Intro (Lectures 1-3) Flashcards
Which is true: (a) All viruses make us sick and can be lethal; (b) our immune system can manage most viral infections; (c) humans are usually infected with one virus at any given time; (d) the press is usually correct in their virology reporting; (e) our immune system cannot handle most viral infections?
TRUE: our immune system can manage most viral infections
Define “virus”
an infectious obligate intracellular parasite comprising of DNA or RNA surrounded by a protein coat and/or envelope
What are the 6 definitive properties of viruses?
small particles, infectious obligate intracellular parasites, RNA/DNA genome–> directs synthesis of viral proteins via host processes; virions are formed from pre-formed components; progeny virions are the vehicle for transmission
What type of microscopes can you see viruses with?
electron microscope
How many viruses are needed to go into one host cell to cause an infection
ONE
What are the 4 characteristics of virus classification?
nature of nucleic acid (DNA or RNA), symmetry of capsid (protein shell), presence/absence of lipid envelope, size
What are the 7 classes of viral genomes?
ssDNA, dsDNA, (+)ssRNA, (-)ssRNA, dsRNA, dsDNA w/RT, (+)ssRNA w/RT
Which viral genome is essentially mRNA?
(+)ssRNA
What is the ONE goal of all viruses?
to produce progeny by transcribing mRNA in-order to make their protein to start self-assembly as well as replicate their genome
What provides the answer as to what will be the first biosynthetic event a type of virus needs to accomplish once it gets into the host cell?
the Baltimore Classification Scheme
What causes viruses to evolve?
environmental pressures
What are the 4 characteristics that identify viruses as “non-living”?
cannot make their own building blocks (nucelic acids/amino acids; do not reproduce via cell divison; can’t metabolize or make ATP, relies on host-cell machinery/processes
What are the 2 stages/phases that viruses have?
Virion phase and Infected Cell phase
What is the Virion phase of a virus?
virus is outside host cell in an inert state just floating; only consists of protein coat/envelope and genome
What is the Infected Cell phase of a virus?
when virus is undergoing active production of new progeny by taking over the host cell turning it into a factory
How are viruses simple?
all they do is replicate and infect by using host cell processes; they are only active after they replicate in a cell
What are the 3 objectives of virology?
how viruses enter cells, how they replicate, how they assemble
What are the 3 states that host cells can be/are regarding viral infection and replication?
susceptible, resistant, permissive
What is a susceptible host cell?
cell has a functional receptor on its surface that is compatible to a virus that has the matching binding protein
What is a permissive host cell?
cell has the capacity to replicate virus
What is a resistant host cell?
cell has no receptor or cannot support viral replication
Can a cell be permissible and not susceptible or vice versa?
No it needs to be both in order to take up a virus and replicate it
What are 2 things the cell needs to be in order to be infected?
susceptible and permissive
What type of cells are less permissive to viruses?
mature cells
What do viruses need to carry out replication? What do they not have that they are going to use from the host cell?
ribosomes (protein translation machinery); genetic material replication enzymes (may come with its own); energy (ATP); basic building blocks (ie: nucleic acids and amino acids); and host cell’s transportation system (ie: actin and microtubules)
Where do RNA viruses need to replicate?
cytoplasm
When replicating the RNA, which enzyme do they need to use?
RNA-dependent RNA polymerase
Where do DNA viruses need to get their genome to?
the nucleus
When replicating the DNA, which enzyme do DNA viruses need to use?
DNA-dependent DNA polymerase
What are the cell’s mechanisms that the DNA virus will use in order to transport their genetic material into the nucleus?
G-protein and microtubules
Where do viral infections typically begin at? Which type of cells are these typically?
the surfaces of the body that are exposed to the environment; epithelial and endothelial cells
What are the sides of epithelial cells?
basolateral surface and apical surface
What is the basolateral surface of epithelial cells?
faces basement membrane
What is the apical surface of epithelial cells?
faces lumen or external environment
Which side of endothelial/epithelial cells do viruses generally attach to?
apical surfaces
What is the extracellular matrix?
provides mechanical support and holds cells and tissues of the body together
What are integrins?
proteins that link the basolateral membrane to ECM
What are cadherins?
proteins that hold together cells such as epithelial cells via tight junctions
What type of cells are normally detached?
cancerous cells
Why do cells generally need to be attached? What happens to them when they become detached?
Cells need to be attached so they can communicate signals to each other and maintain survival; if they detach, they will undergo apoptosis
What are some of the proteins that make up the ECM?
collagen and fibronectin
In which way do phospholipids move?
laterally
What is a distinct characteristic about phospholipids?
amphiphatic molecules that have a non-polar and a polar side
What are 2 types of membrane proteins?
integral membrane proteins and indirectly anchored proteins
What are integral membrane proteins?
can cross part of or the entire span of the lipid membrane
What are indirectly anchored proteins?
can be anchored onto the lipid membrane by a lipid molecule
What are the 7 steps in the Infectious Cycle?
Attachment | Penetration/Entry | Uncoating | Genome Expression/Replication | Assembly | Maturation | Egress/Exit
What is the “Attachment” step?
virus binds to cell surface receptor
What is the “Penetration/Entry” step?
virus breaks into cell by crossing plasma membrane (actin remodeling) and then needs to break out of endosome to get into cytoplasm
What is the “Uncoating” step?
virus gets rid of capsid and localizes its genome
What is the “Viral Gene Expression/Replication” step?
genome needs to be transcribed and translated to make viral proteins and then it needs to be replicated
What is the “Assembly” step?
newly synthesized viral proteins and replicated genome will then be assembled de novo
What does “de novo” mean in regards to viral assembly?
no proteins assisting the virus to get assembled (mostly occurs via signaling sequences)
What is the “Maturation” step?
proteins within newly assembled virus will undergo proteolytic cleavage to increase its stability
What are 2 ways viruses leave mammalian cells?
lysis or budding off/secretion
What are the 3 conclusions of the Burst concept?
one cell makes hundreds of progeny and each cell makes around the same number of viruses; the cell has a finite number of progeny produced per cell
What does “Burst” mean?
the progeny yield from one cell = one viral generation
