Chapter 13
Defne viroids.
viroids: a naked (no capsid) infectious piece of RNA that lack nucleic acid and cause disease in plants viroidlike agents- infectious, pathogenic RNA particles that lack capsids but do not infect plants- affect some fungi.
Compare and contrast the release of viral partcles by lysis and budding.
budding: Enveloped viruses (e.g., HIV) typically are released from the host cell by budding. During this process the virus acquires its envelope, which is a modified piece of the host's plasma or other, internal membrane. -budding allows an infected cell to remain alive for some time Lysis: Viruses can be released from the host cell by lysis, a process that kills the cell by bursting its membrane and cell wall if present.
6. Discuss viral genomes in terms of dsDNA, ssDNA, ssRNA, dsRNA.
dsDNA= double stranded DNA; ssDNA=single stranded DNA; dsRNA= double stranded RNA; ssRNA= single stranded RNA • ssDNA and dsRNA are almost nonexistent in cells. • Prokaryotes and Eukaryotes the genome is primarily always DNA, whereas viral genomes are either DNA or RNA, never both. • Depending on the virus, the nucleic acid can be linear or circular.
Describe and explain transduction and explain its significance.
Bacterial genes can be picked up in a phage coat and transferred to another bacterium in a process called generalized transduction. Specialized transduction is mediated by a lysogenic phage, which packages bacterial DNA along with its own DNA in the same capsid.
1. Explain the general characteristics or viruses.
Originally called contagium vium fluidum, known as a contagious fluid. By 1930s called a virus, known as poison in Latin. Viruses are neither prokaryotic nor eukaryotic, and aren't considered living organisms (although it is still up for debate.) They are especially so small they can't be seen with a light microscope. Have few or no enzymes of their own for metabolism. • All viruses include 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. Considered intracellular parasites. • Cause the synthesis of specialize structures that can transfer the viral nucleic acid to other cells.
List different methods by which viruses enter the body.
You can eat them if they are in a certain type of food or live in the animal or plant you are eating. You can get them from the water, either swimming in it or drinking it. You can breath them in from the air and they enter your lungs or enter wounds
13. Explain viral taxonomy, and identify correct use of viral nomenclature.
Classification of viruses is bases on type of nucleic acid and strategy for replication. Nomenclature of a virus includes: Order, Family, Genus, Specific Epithet
Explain the 'H' amd 'N' in influenza Type A viruses, and functions of hemagglutinin and neuraminidase.
H=hemagglutinin; N= neuraminidase . Their main job is attaching viruses to a cell. Hemagglutinin is used to make anti-flu vaccines. There are 9 different types of neuraminidase. They are enzymes; neuraminidase release newly made viruses. Antiviral medications such a Tamiflu and Relenza inhibit this enzyme.
3. Explain the abundances of viruses.
It's almost impossible to wrap our heads around how many viruses exist among us. We have approximately 10^30 viruses in the ocean alone. The amount of viruses that exist extend 10^7 light years away (closest star is 4.2 light years away) and stretch farther than the nearest 60 galaxies.
Provide examples of a latent viral infecton in humans.
Latent viruses are those viruses that can incorporate their genetic material into the genetic material of the infected host cell. ... Examples of viruses include the Herpes Simplex Virus 1 (also dubbed HSV 1) and retroviruses .
Describe lysogeny in bacteriophages, and defne prophage, lysogenic conversion, and inducton.
Lysogeny, type of life cycle that takes place when a bacteriophage infects certain types of bacteria. In this process, the genome (the collection of genes in the nucleic acid core of a virus) of the bacteriophage stably integrates into the chromosome of the host bacterium and replicates in concert with it. - A prophage is the lysogenic viral DNA that is embedded in the host's DNA. -Induction is known as the lysogenic cycle converting into lytic cycle lysogenic conversion --> lysogeny. The ability of some phages to survive in a bacterium as a result of the integration of their dna into the host chromosome. The integrated dna is termed a prophage
Diferentate persistent viral infectons from latent viral infectons.
Persistent viral infection: Occurs gradually over a long period. Latent viral infection: virus remains in equilibrium with the host and not actually produce disease for a long period of time.
Identfy cancers known to be caused by viruses.
liver and cervical
Defne and describe prions, and the classifcaton of the human diseases they cause.
nfectious protein particles that lack nucleic acids prion PrP acts enzymatically to change the shape of cellular PrP (normal form) so that it becomes prion PrP (abnormal form). Prion PrP refolds cellular PrP into a prion shape. As ribosomes synthesize more cellular PrP, more prion PrP is converted. -Prion diseases are called spongiform encephalopathies and are associated with diseases such as: bovine spongiform encephalitis, chronic wasting disease in deer and elk, and Creutzfeld-Jacob disease in humans -no treatment for prion disease -prions are destroyed by incineration or by autoclaving in 1 normal NaOH
10. Differentiate among the different capsid shapes, and correctly classify if shown a picture or diagram
• Helical viruses= cylindrical capsid • Polyhedral viruses= icosahedron (regular polyhedron with 20 triangular faces and 12 corners) • Enveloped viruses=some capsids covered by an envelope. Enveloped viruses are roughly spherical. • Complex viruses=capsid head is polyhedral and that the tail sheath is helical
Explain why contact with viruses does not always lead to disease.
Viruses can be blocked by the skin; If viruses do pass through the skin into our system, they can be destroyed or inactivated when they enter the body. Some viruses can cause inapparent infection. Antibodies are made but no real symptoms are shown. And some dont infect humans
Compare and contrast prions, viroids, and viruses.
(Prions vs viruses) -Size: prions are smaller (5nm) vs. virus: 10-400nm -Nucleic acid: prions lack nucleic acid, but viruses contain DNA or RNA -protein: viruses lack protein, but prions have PrP -Self-replicating: virus cannot self-replicate, but prions can, transform PrP protein already present in cell -Responsiveness: some phages respond to a host cell by injecting their genomes, prions lack responsiveness (Viruses vs Viroids) -Viroids are similar to viruses in that they are infectious & contain single strand of RNA, however viroids lack proteinaceous capsid
Compare and contrast latency in animal viruses with phage lysogeny.
*Lysogenic Cycle: -Infected host cells grow and reproduce normally for many generations before they lyse. -A virus enters the cell in the same was as in the lytic cycle, but the bacterial DNA is not immediately degraded. -The virus remains inactive (prophage) -The prophage is inserted into the DNA of the bacterium, becoming a physical part of the bacterial chromosome (all daughter cells are infected) -The process whereby a prophage is excised from the host chromosome is called induction -After induction, the lytic steps of synthesis continue where they left off. *Lytic cell: -Viral DNA destroys cell DNA -Virions are released from lysed cell -Virulent viral infection takes place
Compare and contrast the replicaton of bacteriophages and of animal viruses.
--Attachment Sites Bacteriophage: Attachment of tail fibers to cell wall proteins Animal Virus: Attachment of spikes, capsid, or envelope to plasma membrane protein --Penetration Bacteriophage: Injection of viral nucleic acid through bacterial cell wall Animal Virus: Endocytosis or fusion --Uncoating Bacteriophage: none needed Animal Virus: Enzymatic digestion of viral proteins --Synthesis Bacteriophage: In cytoplasm. Bacterial synthesis ceased. Viral DNA or RNA replicated, formation of viral mRNA. Viral components synthesized. Animal Virus: In cytoplasm (RNA) or nucleus (DNA). Host cell synthesis ceased. Viral DNA or RNA replicated, formation of viral RNA. Viral components synthesized. --Maturation Bacteriophage: Addition of collar, sheath, base plate, and tail fibers to viral nucleic acid-containing head. Animal Virus: Insertion of viral nucleic acid into capsid --Release Bacteriophage: Host cell lysis Animal Virus: Budding (enveloped viruses), cell rupture (nonenveloped viruses) --Chronic infection Bacteriophage: Lysogeny Animal Viruses: Latency, chronic infection, cancer
Defne the terms neoplasia, tumor, benign, malignant, cancer, and metastasis
-There are two main classifications of tumors. One is known as benign and the other as malignant. A benign tumor is a tumor that does not invade its surrounding tissue or spread around the body. A malignant tumor is a tumor that may invade its surrounding tissue or spread around the body. A neoplasm is an abnormal growth of cells Cancer is the mutation of cells which cause abnormal cells and harm In metastasis, cancer cells break away from the original (primary) tumor, travel through the blood or lymph system, and form a new tumor in other organs or tissues of the body.
Describe the methods by which bacteriophages and animal viruses are cultured
-bacteriophages can be grown either in suspensions of bacteria in liquid media or in bacterial cultures on solid media -Some animal viruses can be cultivated in embryonated eggs. -Cell cultures are cells growing in culture media in the laboratory
Describe some ethical and practcal difcultes to overcome in culturing viruses.
-some practices use live animals -maintaining laboratory animals can be difficult & expensive. Growing viruses that infect only humans raises ethical concerns.
Describe the 5 stages of the lytic replication cycle as it typically occurs in bacteriophages.
1) Attachment- after a chance collision between phage particles and bacteria, attachment (or adsorption) occurs. During this process, an attachment site on the virus attaches to a complementary receptor site on the bacteria cell. 2) Penetration- After attachment, the T-even bacteriophage injects its DNA (nucleic acid) into the bacterium. To do this, the bacteriophage's tail releases an enzyme, phage lysozyme, which breaks down a portion of the bacteria cell wal The capsid remains outside the bacterial cell. Therefore the phage particle functions like a hypodermic syringe to inject its DNA into the bacterial cell. 3) Biosynthesis- the biosynthesis of viral nucleic acid and protein occurs. Initially, the phage uses the host cell's nucleotides and several of its enzymes to synthesize many copies of phage DNA. Soon after, the biosynthesis of viral proteins begins. 4) Maturation- In the next sequence of events, maturation occurs. In this process, bacteriophage DNA and capsids are assembled into complete virions. the head is filled with phage DNA and attached to the tail. 5) Release-The final stage of viral multiplication is the release of virions from the host cell. Lysozyme, which is encoded by a phage gene, is synthesized within the cell. This enzyme causes the bacterial cell wall to break down, and the newly produced bacteriophages are released from the host cell. The cell released bacteriophages infect other susceptible cells in the vicinity, and the viral multiplication cycle is repeated within those cells.
9. Describe the function of the capsid, and the capsomeres.
A capsid is a protein that protects the nucleic acid of a virus. Each capsid is composed of protein subunits called capsomeres. Function of a capsid is to protect the nucleic acid from digestion by enzymes and allow the virion to attach to a host cell. Capsomeres enable the virion to penetrate the host cell membrane and in some cases, to inject the infectious nucleic acid into the cell's cytoplasm.
Describe the structure and formation of the viral envelope, its spikes, and hemagglutination.
Depending on the virus, envelopes may or may not be covered by spikes, which are carbohydrate-protein complexes that project from the surface of the envelope. Some viruses attach to host cells by means of spikes. Spikes are such a reliable characteristic of some viruses that they can be used as a means of identification. The ability of certain viruses, such as the influenza virus, to clump red blood cells is associated with spikes. the viruses bind to red blood cells and form bridges between them. The resulting clumping is called hemagluttination and is the basis for several useful laboratory tests.
define the terms nonenveloped virion and enveloped virion.
Enveloped virus has the membranous envelope surrounding the capsid. The enveloped virus rarely does cell lysis in the host. Non-enveloped virus lacks such covering and has capsid as the outermost part. Enveloped virus are sensitive to the conditions like drying and heating Non-enveloped virus even remains effective after drying and provides resistance against the conditions like heating and drying. Enveloped virus gets the transmission to the living cells through the secretions, and most notably through blood or organ transplants. Non-enveloped virus gets the transmission to the living cells through the oral matter or fecal.
16. Describe what is meant by an inapparent infection.
Inapparent infection is the presence of infection in a host, They are asymptomatic or non-detectable; no noticeable illnesses.
Compare and contrast the lysogenic replicaton cycle of viruses with the lytc cycle.
Lytic cycle usually ends with the death and lysis of host cell; lysogenic can incorporate themselves into the host cell as a prophage and lie dormant until the conditions are right for it to release itself from the genome of the host cell.
14. List and explain the four different methods by which viruses are classified.
Nucleic Acid: • DNA or RNA (never both) • dsDNA, ssDNA, ssDNA, ssRNA Envelope or not: • Some capsids covered by an envelope. Enveloped viruses are roughly spherical. Capsid shapes: • Structure of capsid is determined by the viral nucleic acid and accounts for most of the mass of a virus, especially of small ones. Viral size: • Determined with the help of an electron microscope. Viruses can range from 20 to 1000 nm in length.
Explain how a cell may become cancerous, with special reference to the role of viruses and Describe oncogenes and their importance in cancer.
Protooncogens: genes that play a role in cell division, as long as these genes are repressed, no cancer results Oncogene: protoocogenes when they are active, inactivation of oncogene repressors can cause cancer to develop Environmental factors such as UV light, radiation, and carcinogens, and viruses cause cancer -some viruses carry copies of oncogenes as part of their genomes, some viruses promote oncogenes that is already present in host, and other viruses interfere w/normal tumor repression when they insert (as provirus) into repressor genes
Describe the replicaton of animal viruses, and defne uncoatng and budding.
The stages are: 1. Adsorption 2. Penetration 3. Un-Coating 4. Replication of Viral Genome 5. Synthesis and Assembly of Virus Capsids 6. Release of New Virus. -budding enables viruses to exit the host cell and is mostly used by enveloped viruses which must acquire a host-derived membrane enriched in viral proteins to form their external envelope uncoating is A process in which the viral capsid of a virus is removed, leading to the release of the viral genomic nucleic acid.
4. Compare and contrast bacteria and viruses.
Typical bacteria vs. viruses (Rickettsias/Chlamydias not included.) Bacteria are not have intracellular parasite, viruses are. Bacteria have plasma membrane and binary fission, viruses do not. Typical bacteria do not pass through bacteriological filters, whereas viruses do. Bacteria possess both DNA and RNA, ATP generating metabolism, ribosomes, and are sensitive to antibiotics; meanwhile, viruses do not. Bacteria are not sensitive to interferon, viruses are.
2. Explain why viruses require an electron microscope to visualize.
Viral sizes are determined with the aid of electron microscope. Vary considerably in size. Majority of viruses are substantially smaller than bacteria. Viruses range from 20 to 1000 nm in length.
Explain cell transformaton to tumor cells, and the three ways viruses can cause cell transformaton.
Viral transformation is the change in growth, phenotype, or indefinite reproduction of cells caused by the introduction of inheritable material. The growth of transformed cells can be impacted by a loss of growth limitation -introducing an oncogene into a cell -disrupting regulation of normal cell division -stimulating uncontrolled growth of tissue and damaging DNA
5. Define virion, capsid, nucleocapsid, virus, and envelope.
Virion- a complete, full developed, infectious viral particle surrounded by protein coat when outside the host cell Capsid- the protein coat protecting the nucleic acid of the virus Nucleocapsid- the capsid of a virus with the enclosed nucleic acid Virus- biological agent that reproduces inside the cells of living hosts Envelope- outermost layer (either a capsid or envelope) provides protection & recognition sites
7. Discuss what organisms viruses can infect, and the specificity of viruses.
Viruses can infect all organisms; even viruses can infect other viruses. There are persistent and latent viral infections. Persistent infections are characterized as those in which the virus is not cleared but remains in specific cells of infected individuals. When a virus is present in the body but exists in a resting (latent) state without producing more viruses. A latent viral infection usually does not cause any noticeable symptoms and can last a long period of time before becoming active and causing symptoms.
8. Compare the relative sizes of viruses, bacteria, and eukaryotic cells.
Viruses in most cases are substantially smaller than bacteria. Eukaryotic cells are generally much larger than prokaryotic cells due to the materials they have inside the cell. From smallest to largest in size: viruses, bacteria, and eukaryotic cells.