Microbiology Exam 2 Unit 3

Front 1

How were viruses first discovered?

Back 1

• Filtration experiment: sick plant was ground up and then filtered; the lower half that didn’t contain bacteria still made the plant sick

Front 2

What is the best way to view a virus?

Back 2

· Best way to view a virus is with an electronmicroscope

Front 3

What are three general properties of viruses?

Back 3

· Extremely small particles

· All are obligate intracellular parasites (requiresa living host cell to replicate in)

· Very simple structure (nucleic acid enclosed ina protein shell)

Front 4

What is a genome and how does thegenome of a virus differ from that of a prokaryote or a eukaryote?

Back 4

· Genome: all the genetic information of anorganism

o Genome of a virus consists of DNA or RNA andnever both

Front 5

What are two unique genomicstructures found only in viruses?

Back 5

· Linear double stranded RNA

· Linear single stranded DNA

Front 6

Why do viruses need so few genescompared to prokaryotes and eukaryotes?

Back 6

· They sponge off their host using many of thecell’s normal cell processes and machinery

Front 7

What is a viral capsid? What is the role of the viral capsid and whatis it composed of?

Back 7

· Capsid: protein shell that all viruses have

o Surrounds and protects the genetic material ofthe virus

o All capsids composed of individual proteinsubunits called capsomeres

Front 8

How can capsids differ betweenviruses?

Back 8

· Capsids can be made up of a single types ofprotein capsomere, several types of protein capsomeres, capsomeres can be ofdifferent shapes and the number of capsomeres that make up the capsid maydiffer between viruses

Front 9

Where are viral spikes located andwhat is their function?

Back 9

· Viral spikes project from the capsid

· Their function was to promote viral attachmentto host cells

Front 10

What is a viral envelope? Where does the viral envelope originate fromand what is its function?

Back 10

· Viral envelope: capsid is covered by theenvelope in some viruses

o Envelope composed of phospholipid bilayer withcarbs and proteins, including viral spikes

o It is from the membrane of the eukaryotic cellthe virus infected and destroyed

o Envelope further serves to protect the geneticmaterial

Front 11

What is a virus called if it doesnot have an envelope?

Back 11

· A virus without an envelope is called a nakedvirus

Front 12

What are the four types of virusmorphology?

Back 12

·Helical viruses: capsids are rod-shaped and forma hollow helical structureo Nucleic acid of the virus is coiled into thecapsid· Icosahedron viruses: a 3 dimensional, 20 sidedfigure with 12 evenly spaced cornerso Nucleic acid is packed into the center of anicosahedron capsid· Enveloped helical or enveloped icosahedronviruses· Complex viruses:o Bacteriophages: viruses that infect bacteria. Capsids/heads are polyhedral shaped and containthe nucleic acid§ Tail sheath is helical

Front 13

How are viruses classified today?

Back 13

· Based on nucleic acid sequences and viralstructures

Front 14

What reasons might there be for the yearly increasein the number of virus species identified?

Back 14

Moving into areas where there are viruses we haven't discovered, drug resistance, and the viruses constantly mutate and change.

Front 15

What are the steps involved in theinfectious cycle of an animal virus?

Back 15

· Attachment: binding to host cell· Entry: getting into the host cell· Uncoating: disposing of the capsido Goal is to release the virus’s genomic materialinto the cytoplasm of the host cello How a virus enters the cell dictates the amountof uncoating required· Biosynthesis: replication of genetic materialand viral protein· Assembly: putting together new virus particles· Release: new virus particles leave the cell

Front 16

What is a susceptible host cell and what is ahost cell receptor?

Back 16

· Susceptible host cell: a cell that can beinfected by a virus

· Host cell receptor: a protein or glycoprotein onthe surface of the cell

o The receptor is required for normal cellularfunctions

Front 17

Definethe terms broad host range, restricted host range and tissue tropism

Back 17

· Broad host range: virus can infect manydifferent species because of a common receptor shared by many different specieso Rabies can infect humans, dogs, bats, …etc . Restricted host range: virus can only infect 1specific species because receptor is unique to 1 specieso Hepatitis B virus only infects humans· Tissue tropism: a virus that infects 1 specificcell type because receptor is unique to 1 type of cello Hepatitis B only infects liver cells

Front 18

Describes two ways that a virus canenter a host cell and explain what a virus needs to do in terms of uncoating after entering by each mechanism.

Back 18

· Entry by receptor-mediated endocytosis: can beused by naked or enveloped viruseso Virus is in a vesicleo Uncoating process:§ Vesicle must be broken down§ If virus is enveloped, envelope must be brokendown§ Viral capsid must be broken down· Entry by membrane fusion: virus capsid directlyinto cell cytoplasmo Can only be used by enveloped viruseso Uncoating process:§ Only viral capsid must be broken down

Front 19

Whatare three critical things a virus needs to do to make new virus particles

Back 19

· Replicate and make new copies of its genetic material

· Make new capsomeres for capsids

· Make new viral spike proteins

Front 20

Describethe assembly process for a naked virus and an enveloped virus

Back 20

· Naked Virus:o Putting the capsid together from capsomeresubunits and viral spikeso Getting the genetic material into the capsid· Enveloped virus:o Putting the capsid together from the capsomeresubunitso Getting the genetic material into the capsido Putting the viral spike proteins on the surfaceof the host cell plasma membrane

Front 21

Explain the two ways a virus can be released from an infected cell. In general, what types of viruses escape by each method

Back 21

· Cell lysis:o Too many new virus particles for the cell toholdo Cell bursts releasing new virus particles thatcan infect other cellso Naked and complex viruses are released by celllysis· Budding:o Only enveloped viruses released by buddingo Doesn’t immediately kill host cell

Front 22

Describe the difference between theinfectious cycle of an animal virus and a plant virus and explain why thisdifference is necessary.

Back 22

· First 2 steps of attachment and entry aredifferent in a plant virus

· Plant viruses must enter through an open woundor via a plant parasite or insect that carries the virus

Front 23

What are viruses that infectbacteria called?

Back 23

· Bacteriophages

Front 24

Describethe bacteriophage lytic cycle and what occurs at each step

Back 24

1) Attachment: binding to bacterial cell 2) Penetration: goal is to get the bacteriophage DNA into the bacterial cytoplasm o Problem is the bacterial cell wall (specifically peptidoglycan) Solution 1: phage lysozyme released at bacteriophage tail breaks down cell wall§ Solution 2: tail core driven through bacterialmembranes and DNA injected into cytoplasm· 3) Biosynthesis: making new bacteriophage to Replicate and make new copies of its geneticmaterial 4) Assembly: assembling the complete bacteriophage. 5) Release: phage lysozyme made within thebacterial cell weakens the cell wall

Front 25

Compare and contrast the bacteriophage lytic cycle with the infection cycle of ananimal virus

Back 25

The difference between the two is the first two steps. The animal virus attaches the viral spikes to the receptors, while with the bacteriophages its the tail fibers and the cell wall. Animal viruses uses endocystosis or membrane fusion, and bacteriophages just injects DNA or RNA material into the cytoplasm. The remaining steps are the same

Front 26

Namethe other infectious cycle a bacteriophage may go through and brieflyexplain/describe the steps of this cycle

Back 26

1)Attachment: binding to bacterial cell§ Requires a susceptible bacterium with a receptoron its membrane that a bacteriophage can bind too 2)Penetration: phage lysozyme released andbacteriophage tail breaks down peptidoglycan, then DNA from virus is injected. 3) Integration: bacteriophage DNA integrates into the bacterial chromosomeo 4) Replication: of bacterial chromosome andprophage DNA § Bacteria will grow and replicate its chromosomeincluding the prophage DNA in the chromosome§ 5) Excision of prophage DNA may be spontaneous or caused by exposure of bacterium to UV light

Front 27

What is a prophage?

Back 27

· Prophage: a bacterium that has bacteriophageintegrated into its chromosome

Front 28

How do you grow bacteriophage?

Back 28

· Grow a bacteriophage in bacteriao Bacteria + bacteriophage + melted agaro Bacteriophage will infect and kill a bacteriumas well as the bacteria in the immediate vicinity resulting in plaque (area ofclearing against a bacterial lawn)

Front 29

List the three ways you can grow ananimal virus.

Back 29

1) In animals:o Infect the animal with the virus and then“harvest” the virus when the animal becomes ill. Today animals are only used for unique viruses that cannot be grown by any other means 2) In embryonated eggs: Provides all the right conditions needed for viral replication. Only used for a small number of viruses. 3) In cell culture:o The simple and easiest way to grow viruses in alaboratory setting

Front 30

What are primary cell lines? What are continuous cell lines?

Back 30

· Primary cell lines: cells from freshly isolatedtissue that have a finite period of life· Continuous cell lines: cells from canceroustumors that continually divide and are immortal

Front 31

What are cytopathic effects and a cell monolayer? How can you tell if a virus is growing incell culture?

Back 31

· Cytopathic effects: cell deteriorationo Tissue culture cells are grown on speciallytreated plastic plateso Cells will grow and spread out across the plateo When the entire bottom of plate is covered withcells a monolayer has been formed (equivalent of bacterial cell lawn)o You can tell if a virus is growing in a culturebecause there will be plaques of viruses that have destroyed the cells in thatarea

Front 32

Listthe five types of viral infections and provide an example (name of a virus orviral disease) for each

Back 32

· Acute infection with low mortality:o Short time for the virus to be cleared (not sickfor long)§ Coldo Acute infection with high mortality:§ Short time for virus to kill its host§ Ebola o Persistent or chronic infection:§ Occurs gradually over a long period of time§ Potentially debilitating or fatal§ Hepatitis, HIVo Latent infections:§ Virus remains dormant in our body butoccasionally is re-activated§ Cold sores, shingleso Oncogenic infection: viruses that integratetheir genetic material into the host cell’s DNA, which can lead to cancer§ HPV