BIO 205 Chapter 12: Viruses

What is the third step of Influenza virus replication?

-ssRNA enter nucleus

How many viruses are there on earth?

1*10^31 viruses on the planet. A considerable amount are human pathogens.

What is a Bacteriophage life cycle (lytic and lysogenic)?

1. Attachment 2. Insert genome and circularize DNA 3. If it takes a lytic path... a. Synthesizes capsid and copy genome b. Package DNA into capsid c. exit via host cell lysis 3. If it takes a lysogenic path... a. DNA incorporate into host genome b. replicate with host *Stress induced excision of phage DNA

What is the first step of HPV replication?

1. Bind to host receptors - enter the host cell via endocytosis

What are the four major shapes of viruses?

1. Filamentous (eg. TMV, helical capsid protein coat) can be enveloped or naked 2. Icosahedral head (eg. radial symmetry, herpes simplex virus, adenovirus, rhinovirus) can be enveloped or naked. 3. Complex Head-tail (eg. icosahedral head with filamentous tail connected with tail fibers) 4. Amorphous (eg. looks like a pill shape, carries its own viral enzymes)

What is the first step of Influenza virus replication?

1. HA bind to host sialic acid

What is viral recombination (Influenza Antigenic Shift)?

1. Human 2.6 sialic acid 2. Birds 2,3 sialic acid 3. Pig 2.3 & 22.6 sialic acids

Why are viruses difficult to treat?

1. Viruses are bad at replicating their genomes without errors (ie. mutations) 2. Not a lot of targets 3. Extremely diverse genomes 4. if you target the virus, you have to target the host.

What causes someone to experience different severity of a particular virus?

1. age 2. immune system

Protections against HPV

1. condoms - partial 2. Gardasil - vaccine - reccomended prior to sexual activity

What is contained in a viral envelope?

1. host cell membrane upon release 2. viral proteins- spikes proteins for attachment to a new host cell.

What is the viral structure?

1. nucleic acid (dna or rna, double or single stranded) rarely both 2. Capsid - protein coat; self assembly 3. Envelope - optional, some viruses have it; lipid bilayer (cell membrane) always comes from host cell.

What structures are in the influenza virus cell?

1. nucleocapsid coats each RNA segment 2. Matrix proteins 3.cap, RNA dep.,RNA polymerase 4. Envelope - bud off host cell membrane 5. HA - hemagglutinin 6. NA - neuraminidase

What are some virus characteristics?

1. particlee 2. metabolically inactive 3. require host cell to produce

Viral classification is based on

1. the genome which is usually very small (some are slightly large) 2. Baltimore Model - classifies based on genome type (ie. DNA, RNA, double stranded, or single stranded) - How virus gets into mRNA

What is the second step of HPV replication?

2. Viron travels to nucleus

What is the second step of Influenza virus replication?

2. Viron uptake via endocytosis - release viral particles via fusion

What is the third step of HPV replication?

3. Genome uncoated in nucleus

What is the fourth step of HPV replication?

4. Viral DNA uses host RNA polymerase for transcription to mRNA

What is the fifth step of HPV replication?

5. mRNA translated to viral proteins (capsid, spike) in cytoplasm

What is the sixth step of HPV replication?

6. capsid imported into nucleus and DNA packaged into capsid

What is the seventh step of HPV replication?

7. Shed off with epithelial cells. *can enter lysogenic cycle - transform host cell into cancer cell oncogenes E6 & E7 (cell replication)

How many adults are affected by HPV?

80%

How does the term "virion" differ from a virus?

A virion refers specifically to the structure of the virus particle.

Describe class four Baltimore Model.

+ ssRNA to - ssRNA to mRNA

Describe class six Baltimore Model.

+ ssRNA to DNA to mRNA via reverse transcriptase from step one to two

What is the difference between positive and negative sense RNA used in the Baltimore Model?

+ss RNA is direct to protein -ss RNA is direct to capsid to +ss RNA to protein *RNA dependent on RNA polymerase

Describe class five Baltimore Model.

- ssRNA to mRNA

What does HPV look like?

-small; icosahedral -naked -ds DNA -8kb -8 genes -Baltimore class: 1

What is a oncogenic virus?

At least six viruses have been found to cause human cancer like HPV.

What is neuraminidase?

Cleaves sialic acid - entry and exit.

Case study 1: Genital Warts from a Virus 1. HPV - ds DNA virus, oncogenic

Genital warts are caused by HPV. Doctor said it will most likely go away on their own. Some HPV strains stay asymptotically and cause cancer.

What is contained in the 2019-2020 flu shot?

H1N1, H3N2 (influenza A), Two B viruses - predicted

What is the sixth step of Influenza virus replication?

HA/NA enter ER/Gogi & transported to host cell membrane

What is sailic acid used for?

Harmful bacteria, viruses, and other pathogens use cell surface carbohydrates as sites for recognition and binding to their target host cell, the first step in infection.

How do viruses reproduce?

Viruses can reproduce only by infecting living cells. 1. They attach to the host cell 2. Genome entry uncoating 3. Assembly 4. Release

What is antigenic drift?

a mechanism for variation in viruses that involves the accumulation of mutations within the genes that code for antibody-binding sites. Subtle changes in the H & N such that the virus is new to the immune system - seasonal flu

What is a virus?

a tiny, nonliving, particle that enters and reproduces inside a living cell. Its genome is contained within a capsid (protein coat).

What does bacteriophage translate to?

bacteria eaters

What has HPV been linked to?

cervical cancer - 2008 Nobel prize

Human Rhinovirus causes what?

common cold; usually moderate

what are inclusion bodies?

compacted masses of viruses or damaged cell organelles in nucleus and cytoplasm

Describe class one Baltimore Model.

dsDNA to mRNA

Describe class seven Baltimore Model.

dsDNA to mRNA to dsDNA via reverse transcriptase from step two to three.

Describe class three Baltimore Model.

dsRNA to mRNA

What are the Serotypes of Influenza A?

epidemics and pandemics. Birds and mammals may serve as reservoirs for infection. Undergo major antigenic changes.

What does the influenza virus look like?

flu - nucleocapsid - ssRNA - Baltimore class 5 -8 RNA genome segments

What is syncytia formation?

fusion of multiple host cells into single large cells with multiple nuclei - Viruses fuse the cell membranes (abnormally large cell).

What are the Serotypes of Influenza C?

lack NA, late

What are the Serotypes of Influenza B?

seasonal virus, low chages

Describe class two Baltimore Model.

ssDNA to dsDNA to mRNA

How do viruses replicate?

using their host cells machinery 1. Host recognition/ attachment (viral & host receptors & co-receptors) 2. Entry & uncoating 3. Assembly 4. Release from host cell

What is a cloning vector and how are bacteriophages considered cloning vectors?

Bacteriophages are routinely as cloning vectors, small genomes into which foreign genes can be inserted and cloned for gene technology.

What is the Baltimore Classification?

Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their nucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), Sense, and method of replication. https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/9%3A_Viruses/9.3%3A_Classifying_Viruses/9.3B%3A_The_Baltimore_Virus_Classification

What is the ninth step of Influenza virus replication?

Bud off host cell (destroy host cell) - take envelope from host membrane

Describe the chronic latent state.

Has periodic reactivation, herpes, and HIV

What is the influenza virus?

Influenza is a viral infection that attacks your respiratory system — your nose, throat and lungs. Influenza is commonly called the flu. Usually people can resolve on their own.

Lytic vs Lysogenic

Lytic is the active form of a virus when it is taking over host cells Lysogenic is viral DNA incorporated into hosts but is dormant until stress or some other stimulant.

What is antigenic shift?

Major change in genetic set up of the flu virus. a recombination (gene assortment) between avian and mammalian strain.

What is an ocogene?

Normal cell regulatory gene (human) is modified to replicate out of control = cancer

How do viruses gain an envelope?

Once the virus entered a cell it exits the cell by budding off the cell. So it takes some of the cell tissue with it.

What is the seventh step of Influenza virus replication?

Package/Assemble RNA segments (NC/NP) exit nucleus

What are the functions of a capsid & envelope?

Protect nucleic acids from host enzymes and environment.

What is the causative agent of strep throat?

Streptococcus pyogenes - bacterial Gram positive, thick peptidoglycan layer - Antibiotics that target peptidoglycan (e.g. penicillin that attack cell wall) will not work against viruses. In order to stop a virus from replicating, you will have to harm the host cell because the virus uses the host to survive.

What is tropism?

Tissue tropism is the cells and tissues of a host that support growth of a particular virus or bacterium. Some bacteria and viruses have a broad tissue tropism and can infect many types of cells and tissues. Other viruses may infect primarily a single tissue. wikipedia

What is the fourth step of Influenza virus replication?

Transcription of the nucleus -ssRNA and +ss

What is the fifth step of Influenza virus replication?

Translation in cytoplasm using host ribosomes

What is hemagglutinin?

Trimer, main determinant of virulence - Binds to sialic acid

True or False: Tumors may be malignant or benign - malignant cells spread via metastases.

True

What was the first virus ever discovered?

Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus.

What is transformation?

Viral nucleic acids incorporate into host chromosome - host cells have increased growth rates, chromosomal changes, and changes in surface chemistry. These "oncoviruses" can cause cancer.

What is the eighth step of Influenza virus replication?

Viron assembles in cytoplasm

What is the host range of a virus?

the spectrum of host cells a virus can infect ex: SIV affects Great apes HIV affects humans only