Microbiology Ch.13 - Characterizing and Classifying Virus, Viroids, Prions

dsDNA virus synthesis

similar to replication of normal cellular DNA and translation or proteins

- replication usually happens in the nucleus

ssDNA virus synthesis

enters a cell and host synthesizes a complementary strand of DNA to viral genome

(animals do not use ssDNA)

+ssRNA virus synthesis

ribosomes of the host cell directly translates proteins using the codons of these types of viruses

- the +ssRNA virus is recognized as a mRNA by the cell

EX: poliovirus

What type of RNA do retroviruses have?

+ssRNA

What enzyme do retroviruses use to create cDNA?

Reverse transcriptase

Do retroviruses use their genome as mRNA?

No

What does the newly made DNA serve as for retroviruses?

A template to make more of the retrovirus

What is an example of a retrovirus?

HIV

What enzyme do -ssRNA viruses carry in their capsids?

RNA dependent RNA transcriptase

Can host ribosomes translate a -RNA strand?

No

What does the transcriptase enzyme create from -ssRNA strands?

+RNA strands

What can +RNA strands serve as for -ssRNA viruses?

mRNA for creating more of the virus's genome and proteins

What can the +RNA strand of a dsRNA virus do?

It can act directly as mRNA.

What can the -RNA strand of a dsRNA virus be transcribed into?

+RNA.

What is the next step after the -RNA strand is transcribed into +RNA?

It can then be translated.

What is an example of a virus that has dsRNA synthesis?

Certain retroviruses.

assembly and release of DNA

assembled in: nucleus

released from: into cytoplasm then outside

assembly and release of RNA

assembled in: cytoplasm

released from: cytoplasm

# of viruses produced depends on what

1. the type of virus

2. health of the host cell

do animal viruses or bacteriophages take longer to replicate

animal viruses

enveloped virus release

Budding process through the plasma membrane.

What is budding in asexual reproduction?

offspring is created from the body of the parent

- parent usually remains alive unless too weak

persistent infection means

a long steady release of virions

Naked viruses released by

exocytosis or lysis

what is exocytosis

Fuses with plasma membrane & releases contents outside of the cell (exo = exit)

what is lysis

the bursting of a cell

latent virus means

some viruses can remain inactive in the host for years before becoming active

EX: PROVIRUSes

what are proviruses

DNA copies of retroviruses inserted into chromosomes

how do latent viruses work

They stay in the cell awhile before activating so they can combine their genetic material with the cell's genetic material

- never becomes part of the host cell's DNA

- if viral DNA is incorporated into the host, it is permanent and will be passed on to all descendants of that cell

role of viruses in cancer

Animal's genes dictate that some cells can no longer divide or are prevented from unlimited division

Genes for cell division "turned off" or genes inhibiting division "turned on"

viruses are thought to cause what % of cancers

20-25%

cervical cancer is often caused by what

HPV (human papilloma virus)

- it affect the mucoid membrane epithelial cells

protooncogenes

genes in a host cell involved in normal cell division

What is the first hit in the two hit hypothesis?

A virus inserts a promoter that converts a protooncogene into an oncogene.

Does the first hit in the two hit hypothesis cause cancer?

No, it does not cause cancer yet.

What is the second hit in the two hit hypothesis?

A virus enters and damages the downstream repressor gene.

What is the result of the second hit in the two hit hypothesis?

The oncogene disrupts cell division and causes cancer.

how do viruses impact how genes behave

they can get incorporated into genome and affect parts like the repressor

what are prions

misfolded versions of normal protein that can cause disease

how do prions work

Protein infects and changes the shape of useful proteins to prevent them from doing their job

how long does it take for prions to show symptoms

can take up to 40-60 years

What happens to the normal PrP protein structure in human prion disease?

It becomes altered.

What effect does the altered PrP protein have on other PrP proteins?

It begins to affect other PrP proteins around it.

What is a consequence of the alteration of PrP proteins in human prion disease?

It causes neurons to die.

What is a result of neuron death in the brain due to prion disease?

It leaves holes in the brain.

diseases caused by prions are called

spongiform encephalopathies

examples of prion diseases

BSE - mad cow disease (can be spread to humans)

CWD - in deer and elk

vCJD - in humans (inherited by family)

how prions can be spread

- ingestion of infected tissue (eating nervous tissue like brain or spinal cord)

- transplants of infected tissue (surgical equipment)

- contact between infected tissues and mucous membranes

prion fatality rate

100% fatal

can prions be removed

can not be removed through normal autoclaving or decontamination processes