Micro chp. 5

Which of the following is not a type of viral nucleic acid? a. single-stranded DNA b. double-stranded RNA c. double-stranded DNA d. segmented RNA e. all of the above

e. all of the above

Bacteriophage

-"bacteria eating" -Most contain double-stranded DNA, but some RNA types exist as well -Every bacterial species is parasitized by various specific bacteriophages -Often make the bacteria they infect more pathogenic -ex: E. coli

Lysogeny

-A condition in which the host chromosome carries viral DNA

Virion

-A fully formed virus that is able to establish an infection in a host cell

Using bird embryos for inoculations

-Bird eggs containing embryos: they are intact and self-supporting unit, sterile environment, and contain their own nourishment -Chicken, duck, and turkey -Virus is injected through the eggshell by drilling a small hole or making a small window

Spikes

-Can be found on naked or enveloped viruses -Project from the nucleocapsid or the envelope -Allow viruses to dock w/ host cells

Persistent infections

-Cell harbor the virus and is not immediately lysed: can remain for a few weeks or the remainder of the host's life; can remain in the cytoplasm

Penetration and uncoating

-Cell membrane of host is penetrated by the whole virus or its nucleic acid -Penetration through endocytosis happens when an entire virus is engulfed by the cell and enclosed in a vacuole or vesicle -Uncoating: --enzymes in the vacuole dissolve the envelope and capsid --virus fuses w/ the wall of the vesicle --viral nucleic acid is released into the cytoplasm

Types of CPEs

-Changes in shape and size -Development of intracellular changes -Inclusion bodies: compacted passes of viruses or damaged cell organelles in the nucleus and cytoplasm -Syncytia: fusion of multiple host cells into single large cells containing multiple nucleus

Viral genes

-Contain DNA or RNA but not both -Number of genes is a lot smaller than a cell (4 genes in hep. B virus; hundreds in some herpesviruses) -Possess only the genes needed to invade host cells and redirect their activity

Synthesis

-DNA viruses: enter the host cell's nucleus and are replicated and assembled there -RNA viruses: replicated and assembled in the cytoplasm -Retrovirus turn their RNA genomes into DNA

Satellite viruses

-Dependent on other viruses for replication

Prions

-Deposited as long protein fibrils in the brain w/ no nucleic acid

RNA viruses

-Double-stranded, but more often single -Positive-sense RNA: ready of immediate translation -Negative-sense RNA: must be converted b4 translation can occur -Segmented -Retroviruses: carry their own enzymes to create DNA out of RNA

Substances in virus

-Enzymes for specific operations within host cell: --Polymerases - synthesize DNA and RNA --Replicases - copy RNA --Reverse transcriptase - synthesizes DNA from RNA -Completely lack the genes for synthesis of metabolic enzymes -Some viruses carry away substances from their host cell: retroviruses borrow the host's tRNA molecules

What does viruses infect?

-Every cell type including bacteria, algae, fungi, protozoa, plants, and animals -Louis Pasteur proposed the term virus

Viruses and cancer

-Experts estimate that 20% of cancers are caused by viruses -Transformation: the effect of oncogenic, or cancer-causing viruses - some viruses carry genes that directly cause cancer --other viruses produce proteins that induce a loss of growth regulation, leading to cancer

Envelope

-External covering of a nucleocapsid, usually a modified piece of the host's cell membrane

Spongiform encephalopathies

-Implicated in chronic, persistant diseases in humans and animals -Brain tissue removed from affected animals resembles a sponge -Long period of latency before first clinical signs appear

Transformed cells

-Increase rate of growth -Alterations in chromosomes -Changes in cell surface molecules -Capacity to divide indefinitely

The vital role of viruses in evolution

-Infect cells and influence their genetic makeup -Shape the way cells, tissues, bacteria, plants, and animals have evolved -10% of the human genome consists of sequences that come from viruses -10-20% of bacterial DNA contains viral sequences

Using cell (tissue) culture techniques

-Isolated animal cells are grown in vitro or tissue culture rather than in an animal or egg -Cell cultures: --Grown in sterile chambers w/ special media that contain the correct nutrients for cells to survive --Cells form a single confluent sheet of cells that supports viral multiplication --Allows for the close inspection of culture for signs of infection

Oncoviruses

-Mammalian viruses capable of initiation tumors -Papillomaviruses -Herpes virus -Hepatitis B -HTLV

Treatment of animal virus infections

-Most antiviral drugs block viral replication by targeting the function of the host cells, but w/ severe side effects -DRACO: causes virus-infected cells to destroy themselves -Vaccines are valuable, but there are a limited number available

Detection of viral growth in culture

-Observation of degeneration and lysis of infected cells -Plaques: areas where virus-infected cells have been destroyed and show up as a clear, well-defined patches in the cell sheet --Microscopic manifestation of cytopathic effects (CPEs) -This same technique is used to detect and count bacteriophages: --Plaques develop when grown in bacterial cell culture --Viruses released by an infected cell radiate out to adjacent host cells --New cells become infected, they die and release more viruses, and the process continues --Plaque manifests as a macroscopic, round, clear space that corresponds to areas of dead cells

Danger of lysogeny

-Occasionally phage genes in the bacterial chromosome cause the production of toxins or enzymes that cause pathology in the human -Lysogenic conversion: when a bacterium acquires a new trait from its temperate phage

Chronic latent state

-Periodically become activated under the influence of various stimuli -Herpes simplex and herpes zoster viruses

Capsid

-Protein shell that surrounds the nucleic acid -Nucleocapsid: the capsid together w/ the nucleic acid -Naked viruses consist of a nucleocapsid -Most prominent feature -Composed of identical protein subunits called capsomeres -Capsomeres spontaneously self-assemble into the finished capsid -2 different types: helical and icosahedral

DNA viruses

-Single-stranded (ss) -Double-stranded (ds) -Linear -Circular

Size of viruses

-Smallest infectious agents -Smallest viruses: parvoviruses around 20 nm in diameter -Largest: mimiviruses around 450 nm in length

Enveloped viruses

-Take a bit of the cell membrane when they are released from a host cell -Enveloped viruses can bud from: cell membrane, nuclear envelope, or ER

Release

-The number of viruses released by infected cells is variable, controlled by: size of the virus and health of the host cell

Filterable virus

-These early researchers found that fluids from host organisms passed through porcelain filters designed to trap bacteria, the nitrate remained infectious -This proved that a cell-free fluid contain agents that could cause infection

Temperate phages

-Undergo adsorption and penetration -Do not undergo replication or release immediately

Absorption

-Virus can invade its host cell only through making an exact fit w/ a specific host molecule -Cells that lack compatible virus receptors are resistant to absorption and invasion by that virus

Induction

-Virus in a lysogenic cell becomes activated and progresses directly into viral replication

Assembly

-Virus is put together using "parts" manufactured during the synthesis process

Cytopathic Effects (CPEs)

-Virus-induced damage to the cell that alters its microscopic appearance -Accumulated damage from a virus infection kills most cells

Viroids

-Virus-like agents that parasitize plants -About 1/10 the size of an average virus -Composed of naked strands of RNA, lacking a capsid or any other type of coating

Viral components

-Viruses bear no resemblance to cells and lack any of the protein-synthesizing machinery found in cells -Viral structure is composed of regular, repeating subunits that give rise to their crystalline appearance -The structure contains only those parts needed to invade and control a host cell: external coating, core containing one or more nucleic acid strains of DNA or RNA, and sometimes 1 or 2 enzymes

Provirus

-Viruses incorporate into the DNA of the host -Measles virus

Cultivating and identifying animals viruses

-Viruses require living cells as their "medium" -In vivo: laboratory-bred animals and embryonic bird tissues -In vitro: cell or tissue culture methods -Primary purposes of viral cultivation: --Isolate and identify viruses in clinical specimens --Prepare viruses for vaccines --Do detailed research on viral culture, multiplication cycles, genetics, and effects on host cells

Put the phases of the life cycle of animal viruses in the correct order. a. assembly b. penetration c. release d. adsorption e. synthesis f. uncoating

-adsorption -penetration -uncoating -synthesis -assembly -release

Obligate intracellular parasites

-cannot multiply unless they invade a specific host cell and instruct its genetic and metabolic machinery to make and release new viruses

Viral replication cycle

1. Absorption 2. Penetration and uncoating 3. Synthesis 4. Assembly 5. Release -Length of cycle varies from 8 hours to 36 hours

The viral debate

1. Since viruses are unable to replicate independently from the host cell, they are not living things and should be called infectious molecules 2. Even though viruses do not exhibit most of the life processes of cells, they can direct them, and this are certainly more than inert and lifeless molecules -Viruses are better described as active or inactive rather than alive or dead

Creutzfeldt-Jakob disease and Bovine spongiform encephalopathy are caused by prions. Which of the following best describes a prion? a. viral particle b. naked DNA c. infectious protein d. small bacterium e. naked RNA

c. infectious protein

Which of the following best describes viruses? a. heterotrophic b. saprobic c. obligate intracellular parasites d. chemoautotrophic e. photosynthetic

c. obligate intracellular parasites