Chapter 6 - Intro to Viruses - (NSU - BIOL 251) - Microbiology by Talaro

All viruses have capsids which are ____________________________________.

protein coats that enclose & protect their nucleic acid.

each capsid is made of identical subunits called ______________ made of ______________.

capsomers

proteins

What are the two shapes of capsids?

-helical

-iscosahedral

What is the specialized capsid only with bacteriophages?

complex

What are the 6 steps in virus replication? describe them.

adsorption - binding of virus to receptor

penetration -genome enters host cell

replication - viral components produced

assembly - viral components assembled

maturation - completion of viral formation

release - viruses leave cell to infect other cells

Lysogeny

bacterial chromosome carries phage DNA

What must a cell have for a virus to infect it? (2)

have a specific receptor on its surface for viral attachment

has to contain all of the enzymes and materials needed to produce new virions

What are the three Differences between phage and animal virus replication?

Animal virus replication is more complex than phage replication because host cells are more complex.

Animal viruses cannot inject their DNA.

Lysogeny for phage, latency for animal viruses

What are the two way viruses penetrate?

- via a vesicle (endocytosis)

-goes through membrane (only enveloped)

RNA viruses compared to DNA are _________

unstable and senstitive

What are the seven Cytopathic effects- virus-induced damage to cells?

1. changes in ______________.

2. Cytoplasmic ______ _________.

3. Nuclear _________ ________.

4. Cells that form ___________.

5. Cell ____________.

6. alter __________.

7. ________________ genes.

1. changes in size & shape

2. cytoplasmic inclusion bodies

3. nuclear inclusion bodies.

4. cells fuse to form multinucleated cells

5. cell lysis

6. alter DNA

7. oncogenic genes

how do we grow viruses?

via the required appropriate cells to replicate

What are the 3 media used to grow viruses?

live animals tissues

bird embryos

cell culture (human cells and culture)

What are prions? what do they cause?

misfolded proteins, contain no nucleic acid

encephalopathies - holes in the brain

what is the size range of viruses?

0.02-0.3 nanometres

What do viruses possess that allows adhesion to cells?

glycoprotien spikes

What are the two cycles viruses can go through (both animal and phage)

Lytic and Lysogenic (dont mix up with lysogeny vc latent)

Describe the lytic cycle

- the viral genome directs the cell to manufacture new capsid proteins and replicate the viral genome

- new viruses are assembled inside the cell

-the new viruses either bud from the cell surface or erupt en masse from the cell, killing the host cell

Describe the Lysogenic Cycle

- viral genome is inserted into host genome (prophage/ provirus)

--the viral genome remains in a latent state or lysogeny without causing disease

-- each time the cell replicates, the viral genome is copied

- stressor = viral genome is activated and proceeds to direct the production of new viruses entering the lytic cycle

What is the immune response to viruses?

initially by monocytes and lymphocytes and inflammation site of viral entry - antibody production follows

A fully formed extracellular particle that is virulent is a?

virion

Some animal viruses remain ________ and bacteriopahges remain ________ where they do not enter the lytic stage and lyse cells?

latent

lysogenic

When growing viruses on tissue you detect them when you see ___________.

plaques

Why are viral infections hard to treat?

the drugs that attack viral replication also have serious side effects in host

Viruses

Small (usually <0.2 um) noncellular particles with a definite size, shape and chemical composition

Ecological niche for viruses

Obligate intracellular parasites

Capsid

the protein shell enclosing the viral genome; may be rod-shaped, polyhedral, or more complex in shape; made from protein subunits (capsomeres)

Nucleocapsid

Capsid together with the nucleic acid in a virus

Viral Envelope

a membrane, derived from membranes of the host cell, that cloaks the capsid; vesicles can leave (exocytosis)

naked viruses

Viruses lacking an envelope

Helical

Continuous helix, of capsomers forming a cylindrical nucelocapsid

Icosahedral

20-sided with 12 corners

are spikes considered a virulence factor?

Yes

Complex viruses: atypical viruses

Poxviruses and bacteriophages

Lipoproteins

Proteins attached to fats/lipid molecule

Viral genome

Either DNA or RNA, never both; carries necessary genes needed to invade host cells and redirect cell's activity to make new viruses

Obligate parasite

is a parasitic organism that is completely dependent on its host for survival and reproduction

Central core of a virus

Nucleic Acid molecules; (DNA OR RNA) and Matrix Proteins enzymes ( not found in all viruses)

Covering of a virus

-capsid

-envelope (not found in all viruses)

nucleocapsid

capsid and nucleic acid together

envelopes are made of...

phospholipid bilayer

naked virus

virus without an envelope

Functions of Capsid/Envelope

Protects the nucleic acid when the virus is outside of the host cell

Helps the virus bind to a cell surface and assists the penetration of the viral DNA or RNA into a suitable host cell

Complex Viruses

a typical viruses such as poxviruses and bacteriophages

lipoproteins

proteins attached to fats/lipid molecule

viral genome

either DNA or RNA but never both

DNA viruses

Usually double stranded (ds) but may be single stranded (ss)

Circular or linear

RNA viruses

Usually single stranded, may be double stranded, may be segmented into separate RNA pieces

ssRNA genomes

-range from 2300 to 31,000 bases

-generally have fewer genes

-more fragile than double stranded nucleic acids

positive sense RNA

Single-stranded RNA genomes ready for immediate translation into proteins

negative sense RNA

RNA genomes that need to be converted into the proper form to be made into proteins

replicase

copy RNA

polymerase

an enzyme that brings about the formation of a particular polymer, especially DNA or RNA.

reverse transcriptase

An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.

host range

the spectrum of host cells a virus can infect

budding

exocytosis; nucleocapsid binds to membrane which pinches off and sheds the viruses gradually; cell is not immediately destroyed

lysis

nonenveloped and complex viruses released when cell dies and ruptures

scrapie

prion disease in sheep

BSE (Bovine Spongiform Encephalopathy)

prion disease in cattle; mad cow disease

wasting disease

prion disease in elk

Creutzfeldt-Jakob Disease (CJD)

progressive, incurable, neurologic disease caused by infectious prions

Transmission of HIV

Sexual contact, shared needles, contact with blood, mother to baby

Treatment for HIV

1. Antiretroviral therapy:

Can increase the length of time between a person getting infected with HIV and developing symptoms of AIDS, significantly helping to prolong life.

2. Check T-lymphocyte cell count

HIV targets and destroys

Helper T cells

3 stages of HIV

acute, chronic, AIDS

influenza

(flu) is a viral respiratory illness that results from infection of the nose, throat, and occasionally lungs

transmission of flu

aerosol droplets

at risk population of flu

everyone

post-acute sequelae of SARS-CoV-2 infection

"Long COVID": ongoing, relapsing, or new symptoms or conditions present 30 or more days after COVID infection

transmission of SARS-CoV-2

respiratory droplets