Viruses and Prions

A viral particle (a virus) is nucleic acid (DNA or RNA) contained within…

a protective protein coat called the capsid

What are viral particles incapable of?

metabolism, replication, or motility, but their genome can enter a host cell and hijack the cell’s replication machinery, inducing the cell to produce more viral particles

Viruses are ____ intracellular ______

obligate, parasites

Viruses that infect bacteria are called _________ or simply ______

bacteriophages, phages

Phage therapy

use of phages for killing pathogens, including E. coli 0157:H7

Viruses can be a _____ times smaller than the cells they infect and can only be see with an ______ _______

thousand, electron microscope

Names of virus families end in the suffix

-viridae

SARS-CoV-2 is in the family

Coronavirus

Herpes Simplex Virus (HSV-1) causes…. and is in the family…..

oral herpes, fever blister, cold sores, orthoherpesviridae

Enteric (intestinal) viruses

transmitted via fecal-oral route

Respiratory viruses

transmitted via respiratory route

Zoonotic viruses

transmitted from an animal to a human via an animal, called a vector (there’s often a host)

Arboviruses

insect (arthropod) borne. e.g., mosquitoe & ticks - type of zoonotic virus

Bacteriophages causing a ______ infection produce new particles (visions) and the bacterial cell dies

lytic (happens now)

Lytic infection steps

1. Attachment

2. Genome Entry

3. Synthesis of Phage Proteins

4. Synthesis of Phage Genome

5. Assembly

6. Release

lytic infection: attachment

phage collide with host cells by chance and then attach to a receptor on the host cell surface

lytic infection: genome entry

the phage degrades part of the bacterial peptidoglyan cell wall with lysozyme and then injects its genome into the cell

lytic infection: synthesis of Phage Proteins

within minutes, genes on the viral genome are transcribed and translated by the infected cell’s own machinery (bacterial RNA polymerase and ribosomes)

lytic infection syntesis of phage proteins (early vs. late)

Early a nuclease that degrades the host cell’s DNA is produced

Later, new capsids are produced

lytic infection: synthesis of Phage Genome

by bacterial DNA polymerase

lytic infection: Assembly

Phage genome and structural proteins assemble to produce new phage virions

lytic infection: Release

Late in infetion, the phage-encoded lysozyme digests the host cell from within causing the cell to lyse, thereby releasing the phage

The viral genome is incorporated into the host cell’s DNA and remains…

SILENT within the cell, causing no damage. The infected bacterial cell is called a lysogen

Lysogenic conversion

change in the PHENOTYPE of a lysogen because of the virus it carries (e.g., only strains of Coryne bacterium diptheriare that are lysogenic with a certain phage synthesize the tocin that causes diptheria)

The viral DNA is replciated along the host cell’s genome and…

passed to progeny (ex. of vertical gene transfer)

Lysogenic/Latent infection: Later, the inserted virus can remove itself from the bacterial DNA and…

switch to the lytic infection

Transduction is where viruses occasionally

accidentally package bactreial DNA instead of viral DNA and is carried to new bacterial cell when the virion attaches

Animal viruses have attachment proteins (spikes) on their surfaces which bind only to…

specific host cell receptors, so they usually only infect a single cell in one species (rabies are an exception)

With animal viruses, the entire virion enters…

the cell (unlike with phages where only DNA enters)

Many animal viruses make a polyprotein that is later cleaved by…

viral proteases into individual proteins (HIV protease is an important drug target)

Some viruses have an outer _____ ______ they acquire from the host cell as they exist

lipid bilayer (e.g., SARS-CoV-2)

These _________ ______ are more susceptible to….

enveloped viruses, soaps detegrents and disinfectants because damaging the envelope makes them non-infectious

RNA virus replication requires a virally encoded RNA polymerase called a ______ which uses ____, not ____ as the template for copying

replicase, RNA, DNA

Replicases generate more…

mutations than DNA polymerases during replication, leading to antigenic variation that allows viruses to adapt to selective pressures

Influenza viruses

exhibit a type of antigenic variation called antigenic drift

Antigenic drift

where mutations occur in the genes of key viral surface proteins that are recognized by the immune system

Retroviruses (e.g., human immunoedificiency virus, HIV) encode the enzyme…

reverse transcriptase

Reverse transcriptase

an RNA-dependent DNA polymerase

After entering the host cell, reverse transcriptase uses the RNA genome as a…

template to make a DNA copy which integrates into the host cell chromosomes

Once integrated, the viral DNA may remain _____ or may be transcribed into RNA

latent

Viral DNA is…

traqnscribed into RNA then translated to make viral proteins then visions

Tumor

excessive cell growth via MITOSIS

Benign tumors

tumors that do not metastasize (spread) to other tissues

Malignant (cancerous) tumors

tumors that have the potential to metastasize

Control of normal cell growth includes

1. genes that stimulate cell growth

2. genes that inhibit cell growth

proto-oncogenes

genes that stimulate cell growth

tumor suppressor genes

genes that inhibit cell growth

_____ _______ are required for tumor formation

many mutations

Oncogene

proto-oncogene that has mutated sufficiently for a tumor to form

Some tumors are not caused by mutations, but by…

viruses (e.g., HPV)

What does the integration of HPV into host cell chromosomes do?

Changes proto-oncogenes to oncogenes (latent infection)

The viral genome codes for a ______ that stimulates excessive cell growth

protein

Plant viruses cause…

yellowing of foliage, irregular lines on leaves, flowers, and fruit

Prions

misfolded, nonfunctional proteins, that can transfer misfolded shape onto healthy proteins

When prions accumulate in _____ tissues they kill neurons, causing slow & fatal diseases

neural