Viruses

Virus

Infectious particle consisting of little more than one or more molecules of nucleic acid enclosed in a protein coat

Viral genomes can consist of

double/single-stranded DNA

double/single-stranded RNA

Capsid

protein shell enclosing the viral genome

What are capsids made out of?

protein subunits called capsomeres

Viral envelopes

membranous envelopes that help viruses infect hosts.

contain both viral and host molecules

Bacteriophage

viruses that infect bacteria

Obligate Intracellular Parasite

The virus must live and reproduce inside a host cell—it can’t replicate or do anything on its own.

Host range

A limited number of host species that it can infect

When does viral infection begin?

When a virus binds to a host cell, and the viral genome enters the cell

Generally, what does a virus do after entry in a host?

replicate inside of the host using the host’s own organelles. they then burst out of the cell

What are the replicative cycles of phages?

lytic cycle

lysogenic cycle

Lytic cycle

phage replicative cycle, results in death of the host cell.

Virulent phage

A phage that can reproduce only through the lytic cycle

What cycle is this?

The Lytic cycle

Lysogenic cycle

replicates the phage genome without destroying the host

Temperate phage

A phage that uses both the lytic and lysogenic cycle

What happens in the lysogenic cycle?

Viral DNA integrates with the host’s DNA and replicates within the host cell. Can remain dormant for a long time until triggered to enter the lytic cycle

Prophage

Viral DNA that is integrated into a bacterial cell’s genome

Restriction enzymes

cuts specific DNA sequences; protects the bacteria from viral DNA

How does bacteria prevent itself from cutting up its own DNA?

The bacteria methylates its DNA at the recognition sites

What is the CRISPR-Cas system and how does it protect bacteria?

Stores viral DNA sequences and uses RNA-guided Cas proteins to recognize + cut matching viral DNA in the future. Kind of like a bacterial immune system

What are the two key variables used to classify viruses that infect animals

DNA or RNA

Presence or Absence of an envelope

How can viruses use their envelopes to enter host cells?

Glycoproteins from the envelope bind to specific receptor molecules on the host cells surface

Budding

Enveloped viruses exit the host cell by pushing through the membrane, taking a piece of it as their envelope, often without killing the cell.

What is this

The Replicative Cycle of an Enveloped RNA Virus

Where is the broadest variety of RNA viruses found?

Viruses that can infect animals

What are positive-sense RNA viruses?

capable of operating as mRNA and can be directly translated into the protein in the host

Retrovirus

Use reverse transcriptase to copy their RNA genome into DNA

What retrovirus causes AIDS?

HIV

Provirus

Viral DNA that is integrated into the host genome

What is the difference between a provirus and a prophage?

prophage is for bacterial cells, provirus is for eukaryotic cells

How do retroviruses replicate?

virus enters host cell

reverse transcriptase makes DNA from RNA

Viral DNA integrates into host DNA
host cell transcribes viral genes

new viruses are assembled and released

Do retroviruses go through the lytic cycle?

No. The only thing that leaves the host cell is a new virus that buds from the host cell.

When did viruses likely evolve?

After cells appeared, since they need hosts to replicate.

What are possible sources of viral genomes?

Plasmids (circular DNA) and transposons (mobile DNA segments)—both can move between cells.

How do viruses damage or kill animal cells?

By triggering the release of hydrolytic enzymes from lysosomes.

How do viruses cause disease symptoms?

They may cause cells to make toxins or contain toxic components like envelope proteins.

What causes many viral infection symptoms?

The body’s own immune response, not the virus directly.

Vaccine

Harmless derivative of a pathogen

Stimulates the immune system to mount defenses against the harmful pathogen

What do antibiotics target?

Enzymes specific to bacteria; they are powerless against viruses

What do antiviral drugs do?

They help treat—but do not cure—viral infections

Why are receptor proteins important in viral infections?

They’re targets for treatment or prevention; viruses use them to enter cells.

What does the SARS-CoV-2 vaccine target?

The virus’s spike protein, which binds to host receptors.

What receptor does HIV mainly use to enter cells?

CD4 protein.

How is CCR5 used in HIV treatment?

Drugs can block or mask CCR5 to prevent HIV from binding and entering cells.

Emerging viruses

Viruses that suddenly become apparent

Can be common in a local population, but spread rapidly when introduced outside of that population

Epidemic

general outbreak within a community. could be a new disease or an existing one, but if there is a large increase in a general population

Pandemic

Global outbreak of disease → global epidemic

How did the chikungunya virus spread?

Through mosquitoes

What contributes to the emergence of viral diseases

Mutation of an existing virus

Spread from a small, isolated population

Spread from animal populations

The less similar an animal is to a human, the ______ deadly the disease is to humans

more

Which influenza strain has caused 4 major pandemics in the last 100 years (as of may 2025)

Influenza A

Which influenza strain(s) only infect humans?

B and C

Netting

Form of vector control in public health

Put a barrier between humans and virus-carrying mosquitoes

Prion

Infectious, misfolded protein

What can cause degenerative brain diseases in many animal species

Prions

Prions act very ______

slowly. incubation period of at least 10 years

Are prions destructable

fuck no. they resist heat and radiation and enzymes and stuff

Prion transmission

food, contamination, sometimes genetics

whats the cure for prion diseases?

youre fucked actually there is none

What happens after you denature a prion?

it refolds…

Creutzfeldt-Jakob Disease (CJD)

most common prion disease; causes rapid neurodegeneration

Fatal Familial Insomnia

inherited prion disease; causes progressive insomnia, then death

Kuru

prion disease espread by ritual cannibalism in Papua New Guinea

Bovine Spongiform Encephalopathy (BSE)

“mad cow disease” - caused by prions

How do prions infect other proteins?

By binding to normal proteins and causing them to misfold, triggering a chain reaction that leads to protein clumps and brain damage.