LEC 7 - Virus Structure + Function I Flashcards
What are all viruses when it comes to being a parasite?
Obligate Intracellular Parasites
What makes a virus a virus, making it different from bacteria?
No independent metabolism
Host provides ribosomes + energy + all precursor molecules
What does the small size of a virus allow for when it comes to entering a host cell?
Filterable agents
Passage through fine pore filters can occur
What is different about the viral replication when compared to other living organisms?
Progeny are created in an assembly line
Then quickly released into the host
NO BINARY FISSION
Latent period > Rise > Yeild
What is occurring in the cell during the latent period?
Replication
Assembly
What are viruses generally made of?
Nucleic acids
Proteins
Lipid-containing envelope
What is the principal component of a virus?
Proteins
What are the special enzymes that virus encodes for itself?
RNA dependent RNA polymerases for the negative strand RNA virus
Reverses transcriptase for retroviruses
Where are the special viral enzymes encoded?
Within the capsid
Term: Capsid
Protein covering surrounding core of nucleic acid + enzymes
Term: Capsomeres
Small protein subunits typically composed of several small proteins that combine in groups to form the capsid
Term: Virion
Complete virus particle
Term: Envelope
Membrane-like outer covering of certain viruses
Term: Spikes
Cirus proteins embedded in envelope that project from surface
What is the envelope made of?
Combination of host membrane with some virus proteins
What is often associated with spikes on a virus?
Enzymatic activities
What are the two patterns seen in the nucleic acid genome?
Extended nucleic acid form
Condensed nucleic acid form
What is the viral genome made of?
RNA
or
DNA
What are the forms of the viral RNA/DNA?
Double stranded
Single stranded
Segmented
Which is more stable, DNA or RNA?
DNA
What is the positive of having RNA as your genome?
Increased rate of replication
Which allows for more mutations, allowing the virus to adapt to the environment more easily
What are the characteristics of positive stranded RNA?
Can serve as mRNA directly
Directly translated by host ribosomes into proteins
Hosts understands
What are the characteristics of negative stranded RNA?
Must first be transcribed
Via virus-encoded RNA dependent RNA polymerase
Then becomes a positive strand
What is known about viral ancestory?
They do not share a common one
What are the two features that are used to discribe a virus?
Physical features
Biological properties
What physical features are used to describe virus?
Nature + Physical form of nucleic acid genome
Capsid structure + symmetry
Presence/absence of envelope
What biological properties are used to describe viruses?
Host range
Transmission mechanism
Tissue tropism
Pattern of replication
What phase must all virsuses pass through?
mRNA phase
What are the basic steps in viral replication?
Attachment
Latent period
Burst/Release by budding of progeny virions
What is occurring during the latent period?
Virus is developing inside the cell but is not readily evident outside the cell
What occurs with the cell when a true burst occurs?
Death of the host cell
Where do DNA viruses tend to repicate and mature in the host?
Within the nucleus
How do some DNA viruses disrupt the host cell cycle?
Change the control of p53 or Rb
Enters “S-like” phase to replicate
What is different about the replication process of large, complex DNA viruses?
Dont pay attention to host cell cycle
Supply their own host cell-independent DNA replication functions
Where does the virus go to be released out of the cell by exocytosis
Endoplasmic reticulum
Where do RNA viruses tend to replicate and mature in the host?
Cytoplasm
What is a common problem amoungst RNA viruses?
RNA is unstable
Molecules must be copied rapidly and the host doesn’t have the machienery to do so
What are the ways an RNA virus handles the issue of the host cell not being able to replicate it?
Transport molecules into the host in virion itself
– or –
Synthesized from virus genome
What are negative RNA strands need to be read?
RNA-dependent RNA polymerase (transcription)
How is RNA-dependent RNA polymerase made?
Place it within the capsid
Transport pre-formed into the host to start infection
What are the three viruses that can move retrograde through neurons?
Rabies
Herpes
Polio
What are the hallmarks of retroviral replication?
Reverse transcription
– and –
Integration
How are retroviruses handled within the host cell?
Pseudo-diploid RNA virus
Convert RNA to DNA (reverse transcription)
Term: Destructive replication
One double stranded DNA is substituted for two molecules of single stranded RNA that originally entered the cell
What enzyme does the retrovirus need that it encodes for?
Reverse transcriptase
(RNA-dependent DNA polymerase)
What does reverse transcriptase do?
Reverses the flow of genetic information
Allows DNA to be made from RNA
How does knowing the process of transmission lead to better control?
Effective control often hinges on breaking the chain of transmission
Term: Transformation (cancer + virus)
Host cells converted to malignant conditions
What does a host cell do to transform into a malignant condition?
Become immortal
Continue to divide w/o any control
Alter morphology
Lose contact inhibition
What are the critical mechanisms when it comes to a cell transforming into a malignant cell line?
Inactivation of cell cycle control mechanisms
Providing genese that alter host behavior
Enhancing transcription of key host genes involved in growth
Preventing host from inducing apoptosis
What cell types does transformation normally occur in?
Non-permissive host cells
What happens if the virus is able to proceed through a full growth cycle?
Host cell will die
How do DNA tumor viruses alter the funciton of p53 or Rb?
Produce proteins that antagonize the function of the proteins
Stopping them from suppressing growth
What are the “three” methods by which retrovirus transformation occurs?
Acute transforming retroviruses
Chronic transforming retroviruses
Indirect method
How does the indirect method of retroviral transformation occur?
Induction of tissue damage produces mutations
Describe: Chronic transforming retroviruses
Activate expression of growth-stimulating host genes
Slower induction of cancer
Describe: Acute transforming retrovirus
Bring in altered forms of genes involved in cell growth control
Drive host out of balance
Acute tumor induction
What are the oncogenes involved in acute transforming retrovirals?
ras
src
myc
jun
fos
