viruses Flashcards
How does a bacteriaphage infect its host?
The protein capsid contains virus DNA or RNA and it this genome is injected into the cell of the bacteriophage (cell)
What is the most common way phages exit host bacterium?
cell lysis
Describe lysis - for phage exiting host bacterium
endolysin, is coded for in the viral nucleic acid of lytic phage
Endolysin attacks and breaks down bacteria’s cell wall peptidoglycan
Infected bacterium is destroyed as a result.
Describe basic steps of the lytic cycle of bacteriophage
- entry
- releases enzyme to break up host genome
- uses host genome to make it’s own material
- gets assembled
- enough are made lysis occurs
lysogenic cycle
ability of bacteriophage to integrate it’s genome into the host’s cell
- some bacteria have the ability to take their genes and work them into the bacterial chromosome (red-blue double circle)
- produces bacterial and viral DNA
what are viruses made of?
nucleic acid, proteins, and s/m lipids
describe a capsid of a virus
Nucleic acid surrounded by a protective protein coat, called a capsid.
describe envelope of a virus
Some viruses have an outer membranous layer, called an envelope, made of lipid and protein, surrounds the capsid in some viruses.
do all viruses have envelopes?
no
what is a difference between a naked and enveloped virus structure?
an enveloped has an envelope with spikes embedded into it (glycoproteins)
How do viruses differ from living organisms?
Viruses are not living organisms because they are incapable of carrying out all life processes
list characteristics of life that viruses do not conform to
- are not made of cells
- can not reproduce on their own
- do not grow or undergo division
- do not transform energy
- lack machinery for protein synthesis
do viruses have more variety in nature of their genomes than do cells?
yes ; although much smaller than genomes of cells
can be dsDNA, ssDNA, dsRNA, and ssRNA
may be linear and composed of several segments or single and circular
the viral capsid function b/c it has a protein. coat
Protein coat provides protection for viral nucleic acid and means of attachment to host’s cells.
The viral capsid is composed of protein subunits called
capsomeres
capsids are composed of single type of capsomere while others are composed of multiple types; T or F
true
How is the viral enveloped acquired?
Acquired from host cell during viral release; envelope is portion of membrane system of host.
If the viral envelope is taken from an infected cell’s plasma membrane, what macromolecule is the viral envelope primarily made of?
Also contains proteins and virally-coded glycoproteins (spikes).
Envelope’s proteins and glycoproteins often play role in
host recognition
If a virus doesn’t have an envelope,it is considered to be a
naked virus
What is an advantage of having a cell envelope?
- wouldn’t be picked up by immune cells (protection) invisible cloak
- doesn’t require any work - just steals it (steals part of host for it’s own use)
How do viruses exit the cell?
lysis or budding
lysis = naked cell
budding = enveloped cell
How does a virus recognize & attach to its host?
Adsorption
Adsorption
The general phases in the life cycle of animal viruses are adsorption, *penetration, synthesis, assembly, and release from the host cell
why do most viruses infect only a certain type of host?
Specificity due to affinity of viral surface proteins to proteins on the surface of the host cell.
what characteristics bacteroiphages have that are attracted to proteins on the surface of bacterial cells?
bacteroiphages have proteins in their tail fibers (those extensions that look like legs)
What characteristics do animal viruses have that are attracted ot the glycoproteins on the surface of animal cells?
animal viruses have proteins or glycoprotein spikes that correspond to glycoproteins on the surface of animal cells.
Virus exist outside and inside its host true or false
true
what is the extracellular state called when a virus infects its host?
virion
What is composed of the virion?
- protein coat (capsid) surrounding nucleic acid
- some have phospholipid envelope
what is the outermost layer function for host cells?
Outermost layer provides protection and recognition sites for host cells
How does a virus infects its host intracellular state?
capsid removed
virus exists as nucleic acid (genetic material)
How does an animal virus infect its host? (2)
- Direct penetration of naked virus (Viral genome enters cell, while capsid remains on cell’s surface.)
- endocytosis
what are three examples of animal virus entry?
influenza
herpes simplex virus
HIV/AIDS virus
does viral genome have DNA, RNA, BOTH?
EITHER BOTH NEVER BOTH
Pre-formed enzymes required for viral replication: polymerase function
DNA or RNA
Pre-formed enzymes required for viral replication: Replicases
copy DNA
Pre-formed enzymes required for viral replication: reverse transcriptase
synthesis of DNA from RNA
When new animal viruses exit host cell it depends on what?
Depends whether or not they have an envelope.
how do naked viruses exit the host cell?
After construction of capsid, naked viruses may be released from animal cell through exocytosis or may cause lysis and death of cell.
how doe enveloped viruses exit the cell?
- Often released through a process called budding
- Virus exits cell with part of cell’s plasma membrane.
Cytopathic effects
cell damage altering microscopic appearance
what type of changes can cytopathetic effects cause?
- Disorientation of individual cells
- Gross changes in shape or size
- Intracellular changes (inclusion bodies, syncytium)
How long is latency of viruses? some can remain dormant
can remain for years with no (little) viral actiivty
what do retroviral provirus do? ex. disease
Retroviral provirus incorporates into host DNA (HIV)
Some latent viruses do not incorporate - name an example
herpes
what type of virus is influenza?
RNA virus and segemented
For influenza, where do viruses attach to and multipies?
respiratory tract
How does influenza enter the nucleus?
segments of RNA genome enter the nucleus
how does influenza assemble and leave the cell?
finished viruses are asembled and bud off the cell
INFLUENZA IS ENVELOPE
RNA genome increases the risk of what
mutation
What is key to influenza?
glycoprotein spikes like Hemagglutinin and Neuraminidase
Hemagglutinin - how many subtypes?
15 subtypes
Hemagglutinin function
binds to host cell; virulence factor (most important)
Neuraminidase - how many subtypes?
9 subtypes
Neuraminidase function
hydrolyzes mucus and assists viral budding and release
Both glycoproteins, H and N, frequently undergo genetic changes, which decreases what?
the effectiveness of the host immune response
Why makes influenza hard for memory cells to recognize?
high rate of mutation (RNA) - changes a lot —- akd antigentic drift
antigenic drift
constant mutation – gradually change their amino acid composition
antigenic shift
one of the genes or RNA strands is substituted with a gene or strand from another influenza virus from a different animal host
what two things influence Influenza mutation?
antigenic drift
antigenic shift
What is the most virulent influenza strand?
Influenza A
After 2003, strains of influenza A viruses that usually infect birds underwent an antigenic shift and began to infect humans
what influenza strand undergoes antigenic drift but no antigenic shift?
Influenza B
What influenza strand is known to only cause minor respiratory disease; probably not invovled in epidemics?
Influenza C
Where does influenza A bind to?
Binds to ciliated cells of respiratory mucosa
Causes rapid shedding of cells, stripping the respiratory epithelium; severe inflammation
symptoms of influenza A
Fever, headache, myalgia, pharyngeal pain, shortness of breath, coughing
