Module 2 Flashcards
difference between enveloped and non enveloped viruses
nonenveloped- have just a protein coat (capsid) surrounding their nucleic acid
enveloped- have a lipoid membrane consisting of lipids and carbohydrates (from hosts) and embedded viral proteins
a virus that infects bacteria is a
bacteriophage
steps of bacteriophage infection
Infection: binds and injects viral genetic material
replication of viral genetic information
production of viral proteins
assembly of viruses
lysis of bacterium
lytic vs lysogenic cycle
only for viruses that infect bacteria
lytic: always lyse
lysogenic: may or may not enter a lytic phase in the future, integrate their genomes into the host genome to be passed down
how do nonenveloped viruses infect a eukaryotic cell
bind to receptor to enter via endocytosis, where the capsid is degraded to release the viral genome
taken to nucleus to replicate, then leaves nucleus for assembly
released by lysis
their proteinaceous outer structure makes ___ viruses more tolerant to harsh conditions and disinfectants
nonenveloped
how does an enveloped virus infect a eukaryotic cell
attach via receptors to membrane, and since it can a lipid it fuses with the membrane and the virus is uncoated
genome replication (RNA to DNA in reverse transcription)
proteolytic processing: breaks large polypeptide into individual proteins to be functional
budding: viral particle encased in host membrane
what is a retrovirus
- Transcribe their RNA into DNA after entering a cell and then integrating into the chromosomal DNA of the host cell
describe the cell wall components of gram + bacteria
Structural but not barrier functions
Thick peptidoglycan layer (PG)
□ A polymer of alternating NAG and NAM (Glycan chain) that is bridged by short amino acid chains (Covalent cross links)
Teichoic and Lipoteichoic Acid
□ Help to maintain the entire cell envelope structure by anchoring the peptidoglycan layer to the cytoplasmic membrane
□ Net negative change to the cell wall and can be recognized during infections by the immune system
Size of Periplasmic space is smaller
describe the cell wall components of gram - bacteria
Thin PG layer
outer membrane: barrier function
large periplasmic space
outer membrane
-porins: protein channels
-lipoproteins: links PG to OM
-LPS: net negative charge, highly immunogenic
ways to cross the bacterial membrane
facilitated diffusion
-concentration graident
primary active transport
-low to high
-ATP
Secondary active transport
-movement of one molecule down CG lets other molecule move against its CG
Group translocation
-organic molecule (glucose) transported across membrane in conjunction with chemical modification
iron uptake
-strip iron off cell surfaces or use scavenger proteins (siderophores)
extracellular structures: capsules, slime and biofilms
Capsule
○ Layer of material firmly attached to an individual bacterium
Slime layer
○ Diffused, unorganized material that is easy to remove
- Offer protection by masking the bacteria from the immune system
Biofilm
○ Polysaccharides surrounding groups of bacteria
○ Heterogenous - contain different types of organisms
○ Important for bacterial colonization of both environmental and host surfaces
○ Get an environmental signal to do this
S-layer
-proteinaceous
flagella vs pili
flagella is movement in liquids
-basal body in cell membrane, hook and filament
pili is movement on solid surfaces via twitching
-thinner and shorter than flagella
-assembled on cell surface
archaeal wall types
s-layers
pseudomurein
simple
monolayer: very heat and chemical resistant, corresponds to unique habitats
how do bacterial biofilms contribute to virulence
protection from host defences
-immune evasion (physical barrier)
-antibiotic resistance (lessened penetration and HGT of resistant genes)
enhanced adhesion
-EPS help bind to surfaces including host tissue, leading to persistant infection
quorum sensing:
-coordinate expression of virulence factors based on population density, enhancing their pathogenicity
what are the two ways HIV attaches to the host cell
non-specifically with negatively charged proteins on the host cell surface
interation with the host cell surface: proteins bring the two membranes/surfaces together
-antiviral strategies target antibodies that recognize proteins suc has CD4
adenoviruses tend to infect what function of the host
respiratory
adenovirus binding
Spike on virus binds to CAR on membrane, then is endocytosed
-strong association occurs via irreversible binding of integrin to the base of the spike
vesicle is acidified and the virus is released into the cell
antigenic shift vs antigenic drift
Shift:
- Associated with large scale virus epidemics
- Occurs when there is a major change in the HA or NA antigens
- New strain
Drift
- Virus undergoes a gradual change in genetic makeup
- Similar genetic makeup to parent virus
how do pili enhance bacteria infection
‘sticky bits’ to bind bacteria to substrates, viruses use this as first step of infection
help form biofilms and shelter bacteria from immune system and target the cell
can elicit an immune response from the host
why is peptidoglycan structure an effective antimicrobial target
- It is unique to prokaryotes
○ So drugs less likely to be toxic to eukaryotes - Many pathogens have it, so it is an ubiquitous target
- Antibiotics targeting peptidoglycan do not need to cross the cytoplasmic membrane as the drug target is readily accessible
major difference between immune response to bacteria and to viruses
○ Viral infection is inside of host cell
○ Bacterial infection is extracellular
