Lecture 18- Viruses Flashcards
virus
infectious particle consisting of genes packaged in a protein coat; sometimes may have an outer envelope or membrane; require host to replication (obligate, intracellular parasites)
origin of viruses
progressive, regressive, virus-first hypothesis
progressive/escape hypothesis
viruses arose from genetic elements that gained the ability to move between cells
regressive/reduction hypothesis
viruses are remnants of cellular organisms
virus-first hypothesis
viruses predate or coevolved with their current cellular hosts
characteristics of a virus
host, genome, capsid, envelope
viral genomes
DNA or RNA (double or single stranded), single linear or circular molecule of the nucleic acid
capsid
protein shell that encloses the viral genome, built from proteins capsomeres
viral envelopes
derived from host cell membranes, surround capsid of influenza viruses
bacteriophages/phages
elongated capsid head that encloses their DNA and a protein tail piece attaches the phage to the host and injects the phage DNA inside
host range
a limited number of species a virus can infect; broad or small;
central dogma an viruses
take advantage of central dogma
viral replication
- recognition of host cell and attachment, entry 2. genome replication and. protein synthesis 3. viral mRNA is produced and viral proteins are made using host ribosomes 4. assembly, new viral genomes associate with capsid proteins 5. release, mature virions leave the cell
lysogenic cycle
replicates the phage genome without destroying the host; viral DNA is incorporated into the host cell’s chromosome
temperate phage
phages that use both the lytic and lysogenic cycles; lambda
lytic cycle
a phage replicative cycle that culminates in the death of the host cell; produces new phages and lyses (breaks open host’s cell wall), releasing progeny viruses
virulent phage
a phage that reproduces oonly by the lytic cycle
classifying viruses that infect animals
an RNA or DNA genome, either single or double stranded, and the presence or absence of a membraneous envelope
retroviruses
use reverse transcriptase to copy their RNA genome into DNA (HIV); RNA polymerase transcribes the provirus DNA into RNA molecules for synthesis of viral proteins and release genomes for new virus particles
provirus
the viral DNA that is integrated into the host genome, PERMANENT resident of host cell
CRISPR-Cas system
prokaryotic defense, based on sequences called clustered regularly interspaced short palindromic repeats (make loop structure)
“spacer sequence”
corresponds to DNA from a phage that previously infected the cells
CRISPR-associated (cas) proteins
nuclease proteins that interact with the CRISPR region; use phage related RNA to target the invading phage DNA; phage DNA is cut and destroyed;
relationship between phage and bacteria
in constant evolutionary flux; natural selection favors phage mutants that can bind to altered cell surface receptors or that are resistant to enzymes
adaptive immune response
response to a specific pathogen; only present in vertebrates; recognizes very specific part of pathogen; produces antigen proteins
immune system
keeps the internal body free of disease causing microbes/pathogens in mammals
outside replicating pathogens
bacteria and fungi
inside replicating pathogen
viruses
3 major lines of defense
- barriers (physical, chemical, biological) 2. innate immune system 3. adaptive immune system
innate immune system
operates constantly, innate (skin, mucus membranes, enzymes, etc.); not affected by prior exposure, not directed specifically to a particular infectious agent
innate vs adaptive immunity
LOOOKKKK
pattern recognition receptors (PRRs)
present on host cells and recognize microbes; viral PRRs inside cell
pathogen-associated molecular patterns (PAMPs)
PRRs bind to these structures unique to mircobes and they signal immune response to pathogen, external or internal
PRR binds to PAMP
recognize PAMPs, produce cytokines to communicate infection to other cells
cytokines
diffuse to other cells and bind to cytokine receptors to transmit signal
anti-viral response
PAMP is intercellular
interferon response
PAMP is intracellular; interfere with infection, stop making new viruses, neighboring cells aren’t producing resources, gives innate immune cells an opportunity to respond, buys time
T cells and B cells
thymus and bone marrow; white blood cells adaptive immune system relies on; both bind to antigens via antigen receptors; remain dormant but infection is checked by 100s of them
pathogen specific
each individual B or T cell is specialized to recognize a specific type of molecule
epitopes
regions on the surface of antigens that have complementary shapes to antigen binding sites
colonial expansion
when a B or T cell is selected and starts to divide; creates army of clones to fight infection
plasmas cells
create and release antibody
memory cells
persist in body and wait for pathogen to enter again
immunological memory
responsible for long-term protections against diseases, due to prior infection or vaccination
primary immune response
first exposure to a specific antigen; selected B and T cells give rise to their effector forms
secondary immune response
memory cells facilitate a faster, more efficient response
