Microbiology Viral Structure & Multiplication

plaques

areas where virus-infected cells have been destroyed and show up as a clear, well-defined patches in the cell sheet

Prominent viral infections worldwide:

COVID19

Bacteriophage

"bacteria eating" -most contain double-stranded DNA, but some RNA types as well -every bacterial species is parasitized by various specific bacteriophages

In vivo

"in-life" laboratory-bred animals and embryonic bird tissues

Types of CPEs include

- Gross changes in shape and size - Development of intracellular changes - Inclusion bodies - Syncytia

regular lytic cycle steps

1.Adsoption: bacteriophage binds to the bacterial cell 2. Penetration: injects its nucleic acid. 3. Duplication: then nucleic acid is free within that cell, replicates its virus genetic material 4. Biosynthesis: assembly of new virions 5. Maturation 6. Lysis of weakened cell and release of viruses

Seawater can contain ___________ viruses per milliliter.

10 million

poliovirus-infected cell has ___________ virons

100,000

poxvirus-infected cell has ___________ virons

3,000 t0 4,000

herpesviruses completes replication cycle in

36 hours (longer)

poliovirus completes replication cycle in

8 hours (Fast)

Retroviruses turn their RNA genomes into

DNA

DNA viruses replication in human cells

DNA virus uses the DNA dependent DNA polymerase in host cells to replicate themselves. Process called transcription. Then virus uses the DNA dependent RNA polymerase to transcribe those genes. Then you get translation which gets you viral proteins.

Nucleic acid can be either ______ or _______, but not both.

DNA; RNA

Viruses are better described as ______ or _____ rather than alive or dead

active; inactive

DNA polymerase is

an enzyme that makes DNA. Going to make DNA molecules

RNA polymerase is

an enzyme that makes RNA. Going to make RNA molecules

DNA dependent DNA polymerase

an enzyme that uses DNA as the template for producing DNA (your cells use this to replicate)

what is polymerase?

an enzyme which brings about the formation of a particular polymer, especially DNA or RNA. Word in front of polymerase is what is going to be made

RNA viruses:

can be double-stranded, but more often are single-stranded

envelope

external covering of a capsid, usually a modified piece of the host's cell membrane

Viruses contain DNA or RNA, but ______ _______.

not both

Cells that lack compatible virus receptors (lock) are resistant to invasion of virus spikes (key). true/false

true

Cells that lack compatible virus receptors are resistant to adsorption and invasion by that virus. true/false

true

Easier to develop vaccines to prevent viral diseases. true/false

true

Even though viruses do not exhibit most of the life processes of cells, they can direct them, and thus are alive. true/false

true

Viruses have a specific host range. true/false

true

Viruses infect every type of cell. true/false

true

Host range is limited by

type of host cell receptors on cell membrane

RNA dependent DNA polymerase

uses RNA to make DNA (reverse transcriptase)

phases of the animal virus replication cycle:

Adsorption Penetration Uncoating Synthesis Assembly Release

Segmented RNA viruse

individual genes exist on separate pieces of RNA, transitional jumps have to occur

Properties of Viruses

-Hostile takeover of host cells to replicate -Lack enzymes for most metabolic processes -Lack machinery for synthesizing proteins

Primary purposes of viral cultivation:

-Isolate and identify viruses in clinical specimens. -Prepare viruses for vaccines. -Do detailed research on viral structure, multiplication cycles, genetics, and effects on host cells.

Adeno-associated virus (AAV)

-Originally thought that it could only infect cells infected with the adenovirus -Now found to infect cells infected with other viruses

Basic structure of a virus consists of

-external coating (capsid proteins) -core containing one or more nucleic acid strains of DNA or RNA -sometimes one or two enzymes

Delta agent

-naked circle of RNA -expressed only in the presence of the hepatitis B virus -worsens the severity of liver damage

Viruses possess these characteristics

-ubiquitous -size range of 20 nm to 1,000 nm -not made of cells

Reverse transcriptase

-utilizes RNA to make DNA -enzyme that is restricted to the retroviruses because human cells do not ever convert RNA into copies of DNA

DNA viruses synthesis

1. Enter the host cell's nucleus and then takes over host cell's machinery. Uses this machinery to replicate it, and produce new viral proteins

T-even bacteriophage

Infect Escherichia coli (E.coli) icosahedral capsid head containing DNA central tube surrounded by a sheath collar base plate tail pins fibers

How were viruses discovered?

Louis Pasteur hypothesized that rabies was caused by a "living thing" smaller than bacteria

Infections with high mortality rates:

Rabies, AIDS, Ebola

RNA dependent RNA polymerase

Replicases that copy RNA. Humans don't make RNA in its nucleus, so any virus that needs it will have to have an enzyme that produces it for it

HIV only infects

T cells of humans

Lysogenic state in bacteria

The viral DNA molecule is inserted at specific sites on the bacterial chromosome. The viral DNA is duplicated along with the regular genome and can provide adaptive genes for the host bacterium. Doesnt always happen

Virion

a fully formed virus that is able to establish an infection in a host cell

Viruses that infect bacteria are called

bacteriophages

Spikes are found on

both naked and enveloped viruses

Synthesis

replication and protein production

obligate intracellular parasites

cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses bacteria cannot live outside the host cell.

Retroviruses

carry their own enzymes to create DNA out of their RNA ( i.e.HIV)

Enveloped viruses can bud from:

cell membrane, nuclear envelope, endoplasmic reticulum

In vitro

cell or tissue culture methods

Common causes of acute infections:

colds, hepatitis, chickenpox, influenza, herpes, warts

inclusion bodies

compacted masses of viruses or damaged cell organelles in the nucleus and cytoplasm

satellite viruses

dependent on other viruses for replication

The nucleic acid in a virus can be

dsDNA, ssDNA, dsRNA, ssRNA

Once a retrovirus has become positive sense with reverse transcriptase, what does it do?

enters the nucleus of a host cell to be treated as a DNA virus

Penetration through endocytosis

entire virus is engulfed by the cell and enclosed in a vacuole or vesicle

Direct fusion of the viral envelope with the host cell membrane:

envelope merges directly with the cell membrane, liberating the nucleocapsid into the cell's interior

Number of genes in hepatitis B virus?

four genes

syncytia

fusion of multiple host cells into single large cells containing multiple nuclei

If RNA virus is negative sense then it must

have own enzyme that converts it to positive before translation can occur

Hundreds of genes in some ____________

herpesviruses

Almost all antiviral drugs license so far have been designed to target one of the steps in the viral life cycle:

integrase inhibitor class of HIV drugs interrupts the ability of HIV genetic information to incorporate into the host cell DNA

host range

limited range of cells that a virus can infect

SARS-CoV-2 can infect

multiple cells in humans and some animals

-negative sense RNA

must be converted before translation can occur

Naked viruses consist only of a __________________

nucleocapsid

Viruses are

obligate intracellular parasites

Detection of Viral Growth in Culture

observation of degeneration and lysis of infected cells

pleomorphic

organisms that are variable in shape

Visible manifestation of cytopathic effects (CPEs)

plaques

Enveloped viruses are more flexible than the capsid so enveloped viruses are __________

pleomorphic

Pasteur proposed the term virus, which is Latin for __________

poison

Infections that cause long-term disability

polio, neonatal rubella

capsid

protein shell that surrounds the nucleic acid

The number of viral genes is

quite small compared with that of a cell

+Positive-sense RNA

ready for immediate translation

RNA viruses synthesis

replicated and assembled in the cytoplasm

retroviruses always come packed with a

reverse transcriptase

the number of viruses released by infected cells is variable, controlled by:

size of the virus health of the host cell

What allows viruses to dock with host cells (like SARS-CoV-2)

spikes

enveloped viruses

take a bit of the cell membrane when they are released from a host cell

nucleocapsid

the capsid together with the nucleic acid

Release of animal virus

the number of viruses released by infected cells

Viral Tropism

the spectrum of cells of a host that a virus may infect

genome

the sum total of the genetic information carried by an organism

An infectious viral particle is called a

virion

Assembly of animal viruses

virus is put together using "parts" manufactured during the synthesis process

cytopathic effect (CPEs)

virus-induced damage to the cell that alters its microscopic appearance

Words in front of dependent are

what that enzyme uses as a template