

mRNA

Bacteriophage virus replication cycle

1. Attachment

2. Genome Entry

3. Synthesis

4. Assembly

5. Release

Viruses can replicate, producing more virus progeny, outside of a host cell. Viruses multiply by binary fission.

A. Both statements are TRUE

B. Both statements are False

C. The first statement is TRUE, the second statement is FALSE.

D. The first statement is FALSE, the second statement is TRUE

B. Both statements are FALSE

Which of the following is TRUE concerning bacterial vs. viral replication?

A. Viruses must assemble using pre-formed components

B. Bacteria do not replicate via binary fission as viruses do

C. Bacteria must assemble using pre-formed components

D. Viruses replicate by binary fission

E. All of the answers are TRUE

A. Viruses must assemble using pre-formed components

What does the Family of viruses always end in?

-viridae

What does the genus of viruses always end in?

-virus

the 4 things that classify viruses

1. Host

2. Genomic Nucleic Acid

3. Outer Surface Coating

4. Type of Capsid

Types of DNA Viruses

- dsDNA (e.g. Herpesviruses, Poxviruses)

- ssDNA (e.g. Parvoviruses)

- Partially dsDNA (e.g. Hepadnaviruses)

Types of RNA Viruses

- dsRNA (e.g. Reoviruses)

- ssRNA (+) (e.g. Coronaviruses)

- ssRNA (-) (e.g. Orthomyxoviruses)

- ssRNA (+) via DNA (e.g.) Retroviruses

What is the Virion

Entire virus particle

What does it mean when a virus is segmented

It has more than one RNA

What is the Genome

DNA or RNA, single or double-stranded

What is the Viral Capsid

Protein shell, composed of repeated units called capsomeres

What shape can a Capsid be

icosahedral or helical

What is the Nucleocapsid

Capsid + Genome

What is the Envelope

Lipid coating on outside, derived from host plasma membrane

What does the surface (Envelope or Capsid) contain

glycoprotein spikes

Double stranded DNA (Non-enveloped) viruses

- Papillomaviridae

- Polyomaviridae

- Adenoviridae

Double stranded DNA (Enveloped) viruses

- Herpesviridae

- Poxviridae

Single stranded DNA (Non-enveloped) viruses

- Parvoviridae

Double stranded RNA (Non-enveloped) viruses

- Reoviridae

Single-stranded RNA (Non-enveloped) viruses

- Picornaviridae

- Caliciviridae

Single-stranded RNA (plus) Enveloped viruses

- Togaviridae

- Flaviviridae

- Coronaviridae

Single-stranded (minus strand) Enveloped viruses

- Rhabdoviridae

- Filoviridae

- Paramyxoviridae

- Orthomyxoviridae

- Bunyaviridae

- Arenaviridae

All of the following statements are true regarding viruses, EXCEPT for one. Which is the EXCEPTION?

A. All viruses must be infectious to endure in nature

B. Some viral infections are asymptomatic

C. All viruses are covered by a lipid membrane

D. Viruses must be able to self-assemble

E. There is no exception, all of the answers are actually true

C. All viruses are covered by a lipid membrane

How may an Enveloped Virus penetrate a cell?

Membrane fusion

How may an enveloped virus be released from a cell?

by budding (non-lytic)

How may a Non-enveloped Virus be released from a cell?

by lysis (cell popping)

Tropism?

Target cells that a virus is able to infect (cell has receptors for attachment

Tropism for specific species

humans vs all mammals (Papillomaviruses are highly species specific)

Tropism for specific tissues

epithelia cells vs neurons vs white blood cells (HSV replicates in neurons and epithelium)

If a cell can support virus replication it is _____

Permissive

What does a permissive cell have?

- Proper surface receptors for the virus (Attachment)

- Biosynthetic machinery to support the complete replicative cycle of the virus (Transcriptional factors, Posttranslational processing enzymes, etc.)

A _______ cell may support some but not all viral replication steps leading to inefficient replication

Semipermissive

________ cells do not allow the replication of a particular strain of virus

Nonpermissive

What do Nonpermissive cells lack

a receptor, necessary enzyme pathway or transcriptional activator

What do Nonpermissive cells express

an antiviral mechanism that inhibits replication

What are the 6 basic steps of viral replication

1. Attachment

2. Penetration and Uncoating

3. Synthesis of viral proteins and replication of the genome (mRNA production, translation, genome replication)

4. Assembly

5. Release

6. Repeat

What does replication require?

a permissive cell (receptor for viral attachment, appropriate machinery for replication of virus and release of virus)

Attachment (Adsorption)

binding of virion to host cells, usually glycoproteins on the cell membrane (permissive cells)

Penetration

mechanism by which virus gains access to interior of the cell

Uncoating

release of the genome from the capsid

Transcription

viral genes (DNA or RNA) to mRNA

Translation

mRNA to protein

Replication

production of progeny copies of the virion nucleic acid (RNA or DNA)

Assembly

production of new virions from the newly synthesized components

Release

process by which new virions leave the cell

What is Viral Attachment protein?

Protein or glycoprotein that attaches to cellular receptors

- Target of neutralizing antibodies

SARS-CoV-2 attachment protein and cellular receptor

- Attachment protein: Spike

- Cellular receptor: Angiotensin converting enzyme II (ACE2)

Budding

- capsid and proteins push out of cell membrane taking lipid bilayer with them (enveloped virus)

Cell lysis

- non-enveloped virus, or enveloped (got a membrane from an organelle)

Exocytosis

- virus inside the cell has membrane that fuses with the lipid bilayer and gets released (non-enveloped, enveloped - has two membranes before exocytosis)

The process of producing mRNA from a DNA template is called?

Transcription

The process of producing protein from RNA is called?

Translation

What is translation performed by?

ribosomes of the cell (never viral)

What are the three things that need to happen during every successful viral infection

1. Viral mRNA must be made, regardless of the type of viral genomic nucleic acid

2. Virus must use cellular components and energy to synthesize proteins from mRNA (proteins for structure, polymerases, enzymes, evasion proteins

3. Must replicate its genomic nucleic acid to package in the new virions

+ sense (coding strand) RNA

genome functions as mRNA, proteins made immediately

- sense (non-coding strand) RNA

must made complementary + sense RNA first

Translation

ribosomes read mRNA (+ sense) to make protein

Why does viral replication always require RNA-dependent RNA polymerase

Polymerase lacks proofreading activity - make more mistakes

DNA polymerase

- Make DNA from DNA template

- Often provided by host cell (cellular DNA replication)

- Some viruses encode their own (Parvo, Pox, Herpes)

DNA-dependent RNA Polymerase

- Make RNA from DNA template

- Host cell: RNA Polymerase II (from mRNAs)

- Poxvirus RNA Polymerase (extra-nuclear life cycle)

RNA-dependent RNA Polymerase

- Make RNA from RNA template

- NOT a cellular function (ever)

- Must be encoded by virus

RNA-dependent DNA polymerase

- Made DNA from RNA template

- NOT a cellular function (ever)

- Reverse transcriptase (HIV, HBV, cellular telomerase)

- Must be encoded by virus

DNA → DNA

DNA dependent DNA polymerase

DNA → RNA

DNA dependent RNA polymerase

RNA → RNA

RNA dependent RNA polymerase

RNA → DNA

RNA dependent DNA polymerase

DNA virus

- DNA in their virion

- May contain ssDNA, dsDNA, or partial dsDNA

- Many establish persistent infections (latent, chronic, etc.)

- Genome may be linear or circular

Where does the replication of DNA viruses occur?

in the nucleus

What is the first step of a ssRNA (-) virus in making an mRNA that can be translated?

A. Must first be copied into (+) sense RNA by a cellular RNA-dependent RNA polymerase

B. Must first be copied into (+) sense RNA by a viral DNA-dependent RNA polymerase

C. Must first be copied into (+) sense RNA by a viral RNA-dependent RNA polymerase

D. The (-) sense genome can be immediately translated, it can act as the mRNA

C. Must first be copied into (+) sense RNA by a viral RNA-dependent RNA polymerase

Retrovirus

- RNA genome - ssRNA (+) genome

- Virion contains reverse-transcriptase

- RNA goes in, make DNA, make new RNA

Replication of reverse-transcribing viruses

- Encode reverse transcriptase: makes DNA from RNA

- Retroviruses have ssRNA (+) genome (e.g., HIV)

- Reverse transcriptase synthesizes single DNA strand

- Complementary strand synthesized; dsDNA integrated into host cell chromosome

- Can direct productive infection or remain latent

- Cannot be eliminated

What is a property of a ssRNA (+), non-enveloped virus? (e.g. poliovirus)

A. Replicates nucleic acid in nucleus

B. Resistant to dry environment

C. Sensitive to acidic pH

D. Uses cellular RNA polymerase for replication

B. Resistant to dry environment

Which type of virus must bring along a synthesized, pre-made RNA-dependent RNA polymerase in order to successfully infect a cell and eventually get new viral proteins made?

A. dsDNA virus

B. (+) ssRNA virus

C. (-) ssRNA virus

C. (-) ssRNA virus

What is nucleic acid of the eukaryotic genome?

dsDNA

The process of protein synthesis is called translation (T/F)

True

Which virus has an outermost layer consisting primarily of protein and is more resistant to harsh conditions?

Non-enveloped viruses

Which of the following is True regarding viruses?

a. all viruses can make us sick and can be lethal

b. human viruses can be seen using a light microscope

c. some viruses can have RNA genomes

d. humans are usually infected with one virus at a time

c. some viruses can have RNA genomes

(Select all that apply) which of the following are components of viruses?

a. Ribosomes

b. Mitochondria

c. Peptidoglycan

d. None of the answers are components of a virus

The process of going from rna to protein is called transcription (T/F)

False

Which type of virus is most likely to remain infectious after passing through the low pH of stomach

Non-enveloped

Which type of virus can be spread more easily by fomites?

Non-enveloped Virus

Which type of virus can have DNA as its nucleic acid?

Both Enveloped and Non-enveloped

Which type of virus has a outermost layer consisting of primarily protein?

Non-enveloped Virus

Which type of virus has glycoprotein spikes used for attachment?

Both Enveloped and Non-enveloped

Which type of virus can be released from a cell by budding?

Enveloped virus

Which type of virus must stay wet to survive because it cannot tolerate drying/dessication?

Enveloped Virus

Which type of virus has an outermost layer consisting of primarily lipids?

Enveloped virus

Which type of virus can be neutralized by antibody binding to viral attachment proteins?

Both Enveloped and Non-enveloped

The first step in the viral replication cycle is Attachment (T/F)?

True

A cell that a virus can successfully infect and replicate within is called a ______ cell

Permissive

What is the general name for a cellular component to which a viral attachment protein binds to?

Receptor

Which of the following occurs first in the viral replication cycle?

a. penetration/entry

b. budding

c. assembly

d. uncoating

a. penetration/entry

Antibodies that block attachment of a virus to a host cell are called opsonizing antibodies (T/F)

False