intro to viruses pt 1
structure and polarity RNA dependent RNA polymerase
RNA _____ and _____ determine how viral mRNA is generated ad proteins are processed. RNA viruses must carry _____ to replicate
labile and transient cytoplasm RNA dependent RNA polymerase
RNA is _____ and _____. most RNA viruses replicate in the _____. host cell cannot replicate RNA, so the virus must encode for _____.
positive or negative sense
RNA viruses can be considered _____ and _____
labile -temperature, pH, proteases, detergents, drying -detergents can open the lipid membrane
enveloped viruses are considered _____ and are disrupted by _____ (5)
lipid bilayer stolen from the host
enveloped viruses contain nucleic acids and capsid proteins surrounded by a _____
glycoprotein lipoproteins
enveloped viruses have viral _____ or _____ in the envelope for host recognition and entry
attachment flexible and coiled
envelopes of viruses are studded with viral _____ proteins. the nucleocapsid inside the envelope is _____ and _____
sialic acid o epithelial cells for influenza A attachment and recognition (hemaglutinin binds to it)
example of cell surface macromolecules used for host viral receptors
5 protomers come together to make a pentamer (capsomere). 12 capsomeres come together to form a mature virion
explain the assembly of a icosahedral virion with 12 pentamers
3 sialic acid subtypes
the influenza A hemaglutinin spike is composed of _____ functional spike proteins. altering any of these proteins alters its recognition and infectivity. this glycoproteins binds to epithelial cell _____ for infectivity. they are important immunological targets for virus serotyping as the specific hemaglutinin sequence identifies the viral _____
nucleic acid fluid enzymes
there is _____, _____, and _____ inside the icosahedral
-animal virus (humans, birds) -bacteria viruses (phage) (more complicated structure)
2 different types of host cells and how do their structures differ
DNA or RNA
the genetic material, or nucleic acid, of nucleocapsids are _____ and _____
capsomere assembly
the _____ structure and _____ predict the shape of the icosahedral
-icosahedral: nucleic acid and enzymes housed within a closed capsid -helical: nucleic acid wrapped around and with structural and enzymatic proteins
2 different types of structural protein coats (capsid)
-intrinsic capsid structure or surface proteins: grooves -envelope: glycoprotein spikes
2 ways host cells recognize viruses (VAP)
-endocytosis for naked viruses and some enveloped viruses -membrane fusion of only enveloped viruses (because of lips envelope)
2 ways in which viruses can penetrate into the host cell for viral replication cycle
-structure -biochemical characteristics: structure and mode of replication
2 ways to primarily classify viruses based on taxonomy
single chain multimeric segmented
3 different structure of DNA or RNA in viruses
-virus has DNA or RNA -structural proteins -enzymes and nucleic acids to make binding proteins
3 things that add up to a nucleocapsid on a virus
-lytic: blowing up and killing the cell to leave. (always naked viruses) -budding: leave a few at a time in membrane allowing host cell to live (envelope viruses can leave this way) -exocytosis: exported in a vesicle so host cell lives
3 ways a virus can be released from a host cell
-must stay wet -spreads in large droplets, body fluids, and organ transplants -may survive the digestive system (but many do not) -does not need to kill cell to spread (can stay behind and cause reinfection)
4 consequences of enveloped viruses
-easily spread on fomites, hand to hand (because more resistant) -can dry out and retain infectivity -can survive the digestive system -can survive poor sewage treatment
4 consequences of naked capsids
-B-cell complement receptors (CD21): Epstein Barr virus -T-cell CDA: HIV (HIV binds to CD4) -ICAM-1 on epithelial cells for rhinoviruses (common cold) -the neural cell adhesion molecules (NCAM/CD56) neuron on acetylcholine receptors for rabies virus.
4 examples of viruses using host cell surface integral membrane proteins as their viral receptors
-disease presentation -means of transmission -host cell (host range) -tissue or organ targets (tropism)
4 ways to secondarily classify viruses
-recognition of target cell -attachment (adsorption): sticking to -penetration: breaking through -uncoating: unpacking and taking over (unpack virus in host cell) -macromolecular synthesis: making new (protein synthesis and genome replication) -assembly and release: packing up and moving out
6 steps to the viral infection cycle
stabile transient and labile
DNA is more _____ and is NOT _____ or _____ like RNA
encephalitis and hepatitis
Disease presentations: _____ and _____ are each caused by multiple types of viruses
protomer
_____ are the individual capsid protein unites that are intimately associated with the genome
complex
_____ capsids have multiple subunits with specialized shapes and functions. -ex: bacteriophages
helical
_____ is a capsid composed of nucleic acids bound to protomers (proteins) in a spiral with a hollow phase inside
capsid
_____ is the grouping of structural proteins that surround and encase the viral genome
caps-mere
_____ is the individual structural protein subunits of a capsid -like the individual protein panels of icosahedral
envelope
_____ is the lipid membrane surrounding the nucleocapsid
tropism epithelium (nasopharyngeal, respiratory, intestinal)
_____ is the target organ or tissue a virus is infecting. viruses are only infectious for certain cells and a vast majority of viruses enter through _____
genome positive negative
_____ structure of RNA viruses determines the mechanism of transcription and replication. _____ RNA viruses act as mRNA and translate immediately. _____ RNA viruses must be copied to mRNA first
genome
_____ type heavily dictates the replication cycle of the virus
-DNA or RNA, rarely both -single or double stranded
a viruses genome can either be _____ or _____. then the can either be _____ or _____
negative
all _____ RNA viruses are enveloped
helical
all _____ viruses have are enveloped
envelope
all human helical viruses have an _____
nucleocapsid
all proteins have a _____ composed of protein and nucleic acid
virus
an infective agent that typically consists of a nucleic acid molecule in a protein coat that replicates in a host cell -broad term. any point during life cycle (inside or out. packaged or unpackaged)
host transcriptional machinery in the nucleus
because viral DNA resembles host DNA, a viruses can use _____
no, a virus is specifically targeting a specific host cell. it has certain proteins to attach to certain host cell receptors
can a virus infect any cell?
- +RNA: acts like mRNA in human cells and can be translated by the host cell - -RNA: cannot be translated by human cell, so virus must contain RNA polymerase to copy the RNA strand into a +RNA strand.
compare + and - sense RNA
-DNA: double stranded -RNA: mostly single stranded, but can be double
compare DNA and RNA in number of strands
-DNA viruses are transcribed in the nucleus and use host cell DNA polymerases -RNA viruses are translated in the cytoplasm and bring their own RNA polymerase
compare location of transcription and translation of DNA and RNA viruses
-glycoprotein on virus binds to host receptor -the viral glycoproteins promote membrane fusion so both cells become one giant cell -nucleocapsid expelled into cytoplasm -host cell is marked with residual viral glycoproteins now (how immune system can recognize viral infected cells)
explain the process of endocytosis for enveloped viruses in the viral replication cycle
-virus binds to surface protein -stimulates receptor mediated endocytosis -virus is internalized in a vesicle -virus is released into the cytoplasm to unpack
explain the process of endocytosis for naked and enveloped viruses in the viral replication cycle
intrinsic capsid antigenic and cytotoxic
fiber proteins on adenoviruses are _____ structures for human immune cells to recognize the virus. they are _____ and _____ are are grooves in the capsid durface
disassembled self-assemble
for viruses replication, the initial virus is _____ during the infection process and viral components must _____
nucleic acid
helical capsids are coiled springs shaped by _____
rod
helical viruses are _____ shaped.
they can be released by budding through the membrane or cell lysis (like naked)
how are enveloped viruses released
-size: nm to micrometers -morphology: nucleocapsid shape and envelope characteristics -nucleic acid type and structure of nucleic acid
how can a virus be classified based on structure
antibodies bind to the host cell receptors, blocking viruses from binding to the receptor, the virus can then be internalized into the cell to be neutralized -used in vaccinations
how can antibodies block the adoption process of viral replication cycle
they have a groove in outer protein layer to interact
how do naked capsid viruses interact with human cells
viruses steal the functionality of already existing receptors on host cells and make them receptors for the virus.
how do viruses obtain host viral receptors
they have early and late genes that are transcribed. early genes include encoding for DNA polymerases and DNA binding proteins (replication and regulatory transcription proteins). late genes encode for structural and other proteins (capsid proteins for packaging)
how is DNA viruses gene transcription temporally regulated
they must be copied to the positive strands before they can be translated, so they must pack their own active RNE dependent RNA polymerase enzymes because human host cells will not have it.
how is negative sense RNA viruses translated
naked or enveloped
icosahedrals may be _____ or _____
triangular capsid subunit assembly
icosahedron capsids have _____ shaped capsomeres like a multi-sided dice. it is shaped by _____
naked capsid virus enveloped virus
if a virus only has a nucleocapsid, then it is considered _____. if it has a nucleocapsid and glycoproteins and membrane (stolen membrane from human cells), it is _____
nucleic acids
in a helical virus, the _____ are in a spiral inside the hollow chamber of the protomers
nucleic acids enzymes nucleic acid binding proteins -everything needed for replication
in a naked virus, the outer layer of capsid protein encases _____, _____, and _____
replication
in enveloped viruses, they modify and use the cell membrane for the envelope during _____
naked
in general, are naked or enveloped viruses more stable
glycolipids co-opted
in the adsorption process of viral replication cycle. the initial attachment of the virus uses surface proteins, or _____, and the host cell receptors (inter grins and other surface proteins) are _____
virion viral genome
in the viral replication cycle, the uncaring process is the disassembly of the _____, separating the _____ from the envelope and capsid
virion
the complete, infectious form of a virus outside a host cell -seen in a microscope -packaged
persistent (latent) nucleus cytoplasm virion
many DNA viruses establish _____ infections. viral DNA genomes must enter and reside in the _____. the mRNA is exported to the _____, and then the proteins are transported into the nucleus for _____ assembly
ssRNA dsDNA
most common virus types are _____ and _____
more
naked capsids are _____ resistant than envelope
cell lysis -do not have a membrane to go through, so just burst out
naked capsids are released by _____
temperature pH proteases detergents drying
naked capsids are resistant to _____ (5)
recognition host entry
naked viruses have virion surface structures (spikes or binding grooves) for receptor _____ and _____
spike hemaglutinins (HA)
on an envelope virus, the host cell recognizes the glycoproteins _____ proteins embedded in the membrane. another example of oral attachment proteins (VAP) are one that bind to erythrocytes causing them to clump, they are called _____
small
picornavirus is a very _____ RNA virus
mRNA translated
positive sense RNA viruses are functionally the same as _____ and can be immediately _____
binding
spike proteins function for _____
protein membrane lipids glycoproteins
structural components of enveloped viruses
protein only
structural components of naked capsid
capsid
the _____ of a nucleocapsid is a structural protein coat
glycoproteins
the _____ of enveloped viruses help bind the nucleocapsid to the stolen membrane
capsid (assembly with nucleic acid and lips envelope)
virion shapes are determined by inherent _____ structure
nucleic acid protein
viruses exclusively us ghost cell machinery and resources for _____ and _____ production
make new copies spread
viruses only role is to _____ and _____
assembly
viruses reproduce by new _____ of component parts
living cell -obligate intracellular parasite requiring eukaryotic cell
viruses require _____ to replicate
arbovirus
viruses spread by biting arthropods (insects, ticks) -means of transmission
adenovirus
viruses that target lymphatic tissues
enterovirus
viruses that target the GI system
viral attachment proteins (VAP) or structures
what does the human immune system recognize on viruses
stolen membrane from host cells and glycoproteins
what is an virus envelope composed of
copy its genome and makes RNA
what is the first thing a virus does once it unpacks itself inside a host cell
from budding though the ER of the host cell, or directly from the host cells membrane
where does a virus get its envelope
they are tethered to the membrane of the virus as it passes through the ER in a host cell
where does the influenza virus obtain the hemaglutinin spike
they are mostly single stranded, so they do not have another strand to compare and ensure no errors were made during replication
why are RNA viruses more prone to mutations?
-in their simplest form, they are a nucleic acid and proteins (and maybe a capsule) -they have no metabolic function, so do not create now energy or utilization ATP
why are viruses not quite considered living
