| Are viruses living things? | Viruses are not living things, cells, because they cannot divide even if they were supplied with necessary nutrients, because of lack of metabolic enzymes for growth and division. |
| How are viruses present usually? | associated with cells and live by exploiting them. |
| Give some viral deseases. | AIDS, smallpox, chickenpox hepatitis, influenza, common cold, some cause cancer. |
| Describe generally viruses. | Small but diverse in terms of size(between 20-200 nm) shape and organization.
Nearly all viruses consist of one or more nucleic acid chains (DNA or RNA ss or ds, circular or linear) assembled with very few proteins such as polymerases and integrases, enveloped by a capsid of proteins. |
| Talk about the nucleocapsids. | used to describe nucleic acid of the virus, with the combined proteins, some have envelopes of lipid bilayer, others have a complex tail, some have naked nucleic acids called viroids, without any asssociated proteins, RNA of viroid is 50 nm length. |
| Why are viruses not living things? | they don't contain enzymatic equipment necessary for ribosome reproduction, oxidation, energy production, so they need a host cell to grow and multiply even smallest cells can be infected by a virus (mycoplasma) |
| What do viruses do to their host cells? | they are parasitic, deviate cell metabolism to their own benefit, exploit the cell. |
| Is viral infection specific? | specific, limited host cell infecting range, they are species-specific and organ-specific (lungs-COVID), tissue-specific (epithelia) and even cell or sub-cell specific.(HIV only infects T4-lymphocytes) |
| Why are viruses specific? | requirments of receptor of host cell, which mediated viral entry.but it is not absolute, (influenza can switch among species that they recognize their receptors. (COVID) |
| Talk about viral change. | Changes might occur to viruses, as they enter and leave the host cells, for instance influenza (A,B and C) at different strains, and modify each year, H-->hemaglutinin N-->neuraminidase. (H1N1 type 1 hemaglutinin type 1 neuraminidase) H and N are antigens at viral envelope. |
| Talk about the nucleic acids of the viruses. | may be DNA or RNA, encode for tens of protein types including capsid, polymerases necessary for their replication. |
| WTalk about the viral capsid. | Results from polymerization of many proteins (quaternary protein) may be enveloped by a lipid bilayer, (HIV influenza, smallpox.) determines viral shape |
| What are they main shapes of viruses? | rod Tobacco MV, globular, spherical (HIV), polyhedral (adenovirus) helical or filamentous some have a tail like structure and polyhedral, tails consist of sheath proteins in helical arrangement, specialized appandages may be found for attachment to receptors |
| What are the criteria of classification of viruses? | size, shape, symmetry, presence of lipid bilayer, nature of nucleic acids, infected cell host (bacteriophages prokaryotes viruses eukaryotes) |
| Give some examples of virus families. | -retroviruses (HIV- RNA)
-Orthomyxoviruses ( Influenza- RNA)
-Adenoviruses (Diseases on respiratory system and eyes- DNA) |
| Talk in general about the proliferation process of viruses. | Recognition of capsid or membrane to receptors of host cells, adhering to host surface and nucleic acid injection, which chooses either lytic or lysogenic circulation, hundreds of virses are produced in host which eventually dies. |
| How is virus-cell adhesion occuring? | viral proteins belonging to capsid or lipid bilayer, receptors of host cells adhere, ( CD4 (receptor protein of T4) -HIV glycoprotein/ Hemaglutinin mediates recognition of glycophorinn A of respiratory epithelium.) |
| How does viral injection occur? | Viral nucleic acids holds information required for viral reproduction, once virus reaches host cell, it injects its nucleic acids into cytoplasm, in case there is lipid bilayer envelope, fusion between cell membrane and viral membrane releases capsid in the cytoplasm which then dissociates to deliver NA, if no bilayer capsid is kept outside and NA are injected through a specific channel. |
| What is the third step of viral proliferation/ infection of the cell? | either lysogenic or lytic cycle, if RNA can be retrotranscribed (retroviruses) by reverse transcriptase, DNA genomes named proviruses happen, if no retrotranscription replicases (RNA dependant RNA polymerease) replicates RNA of virus. |
| How does the virus choose which cycle it will go through? | viral proteins or host cell conditions |
| Talk about lysogenic cycle. | viral DNA integrates with hosts chromosome via recombination, catalyzed by integrase, host cell is called lysogenic if viral DNA is integrated, silent, cells seems normal and lives normally, with cell division, silent lysogenic cells are produced, which may then become lytic (Surroundng signals UV radiation or stay silent. |
| Talk about the lytic cycle. | viral proteins mediate metabolism in favor of viral genome. (translation into capsids), which then produces new viral particles in the lysogenic cell, that metabolize and form a cage on nucleic acids. |
| What is the fifth step of virus proliferation? | Release of newly produced products, devoid of lipid envelope released by destruction of host cell envelope by enzymes produced by virus causing cell lysis. Those with a lipid bilayer bud from host cell surface, during formation of capsid, some proteins are synthesized necessary for exportation of viruses outside host plasma membrane, interaction between viral membrane proteins and capsids causes enveloping by a membrane fragment forming a bud for exprotation, for then the cell dies because of disturbed metabolism. |
| What are prions? | unusual pathogens, consist only of proteins, do not have nucleic acids like other pathogens, protease resistant, has an abnormal conformation, trasmitted to other copies of proteins, accumelate in cell causing toxicity by inferring with intracellular functions (transport, membrane polarity signal..) |
| Give examples on prions. | Transmissible spingoform encephalopathies (TSE) are prions caused diseases for animals, characterized by fatal neurodegeneration (encephalo=brain) scrapie in sheep, bovin was discovered 20th century.) Creutzfeldt-Jacob disease caused by eating BSE-infected food by humans. |
