Micro Lecture CH13
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Differentiate a virus from a bacterium
- Viruses and certain smal bacteria such as some rickettsias are very much alike:
- they both are intracellular parasites (while a typical bacteria is not)
- some rickettsias can pass thru bacteriological filters (while a typical bacteria cannot)
- other then that, typical bacteria and viruses are very different:
- typical bacteria: (these are things viruses cannot do/do not have)
- have a plasma membrane
- can binary fission
- possess both DNA and RNA (viruses have one or the other, never both)
- ATP-generating metabolism
- have ribosomes
- are sensitive to antibiotics
Viruses are sensitive to interferon while bacteria are not
Describe the chemical composition and physical structure of an enveloped and a nonenveloped virus.
- chemical composition-the envelope usually consists of some combination of lipids, proteins, and carbohydrates; some animcal viruses are released from the host cell by an extrusion process that coats the virus with a layer of the host cell's plasma membrane; that layer becomes the viral envelope. in many cases, the envelope contains proteins determined by the viral nucleic acid and materials derived from normal host cell components
- physical structure-depending on the virus, envelopes may or may not be covered by spikes; enveloped viruses are roughly spherical
- chemical composition-just has a protein coat over it called a capsid
- from powerpoint:
- The protein coatsurrounding the nucleic acid of a virus is called the capsid.
The capsid is composed of subunits, capsomeres, which can be a single type of protein or several types.
The capsid of some viruses is enclosed by an envelope consisting of lipids, proteins, and carbohydrates.
Some envelopes are covered with carbohydrate-protein complexes called spikes.
Define viral species.
A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species.
Give an example of a family, genus, and common name for a virus.
- ▫Coronaviridae (Family)
- ▫Coronavirus (Genus)
- ▫Common cold virus (Species) (together with rhinoviruses)
- ▫non-seg., lin., ssRNA, helical, env.
- corona-like (halo) appearance in electron micrographs.
- The corona or halo is due to an array of surface projections on the viral envelope, one of which is the E2 glycoprotein, the viral attachment protein and target of neutralizing antibodies.
- ▫Herpesviridae (Family)
- ▫Herpesvirus (Genus)
- ▫Herpes simplex type 1/ type 2 (Species)
- ▫non-seg., lin., dsDNA, helical, env.
Describe how bacteriophages are cultured.
- bacteriophages can be grown either in suspensions of bacteria in liquid media or in bacterial cultures on solid media
- the use of solid media makes possible the plaque method for detecting and counting viruses
- Growing Bacteriophages in the Laboratory
- The plaque method mixes bacteriophages with host bacteria and nutrient agar.
- After several viral multiplication cycles, the bacteria in the area surrounding the original virus are destroyed; the area of lysis is called a plaque.
- Each plaque originates with a single viral particle; the concentration of viruses is given as plaque-forming units.
Describe how animal viruses are cultured.
- Growing Animal Viruses in the Laboratory
- Cultivation of some animal viruses requires whole animals.
- Simian AIDS and feline AIDS provide models for studying human AIDS.
- Some animal viruses can be cultivated in embryonated eggs.
- Cell cultures are cells growing in culture media in the laboratory.
List three techniques that are used to identify viruses.
- Serological methods, such as Western blotting, are the most commonly used means
- also used are
- RFLPs (restriction fragment length polymorphisms)
- PCR (polymerase chain reaction)
Describe the lytic cycle of T-even bacteriophages.
- Phage attaches by tail fibers to host cell.
- Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell.
- Production of phage DNA and proteins.
- Assembly of phage particles.
- Phage lysozyme breaks cell wall.
Describe the lysogenic cycle of bacteriophage lambda.
- in contrast to t-even bacteriophages, some viruses do not cause lysis and death of the host cell when they multiply (lysogenic cycle)
- 1. penetration
- 2. the originally linear phage of DNA forms a circle
- 3a. this circle can multiply and be transcribed
- 4a. leading to the production of new phage and to cell lysis (the lytic cycle)
- 3. alternatively, the circle can recombine with and become part of the circular bacterial DNA (the lysogenic cycle). The inserted phage DNA is now called a prophage. Most of the prophage genes are repressed by two repressor proteins that are the products of phage genes.
- Everytime the host cell's machinery repliates the bacterial chromosome,
- 4b. it also replicates the prophage DNA. The prophage remains laten within the progeny cells
- 5. however a rare spontaneous even, or the action of UV light or certain chemicals, can lead to the excision (popping-out) of the phage DNA, and to initiation of the lytic cycle
Compare and contrast the multiplication cycle of DNA- and RNA-containing animal viruses.
- DNA, single stranded
- virus family: Parvoviridae
- Special features of biosynthesis: cellular enzyme transcribes viral DNA in nucleus
- DNA, double stranded
- virus family: Herpesviridae, Papovaviridae, Poxviridae
- Special features of biosynthesis: Herpesviridae-cellular enzyme transcribes viral DNA in nucleus; Poxviridae-Viral enzyme transcribes viral DNA in virion, in cytoplasm
- DNA, reverse transcriptase
- virus family: Hepadnaviridae
- Special features of biosynthesis: cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA
- RNA, + strand
- virus family: Picornaviridae, Togaviridae
- Special features of biosynthesis: Viral RNA functions as a template for synthesis of RNA polymerase which copies-strand RNA to make mRNA in cytoplasm
- RNA, - strand
- virus family: Rhabdoviridae
- Special features of biosynthesis: Viral enzyme copies viral RNA to make mRNA in cytoplasm
- RNA, double stranded
- virus family: Reoviridae
- Special features of biosynthesis: Viral enzyme copies - strand RNA to make mRNA in cytoplasm
- RNA, reverse stranded
- virus family: Retroviridae
- Special features of biosynthesis: Viral enzyme copies viral RNA to make DNA in cytoplasm; DNA moves to nucleus
Define oncogene and transformed cell.
Provide an example of a latent viral infection.
Differentiate between persistent viral infections and latent viral infections.
Discuss how a protein can be infectious.
Differentiate virus, viroid, and prion.
- -contain a single type of nucleic acid, either DNA or RNA
- -contain a protein coat (sometimes itself enclosed by an envelope of
- lipids, proteins and carbohydrates) that surrounds the nucleic acid
- -multiply inside living cells by using the synthesizing machinery of the cell
- -cause the synthesis of specialized structures that can transfer the viral nucleic acid to other cells
obligate intracellular parasite
absolutely require living host cell sin order to multiply
persistent viral infection
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