Lecture 19 - Viruses Flashcards
What are the 7 characteristics of life?
- metabolism
- reproduction
- cellular organization
- homeostasis
- growth
- adaptation
- response to stimuli
Do viruses have metabolisms? Can they reproduce?
only with help from host cell
Do viruses have cellular organization?
no cells, no nuclei, no organelles, no cytoplasm
Do viruses have homeostasis?
- generally no
- no cells/cellular components in which to maintain an internal environment
Do viruses have growth?
no. built by host cell in fully-formed state
Do viruses adapt?
yes, evolutionary change over time in response to selection
Do viruses have a response to stimuli?
don’t response to touch/sound/light but they can be impaired/killed by antivirals
What are the 4 steps of the experiment done with tobacco and sap?
- extracted sap from tobacco plant with tobacco mosaic disease
- passed sap through porcelain filter
- rubbed filtered sap on healthy tobacco plants
- healthy plants became infected
What are viruses?
- not cells
- infectious particles consisting of nucleic acids in a protein shell
- sometimes in a membranous envelop
What is a capsid?
protein shell
What are possible hosts for a virus?
-archaea, plants, animals, fungi, protists
What are possibilities for the genome?
- linear or circular
- one piece or mutliple pieces
- RNA or DNA
- double or single stranded
What are 4 major viral groups?
…
What is a large virus?
pandoravirus
How does replication of viruses work?
- only in host cells
- most use of host’s enzymes, ribosomes, tRNA, amino acids, ATP and other molecules
What are 2 ways that the phage can reproduce?
- lytic cycle
- lysogenic cycle
What is the lytic cycle?
- virus attach to bacteria
- inject phage DNA + degrade host DNA
- synthesize viral genomes/proteins
- self-assembly of viruses
- release viruses (destroy host)
What is the lysogenic cycle?
- virus attach to bacteria
- inject phage DNA
- integrate into host DNA
- prophage copied with bacterial chromosome
- many divisions create many infected bacteria
How do animal viruses reproduce?
often involving a viral envelop
What is a viral envelope?
-outer membrane
-Protruding
from the outer surface of this envelope are viral glycoproteins
-bind to specific receptor molecules on the surface of a host cell
What is a virulent phage?
A phage that replicates only by a lytic cycle.
What are the 5 steps to phage assembly?
- attachment
- entry of phage DNA and degradation of host DNA
- synthesis of viral genomes + proteins
- self-assembly
- release
What is a temperate phage?
-lytic and lysogenic cycles of phage lambda
What is reverse transcriptase?
- transcribes an RNA template into DNA,
- providing an RNA S DNA information flow,
- the opposite of the usual direction.
- source of the word retro
What is a provirus?
The integrated viral DNA
What is herpes simplex type I
oral, cold sores
What is herpes simplex type 2
genital
What is herpes zoster
chickenpox/shingles
What are 4 types of host ranges?
- broad range (EX West Nile)
- species-specific (EX Measles)
- tissue specific (EX human cold)
What can recombinant viruses do?
expand host range
What are viroids?
- sub-viral pathogens
- circular RNA molecules without protein coats
- mostly infect plants
What are prions?
- infection proteins
- cause brain diseases include scrapie in sheep, mad cow disease, Alzheimer’s
What is the origin of viruses?
-hard to discern due to horizontal gene transfer + lack of fossil record
What is a viral shunt?
viruses move more nutrients (and carbon) from other organisms into particulate/dissolved pool
Why is HIV hard to treat/
-reverse transcriptase has hight mutation rate
What happens when immunity cells are attacked?
T4 helper cells arrive to scene
What is the conclusion from the tobacco experiment?
pathogen(virus) is smaller than bacteria
