Chap 21: Viruses

Are viruses alive? Why or why not?

No - Can't reproduce without a host cell, doesn't undergo cellular metabolism, use energy, etc

What are viruses made of?

Capsid protein and nucleic acid

What are the four shapes do viruses come in?

Helical
Icosahedral
Enveloped
Head-and-tail

What capsids are long and cylindrical. Many plant viruses are helical, including TMV?

Helical

What capsid virus has shapes that are roughly spherical, such as those of poliovirus or herpesviruses?

Icosahedral

What capsid virus has membranes derived from the host cell that surrounds the capsids. Animal viruses, such as HIV, are frequently enveloped?

Enveloped

What capsid virus infects bacteria and have a head that is similar to icosahedral viruses and a tail shaped like helical viruses?

Head-and-Tail

What is different about enveloped viruses?

They have membranes derived from the host cell

True or False:
Viruses can have either RNA or DNA nucleic acid.

True

T or F:
Their nucleic acid can be double stranded or single stranded (It may also be liner or circular)

T

How are DNA viruses different from RNA viruses?

DNA viruses directs the host cells replication proteins to synthesize new copies of the viral genome, RNA viruses contain only RNA genetic material

Which nucleic acid types require an intermediate between the viral nucleic acid and mRNA transcription?

Group 4, 5, 7

Group 1 (DNA Virus)

has double-stranded DNA (dsDNA) as their genome. Their mRNA is produced by transcription in much the same way as with cellular DNA, using the enzymes of the host cell

Group 2 (DNA Virus)

has single-stranded DNA (ssDNA) as their genome. They convert their single-stranded genomes into a dsDNA intermediate before transcription to mRNA can occur

Group 3 (RNA Virus)

has dsRNA as their genome. The strands separate, and one of them is used as a template for the generation of mRNA using the RNA-dependent RNA polymerase encoded by the virus

Group 4 (RNA Virus)

has ssRNA as their genome with a positive polarity, which means that the genomic RNA can serve directly as mRNA. Intermediates of dsRNA, called replicative intermediates, are made in the process of copying the genomic RNA. Multiple, full-length RNA strands of negative polarity (complementary to the positive-stranded genomic RNA) are formed from these intermediates, which may then serve as templates for the production of RNA with positive polarity, including both full-length genomic RNA and shorter viral mRNAs.

Group 5 (RNA Virus)

contain ssRNA genomes with a negative polarity, meaning that their sequence is complementary to the mRNA. As with Group IV viruses, dsRNA intermediates are used to make copies of the genome and produce mRNA. In this case, the negative-stranded genome can be converted directly to mRNA. Additionally, full-length positive RNA strands are made to serve as templates for the production of the negative-stranded genome

Group 6 (Retrovirus)

Reverse transcription into -ssDNA, which is then used to make its own complementary +ssDNA, yielding dsDNA, which is inserted into host DNA.Then used to transcribe +mRNA

Group 7 (Retrovirus)

dsDNA transcribed to +ssRNA (that can act as +mRNA).This +ssRNA then undergoes reverse transcription to create –ssDNA.This –ssDNA is then used to make its own complementary +ssDNA, yielding dsDNA.This dsDNA is then inserted into host DNA. Then used to transcribe +mRNA

How are retroviruses different?

Each virion contains two complete copies of the single-stranded RNA genome.

What is a retrovirus?

any of a group of RNA viruses that insert a DNA copy of their genome into the host cell in order to replicate

How do virus recognize, enter and infect host cells?

Attachment
Penetration
Uncoating
Replication
Assembly
Release

What do you call a Specific host cells that a virus must occupy and use to replicate?

Permissive

What is the difference between lytic viral life cycle and lysogenic viral life cycle?

Lytic kills the host, whereas Lysogenic just infects it

What virus is known for attacking bacteria?

bacteriophages

An infection is said to be ________, When infection of a cell by a bacteriophage results in the production of new virions?

Productive

If the virions are released by bursting the cell, the virus replicates by means of...?

Lytic Cycle

When a temperate bacteriophage infects a bacterial cell, it replicates by means of a ...?

Lysogenic Cycle

How do viruses recognize the host cell?

glycoproteins on surface of capsid

True or False:
Lysogenic cycle is the same as viral latency.

False

What is a host range?

the spectrum of host cells a virus can infect

How is host range determined?

by specific host attachment sites and cellular factors

How do viruses recognize their host cells?

surface proteins

What role do glycoproteins play in host cell recognition?

allow cells to identify each other, communicate, and interact

What are the two types of viral transmission?

Horizontal and Vertical

From one organism to another (Hint: Occurs in all viruses)

Horizontal Transmission

From parent to offspring (Hint: Occurs almost exclusively in plants•In Humans, HHV-6 is transmitted vertically)

Vertical Transmission

What is relationship between viruses and vaccines?

Vaccines work by teaching the immune system to recognize and build immunity to specific viruses or bacteria

Tru or False:
virus cannot penetrate cell wall unless the cell wall is damaged

Tru

Do animals have a cell wall

No (virus can more easily infect them)

Are plants viral infections secondary to mechanical damage?

Yes

What is the relationship between viruses and antibiotics?

Antibiotics do NOT work on viral infections

What type of nucleic acid does the flu have?

-ssRNA

What type of nucleic acid does the COVID-19 have?

+ssRNA

What type of viruses are the flu and COVID-19 ?

Enveloped

How is the flu and COVID-19 not the same virus?

The flu has a spherical capsid, and COVID-19 has a helical capsid