BIO 221- Genetics of Viruses

Are viruses living agents?

NO!!

What are the characteristics of viruses?

Non-cellular

No metabolism

No energy use

Does not maintain homeostasis/reproduce

Do viruses use energy?

No!!

Do viruses maintain homeostasis or reproduce?

No!!!

Are viruses cellular?

No!!!

What do host cells require to replicate?

A host cell

What does the structure of a simple virus consist of?

Protein coat (capsid)

What does the capid of a simple virus surround?

The viral genome

What are simple viruses also calledd

Naked viruses

What shape can capsids take?

Helical, polyhedral, or complex

What surrounds the capsid of an enveloped virus

Lipid bilayer or envelope

What does the envelope of an enveloped virus contain

Glycoprotein spikes

What are the protein subunits of capsids calledd

Capsomers

How do viruses attach to a host?

The viral ligand binds to the host’s cell receptor

What mechanisms do viruses use to enter a host

1. Injection of viral genome

2. Endocytosis

3. Fusion

4. Integration

What happens when a bacteriophage injects itself into the host

Leaves behind shell

What type of viruses inject into a host

Bacteriophage

What happens when enveloped viruses and naked viruses enter a host

Entire virus enters the cell

What type of viruses enter a host through endocytosis

Enveloped and naked viruses

What happens when an enveloped virus enters a host

Fusion

What type of virus uses fusion to enter a host

Enveloped

What protein must viruses have to use integration

The integrase enzyme

What virus uses integration

Lysogenic (Temperate) bacteriophage (prophage)

How is RNA converted to DNA?

Reverse transcriptase

What does it mean to synthesize viral components

1. Temporal expression of viral genes

2. Replication of viral nucleic acid

3. Use of host cell enzymes and components

How are viruses released from the host cell

1. Lysis of host cell

2. Budding

   1. Exocytosis

What type of viruses use budding

Enveloped viruses

In the “Reproductive cycle of phage”, where does the virus bind to

Proteins in the outer bacterial cell membrane

In the “Reproductive cycle of phage”, what does the virus inject into the bacterial cytoplasm

DNA

In the “Reproductive cycle of phage”, where is the virus’s DNA injected into

The bacterial cytoplasm

In the “Reproductive cycle of phage”, how does the virus DNA integrate into the bacterial chromosome

Via integrase

In the “Reproductive cycle of phage”, what does the host cell carry

A prophage

In the “Reproductive cycle of phage”, how is the lysogenic cycle ended

Switch to lytic, prophage DNA excised

In the “Reproductive cycle of phage”, what is the alternative way to end the lysogenic cycle

The reproductive cycle may completely skip the lysogenic cycle

What viruses only have reverse transcriptase?

Retroviruses

In “Reproductive cycle of HIV”, how does the retrovirus attach to the host cell

Spike glycoproteins bind to receptors on the plasma membrane

In “Reproductive cycle of HIV”, how does the virus enter the cell

Viral envelope fuses with host cell membrane—>Releases capsid and contents into cytosol

In “Reproductive cycle of HIV”, what is released into the host

Viral RNA, reverse transcriptase, and integrase

In “Reproductive cycle of HIV”, how are some capsid proteins removed

Removed by cellular enzymes, aka ‘uncoating’

What is the process that includes cellular enzymes removing capsid proteins

Uncoating

In “Reproductive cycle of HIV”, what is the viral RNA reverse transcribed into

Double-stranded DNA

In “Reproductive cycle of HIV”, what happens after the viral RNA is reverse transcribed

It is integrated into the host cell via integrase

In “Reproductive cycle of HIV”, how long may an integrated provirus remain latent

Long period of time

In the “Reproductive cycle of phage”, how is the virus synthesized

Phage DNA circulates, host chromosomal DNA is degraded

In the “Reproductive cycle of phage”, how are the viruses assembled

Assembled with help of non-capsid proteins to make new phages

In the “Reproductive cycle of phage”,

Lysozyme (viral enzyme) causes host cell lysis, new phages released from exploded cell

In “Reproductive cycle of HIV”, how is the virus synthesized

Proviral DNA directs synthesis of viral components

In “Reproductive cycle of HIV”, how is the virus assembled

Capsid proteins enclose 2 RNA molecules + molecules of reverse transcriptase + integrase

In “Reproductive cycle of HIV”, how does the capsid assemble

Uses spike glycoproteins during budding

In “Reproductive cycle of HIV”, how does the virus release

Virus buds from plasma membrane

In “Reproductive cycle of HIV”, what is the new viral envelope derived from

A portion of the host cell membrane

What can temperate bacteriophage undergo or establish

Can undergo lytic replication or establish lysogeny

What is lysogeny

State of bacterial chromosome containing bacteriophage DNA

What does lysogen require

Integrase enzyme

What is a non-temperate bacteriophage called

Lytic bacteriophage

What is a lysogen

Cell in the state of lysogeny

What is a prophage

Integrated bacteriophage in DNA

What happens when lysogeny is established

No bacterial cells are made, when bacterial cell replicates, virus is also replicated

How long can lysogeny persist

Indefinitely

What will happen to lysogeny if the bacterial cell undergoes stress

Lysogeny ends

In latency of animal viruses, what are the two ways human viruses can establish latency

Integration and with episomes

What is an episome

Extrachromosomal organism that replicates independently of the host cell chromosome and integrate into the host chromosome

What are virioids

Single-stranded, circular RNA molecules

What are the characteristics of viroids

Lack proteins, infect plants

What are prions

Infectious proteins that cause neurodegenerative diseases

What do prions cause

Neurodegenerative diseases

What is the first step in replicating prions

Abnormal prion interacts with normal prion

What is the second step in replicating prions

Normal prion is converted to abnormal prion

What is the third and fourth step in replicating prions

Abnormal proteins continue to infect normal proteins until all normals are converted to abonormals

How specific is prion replication

Species specific

How long is the incubation of prions

Months to years

What can prions cause

Spongy appearance

What are encephalopathies

Transmissible spongiform prions