Term
| -Viruses -Virology -Virologists |
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Definition
| -acellular infectious agents. -Study of viruses -Scientists who study viruses |
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Term
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Definition
| -have no cells-acellular biological entity -cant reproduce independent of cells, and don't carry out cell divisions as prokaryotes and eukaryotes do. -generally only have one type of nucleic acid:DNA or RNA, not both |
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Term
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Definition
| - a complete virus particle -consist of one or more molecules of either DNA or RNA enclosed in a coat of protein. -May have additional layers: lipid, carbohydrate, proteins(considered an enveloped virus) |
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Term
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Definition
| 1.Attachment(also called absorption) 2.Viral entry:internalization of capisds and/or translocation of genetic material. 3. Synthesis of genetic materials and proteins. 4. Assembly of progeny virus particles. 5. Release of virions |
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Term
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Definition
-Suitable animal hosts
-Embryonated eggs
-tissue(cell)cultures
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Term
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Definition
-plant tissue cultures
-plant protoplast cultures
-whole plants |
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Term
| Bacterail and Archaeal Viruses |
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Definition
| -usually cultivated in broth or agar cultures of actively growing bacteria |
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Term
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Definition
| -microscopic or macroscopic degenerative changes or abnormalities in host cells or tissues. |
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Term
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Definition
-Local areas of cellular lysis or cytopathic effects
-Determines the amount of vviruses by counting the plaques th3ey form on the host cells: measure infectivity of viruses. |
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Term
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Definition
a) Nucleic acid type (DNA or RNA)
b)Nucleic acid strandedness(double stranded or single stranded)
c)Sense of ssRNA genomes(positive or negative)
d)Structural features:presence or absence of envelope, capsid symmetry, dimensions of virion and capsid
e)other propertes such as host range |
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Term
-Double stranded DNA
-Singel stranded DNA
-dsRNA
-ssRNA |
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Definition
-Herpes virus and many bacteriophage
-Parovirus
-rotavirus, blue-tongue virus
-positive stranded RNA(polio-virus,rhino-virus)
-negative stranded RNA(influenza virus,Ebola virus)
-positive stranded RNA with DNA steps(retrovirus:HIV) |
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Term
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Definition
| -Order(virales), Family(viridae),subfamily(virinae), genus and species(virus) |
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Term
Architecture of Viruses
-Nucleic Acid
-Capsid
-Envelope |
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Definition
-Nucleic acid: One or mutiple molecules of DNA or RNA genome
-Capsid: A protein shell consisting of many copies of capsid protein (coat protein) subunits and enclosing the genome.
-Enveloped or non-enveloped: May be enveloped by a lipid bilayer(membrane) |
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Term
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Definition
-electron microscopy, electron tomography, and X-ray crystallography.
-Using Electron microscopy and electron tomography, you can see the shape of virus particles, but you won’t see much detail.
-X-ray crystallography is the only technique to produce atomic structures of viruses. Virus structure determination by X-ray crystallography is still a challenge. Electron cryo-microscopy (cryoEM) is an emerging powerful technique for visualization of virus structures.
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Term
Structural requirements imposed by virus life cycles:
Genetic economy? |
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Definition
-Formation of a closed shell to protect genetic materials.
-Genetic economy: the amount of genetic information is minimized
-A single or very few types of coat proteins.These protein subunits repeat a number of times to form the virus capsid.Formation of the capsid by these repeating units is governed by symmetry. |
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Term
What size are most viruses?
What is a Mimivirus? How many base pairs? How lare in diameter? How many proteins does it encode for? |
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Definition
| Viruses are tiny compared to bacteria. Most are around 10-100 nm across. We mentioned Mimivirus, a giant virus that infects Amoeba, which is the very largest virus known to date. It’s ~5000 A in diameter, and contains a 1.2 million bp genome that encodes >900 proteins, which makes it bigger than some smallest bacteria. |
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Term
What is Icosahedral symmetry? |
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Definition
-Many viruses or virus capsids display icosahedral symmetry
-Icosahedral symmetry is the most efficient way to make a closed shell using a single or very few types of proteins to achieve largest possible size and volume for encapsulation of viral genetic materials. |
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Term
-Can we directly couint the number of virus particles on an elctron microscope?
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Definition
| We can directly count the number of virus particles on an electron microscope. Hemagglutination assay can be performed on viruses that contain hemagglutinin on their surface. |
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Term
(more complex virus capsid)
what is a:
Capsomer?
Pentamer ?
Hexamer? |
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Definition
Capsomer: Ring-shaped unit made of 5 or 6 protomers
Pentamer (penton): 5-subunit capsomer
Hexamer (hexon): 6-subunit capsomer
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Term
| Icoshedral viruses more information |
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Definition
| For the icosahedral viruses, we mentioned a few key terms. Capsomer is a ring-shaped unit made of 5 or 6 subunits. There are two types of capsomers: pentamer (penton), and hexamer (hexon). An icosahedral capsid can be viewed as an assembly of pentamers and hexamers. |
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Term
What do Adenoviruses contain?
what do mayn bacterial viruses have?
What are envelopes made out of and what do they surround? |
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Definition
| Adenovirus contains fibers on their 5-fold vertices, and many bacterial viruses have tails. Enveloped viruses contain a lipid bilayer surrounding the capsid. |
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Term
What cylce do Virulent phages go under?
What is that cylcle?
What is burst size? |
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Definition
-Virulent phages go under lytic cycle
–phage life cycle that culminates with host cell bursting, releasing virions
Burst size: the number of viruses produced per infected cell |
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Term
What cylce do Temperate phages go under?
What does this cylce do? |
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Definition
Temperate phages have two reproductive options either to
reproduce lytically as virulent phages does, or to remain within the host cell without destroying it. |
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Term
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Definition
-Receptors are specific surface structures on host to which viruses attach.
-They are specific for each virus and can be lipopolysaccharide, proteins, etc. |
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Term
| What is a T4 phage? What does it do and how? |
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Definition
-Phage T4 infect E.coli by using long tail fiber that binds to E. coli lipopolysaccharide or OmpC.
-Tail fibres allow attachment to a host cell, and the T4’s tail is hollow so that it can pass its nucleic acid to the cell it is infecting during attachment. |
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Term
What is the life cycle of the T4 phage?
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Definition
| •Adsorption and penetration (starting immediately) •Arrest of host gene expression (starting immediately) •Enzyme synthesis (starting after 5 minutes) •DNA replication (starting after 10 minutes) •Formation of new virus particles(starting after 12 minutes) - After the lifecycle is complete, the host cell bursts open and ejects the newly built viruses into the environment, destroying the host cell. T4 has a burst size of approximately 300 viral particles per infected host. |
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Term
| What are the steps of T4 virus penatration? |
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Definition
a)landing
b)attachment
c)Tail contraction
d)Penetration and unplugging
e)DNA injection |
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Term
| Events that occur in life cylce of T4 phage?(TANG WRITTEN STUFF) |
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Definition
| A series of sequential events take place during T4 infection. These include: -attachment to specific receptor on host cell -penetration of the cell wall -insertion of the viral nucleic acid into the host cell -transcription and translation of early mRNA results in production of proteins and enzymes involved in phage DNA synthesis -phage DNA replication by the phage encoded replisome -transcription and translation of late mRNA results in synthesis of capsid proteins, proteins required for phage assembly and proteins required for cell lysis and phage release |
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Term
How do dsDNA viruses synthesize proteins and nucleic acids?(such as T4Phage) |
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Definition
- dsDNA viruses use their DNA genome as a template for mRNA synthesis then the mRNA is translated to produce viral proteins using the host RNA polymerase. |
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Term
| what does hydroxymethyl-cytosine (HMC) look like? |
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Definition
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Term
What is hydroxymethyl-cytosine (HMC)?
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Definition
5-Hydroxymethylcytosine is a DNA pyramidine nitrogen base. It is formed from the DNA base cytosine by adding a methyl group and then a hydroxy group. It is important in epigenetics, because the hydroxymethyl group on the cytosine can switch a gene on and off. It was first seen in bacteriophages in 1952. However, it was recently[when?] found to be abundant in human and mouse brains,as well as in embryonic stem cells. |
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Term
T4 gene expression is temporally regulated. What does transcription of early mRNA do? What does transcription of late mRNA do?(T4 life cylce) |
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Definition
C)insertion of the viral nucleic acid into the host cell. D)transcription à early mRNA E)translation of early mRNA results in production of proteins and enzymes involved in phage DNA synthesis. F)phage DNA replication by the phage encoded replisome. G)transcription à late mRNA H)translation of late mRNA results in synthesis of capsid proteins, proteins required for phage assembly and proteins required for cell lysis and phage release. I) phage assembly J)cell lysis and phage release
A)attachment to specific receptor on host cell. B)penetration of the cell wall.
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Term
| How are T4 phage particles released? How does the T4 lysozyme reach the cell wall? |
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Definition
-Two proteins are involved. The T4 lysozyme attacks the peptidoglycan of the E. coli cell wall
-Another phage encoded protein holin creates holes in the E. coli plasma membrane, allowing the T4 lysozyme to move to the cell wall.
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Term
What options do Temperate phages have? |
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Definition
They have two reproductive options either to reproduce lytically as virulent phages do, or remain within host cell without destroying it. |
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Term
| What happens during the lyctic cylce(generally)? |
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Definition
| Phage DNA is injected into the cytoplasm of the cell. The phage DNA directs synthesis of many new phages. The cell lyses(breaks down) and the new phages can bind to other bacterial cells. |
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Term
| What happens during lysogenic cylce(generally)? |
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Definition
| The phage injects its DNA into the cytoplasm of the cell. The phage DNA integrates into the host chromosome. The prophage DNA is copied when the cell divides. This allows for the virus to be passed onto all other copies of the cell. Exposre to sress such as UV light, lack of oxygen ect. triggers exission from the host chromosome. The phage then becomes lyctic and starts synthesis of many phages and the cell lysis and the phages exit the cell. |
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Term
What is a prophage?
What are lysogens?(lysogenic bacteria)
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Definition
-The form of a phage genome that remains within its host, that is often integrated into the host chromosome.
-The infected bacterial host.
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Term
What are lambda Phages characteristics? |
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Definition
• Icosahedral capsid (head) of 55nm in diameter
• A non-contractile tail with a thin tail fiber at the end
• double-stranded DNA phage
• A linear dsDNA genome of 48,502 bp
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Term
How is phase lamda DNA injected?
How many Base pairs does it have?
How does it lyctically replicate? What seals the breaks? |
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Definition
-Its linear dsDNA genome is injected into the host E. coli, and is circularized.
-The DNA contains 12 base single-stranded cohesive ends, cos sites. -Circularization results from complementary base pairing. The breaks are sealed by the host ligase. |
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Term
| What two proteins are key in a lambda phages cycle choice? |
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Definition
Two proteins play major roles in establishment of the lytic or lysogenic cycle: the lambda repressor and the Cro protein.
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Term
What does the Lambda repressor do and what is it gene?
What does the Cro protein do and what is its gene?
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Definition
-The lambda repressor is the product of cI gene. It blocks transcription of the cro gene and other genes required for the lytic cycle, but activates transcription of the cI gene, therefore enhancing its own synthesis.
-The Cro protein is encoded by the cro gene, and inhibits transcription of the lambda repressor gene. |
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Term
What happens if the Lambda protein wins the race? |
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Definition
The transcription of most viral genes (including cro) is blocked. This means that no viral DNA or viral structural proteins are made. More lambda repressor is then made to stabilize the lysogenic state.
• The lambda genome is then integrated into the host genome at the att site in a reaction catalyzed by the enzyme integrase. Integrase is encoded by the phage gene integrase.
• As a result of the Lamda protein winning lysogeny is established. |
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Term
| What happens if the Cro protein wins the race? |
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Definition
• If the Cro protein wins the race with lambda repressor, it blocks synthesis of lambda repressor and prevents integration of the lambda genome into the host chromosome. Phage proteins are then made and the phage DNA is replicated causing the lytic cycle to begin. |
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Term
| How can a phage get out of a lysogenic cylce? |
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Definition
The phase can get out of lysogeny by induction. This is triggered by a drop in the lambda repressor levels. As the lambda repressor levels decrease, xis, int and cro genes are transcribed. Excisionase binds to integrase and enables it to reverse the integration process. |
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Term
| What is lysogenic conversion? |
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Definition
• Lysogenic bacteria are immune to super infection. Changes in host phenotype caused by lysogeny are called lysogenic conversion. Changes in host phenotype caused by lysogeny
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Term
| What does Phage epsilon of Salmonella do? |
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Definition
Modify the Salmonella lipopolysaccharide structure, which is the receptor of the epsilon phage. |
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Term
What does Corynebacterium diphtheriae create during a lysogenic conversion? |
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Definition
Produces the diphtheria toxin. The diphtheria toxin is encoded by gene of phage b. |
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Term
Two phages that carry toxin and their gene products?
CTX phage?
Beta Phage? |
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Definition
Phage: CTZ
Gene:ctxAB
Gene product/phenotype:Cholrera toxin
Bacterial host:Vibrio cholera
Phage: Beta-Phage
Gene: tox
Gene product/phenotype:Dieptheria toxin
Bacterial host: Corynebacterium diptheriae |
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Term
| What is specilaized transduction? What cylce does it occur in? |
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Definition
Specialized transduction is carried out only by temperate phages that have established lysogeny.
-Only specific portion of bacterial genome is transferred. -It integrates into the host DNA and undergoes induction(trying to cut itself out of host cell)It ends up taking part phage DNA and part host.
-It occurs when the prophage is incorrectly excised.
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Term
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Definition
– Transduction is the transfer of bacterial genes by phages. Any part of bacterial genome can be transferred. A phage acquires a part of bacterial chromosome during lytic cycle, and brings it into the next bacterium. During viral assembly, fragments of host DNA are mistakenly packaged into phage head. |
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Term
| What does a Salmonella phage p22 have/do? |
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Definition
Salmonella phage P22 has an icosahedral head and a short tail. Like most dsDNA phages, it uses a phage-encoded enzyme called terminase to pack newly synthesized phage DNA into the pre-formed prohead. But the terminase can mistakenly package host DNA instead of phage DNA into the prohead. Such a phage particle (transducing particle) brings this piece of host DNA (donor DNA) to the next bacterium (recipient), therefore transfer genes from bacterium to bacterium. This is called generalized transduction. Generalized transduction doesn’t require lysogenic phages, and any part of the host DNA can be transduced. |
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Term
| what is the main difference between general and specialized transduction? |
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Definition
General: Fragment host DNA randomly. Only takes up host DNA.Occurs only during lyctic cycle.
Specilized:Interages into host DNA and undergoes induction. Takes up part phage and part host DNA. Only occcurs during lysogenic cylcle. |
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Term
| What is the life cylce of T4 phage (continued) |
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Definition
| After the lifecycle is complete, the host cell bursts open and ejects the newly built viruses into the environment, destroying the host cell. T4 has a burst size of approximately 300 viral particles per infected host. |
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