Lecture 6 Flashcards
Viruses and Viroids (25 cards)
Define virus and virion, and describe the parts of a virion.
Virus: Acellular, protein coated, non-living, infectious agent having either DNA or RNA, never both. Can have envelope or be naked.
Virion: Extracellular state of a virus
Virion consists of a protein coat made up of capsomeres (variety of proteins) protecting the genetic material on the inside.
Discuss viral genomes in terms of dsDNA, ssDNA, ssRNA, dsRNA
dsDNA: double stranded DNA, found in all living cells, viral replication is similar to DNA replication, genome is made in the nucleus, proteins are made in the cytoplasm (ribosomes)
ssDNA: Cells do NOT use ssDNA, parvoviruses ssDNA strands fold back on themselves to form dsDNA which is then replicated by cellular DNA polymerase, newly replicated strand is released as ssDNA
dsRNA: RNA-Dependent RNA polymerase splits the dsRNA and transcribes the -ssRNA to +mRNA to a viral protein. Then, it copies +ssRNA and -ssRNA to make another copy of dsRNA
+ssRNA: can be translated directly to viral protein, RNA dependent RNA polymerase copies the +ssRNA strand to make a complimentary -ssRNA. The -ssRNA is then used to make +ssRNA
-ssRNA: cannot be directly translated to viral protein, it transcribes to +mRNA and +ssRNA. The +mRNA is then used to make proteins while the +ssRNA is used to make more copies of -ssRNA using RNA Dependent RNA polymerase.
Explain the mechanism by which viruses are specific for their host cells
Viruses are specific for their host cells because viruses attack specific cells of multicellular organisms and they bind to specific proteins that are located outside the cell. They have to attach to complimentary protein or glycoproteins located on the surface of the cell.
Compare and contrast viruses of fungi, plants, animals, and bacteria
Fungi: scientists do not know much about viruses in fungi. Their cell walls are too thick to be penetrated. Because fusing cells is part of the fungi life cycle, viral infections can be through fusion of an infected fungal cell.
Plants: Introduced into plant cells through abrasions of the cell wall or by plant parasites.
Animal: Animal viruses usually have an envelope to prevent detection of the host. They are inserted by direct penetration, endocytosis, or fusion. After the virus is inside the cell, it removes its capsids by cell enzymes. They have latent viruses and can be released through lysis and budding.
Bacteriophages: Proteins on tails attach to proteins on cell wall, its genome is injected to the cell or diffuses into the cell. the only release method is through lysis and it can go through lysogeny.
Discuss the structure and function of the viral capsid
The viral capsid is consisted of proteinaceous units called capsomeres composed of one or more protein. Nucleic acid surrounded by capsid is called nucleocapsid.
Discuss the origin, structure, and function of the viral envelope.
The viral envelope is only found in animal viruses through budding. The viral genome sometimes codes glycoproteins that send signals for the virus to bud out. The matrix proteins are what fills the region between the capsid and the envelope. This envelope helps with host recognition and prevents the virus from drying.
List the characteristics by which viruses are classified
Envelope, shape, type of nucleic acid
Sketch and describe the five stages of the lytic replication cycle as it typically occurs in bacteriophages
attachment, the virus attaches to the host’s tail fibers.
entry, the virus penetrates the cell wall using a protein enzyme called lysozyme that weakens the peptidoglycan wall. Then injects the cell with their nucleic acid.
synthesis, bacterium loses its chromosomes and stops synthesizing its own molecules and begins synthesizing viral proteins including lysozyme which weakens the cell wall allowing the virus to leave the cell wall once they have been assembled.
assembly, we do not know how phages are assembled inside the host cell
release, they are released once the cell wall disintegrates
Compare and contrast the lysogenic replication cycle of viruses with the lytic cycle.
the lysogenic cycle includes the virus fully integrating itself onto the bacteria’s nucleic acids and remain dormant where they’re replicated for generations. Induction is when chemical reactions trigger the viral genomes to act and then it goes through the lytic cycle.
Explain the differences between bacteriophage replication and animal viral replication
Attachment: Bacteriophages attach to bacterial cell walls, while animal viruses attach to host cell membranes.
Entry: Bacteriophages inject their DNA into the host, whereas animal viruses enter via endocytosis or membrane fusion.
Uncoating: Only animal viruses uncoat (removal of capsid); bacteriophages do not.
Replication: Bacteriophages replicate in the cytoplasm; animal viruses replicate in the nucleus (DNA viruses) or cytoplasm (+RNA, -RNA).
Release: Bacteriophages lyse the host cell; animal viruses release by budding (enveloped) or lysis (non-enveloped).
Compare and contrast the replication and synthesis of DNA, -RNA, and +RNA viruses.
DNA viruses: Replicate in the nucleus using host DNA polymerase.
+RNA viruses: Replicate in the cytoplasm; act as mRNA and are directly translated.
-RNA viruses: Need RNA-dependent RNA polymerase to make +RNA before translation.
Compare and contrast the release of viral particles by lysis and budding
Lysis: The virus breaks the host cell open, releasing virions. Common in non-enveloped viruses.
Budding: The virus pushes through the host membrane, acquiring an envelope. Common in enveloped viruses.
Compare and contrast latency in animal viruses with phage lysogeny
Latency (Animal Viruses): Virus remains dormant in host cells (herpes, HIV). It may reactivate later.
Lysogeny (Bacteriophages): Phage DNA integrates into bacterial DNA as a prophage and replicates with the host until induction occurs.
Define the terms neoplasia, tumor, benign, malignant, cancer, and metastasis.
Neoplasia: Uncontrolled cell division.
Tumor: A mass of abnormal cells.
Benign: Non-spreading, non-invasive tumor.
Malignant: Spreads and invades other tissues.
Cancer: Malignant tumor with uncontrolled growth.
Metastasis: Spread of cancer cells to distant body parts.
Explain in simple terms how a cell may become cancerous, with special reference to the role of viruses
Viruses can insert oncogenes or disrupt tumor suppressor genes, leading to uncontrolled cell growth. Examples: HPV causes cervical cancer, Epstein-Barr virus contributes to lymphoma.
Describe some ethical and practical difficulties to overcome in culturing viruses
Ethical: Use of live animals or human cells.
Practical: Viruses need a host to grow, contamination risks, expensive culture techniques.
Describe three types of media used for culturing viruses.
Cell cultures (monolayers of cells).
Embryonated eggs (used for vaccines).
Bacterial Culture
Explain the use of a plaque assay in culturing viruses in bacteria.
Used to count bacteriophages. Viruses lyse bacteria, forming clear zones (plaques) in a bacterial lawn.
List three problems with growing viruses in animals.
Ethical concerns.
Expensive and time-consuming.
They aren’t cultured how cells usually are cultured
Discuss aspects of viral replication that are lifelike and nonlifelike
Lifelike: Contain genetic material, evolve, replicate inside a host.
Non-lifelike: Cannot reproduce independently, lack metabolism, not made of cells.
Define and describe viroids.
Infectious RNA molecules that cause plant diseases.
Lack a capsid or proteins.
Compare and contrast viroids and viruses.
Viroids: Small, circular RNA, no proteins, only infect plants.
Viruses: Have DNA or RNA, protein coat, infect various organisms.
Define and describe prions, including their replication process, and contrast them with viruses.
Prions: Infectious misfolded proteins that cause neurodegenerative diseases.
Replication: Convert normal proteins into misfolded forms, leading to accumulation and brain damage.
Difference from viruses: No genetic material, cannot be inactivated like viruses.
Describe methods to control and destroy prions.
Autoclaving at high temperatures + chemicals (NaOH, bleach).
Incineration.
Enzyme-based treatments (Prion-degrading enzymes).
