Ch 13 study guide: Viruses, Viroids, and Prions Flashcards
What is the most basic structural definition of a virus?
Tiny infectious particle
Obligatory intracellular parasites
Know the 4 general characteristics of viruses
- contain single TYPE of either DNA or RNA
- contain protein coat
- multiple only inside living cells
- contain specialized structures
What is a virion?
complete, fully developed viral particle
What does it mean to be in the eclipse phase?
complete infective virions are NOT
present
Know the relative size of a virion compared to full cells.
Range from 20nm to 1000nm
What is a capsid?
-a protein shell or coat
-surrounds the genetic material
-protects the virus
-allows the virus ti infect new cells
What does the Tail Sheath in a virus do?
-acts like a needle and forces the genetic material into the host cell
What does the Base Plate in a virus do?
helps the virus attach to the host cell
What does the Tail Fiber in a virus do?
used to stabilize and attach to the host cell
What is the source of a viral envelope?
The viral envelope is derived from host cell membrane.
What is a spike composed of?
Carbohydrate-protein complexes that project from the surface of the envelope
What is a role of viral spikes?
- Attach to host cell
- Means of identification
What types of nucleic acid can be used for the viral genome?
DNA or RNA
What is the relative size of the viral genome?
Range from 20 nm to 1000 nm in length
What are the two possible viral life cycles?
Lytic and Lysogenic cycles
Know the steps of the lytic life cycle.
- Attachment
- Penetration
- Biosynthesis
- Maturation
- Release
What components of the host cell are required (highjacked) by the virus to complete the viral life cycle (think of a few examples)?
chromosome
What is a provirus vs a prophage.
Provirus infects a eukaryotic organism. Prophage infects bacteria.
What is a prophage?
A prophage is the genetic information of the virus after it has been inserted and incorporated into the bacterial DNA which can leave spontaneously
What is a provirus? When is a provirus used?
Never comes out of chromosome
Only used in ANIMAL viruses
Which can excise from the host’s genome?
the action of UV light, or chemicals can lead to excision of phage DNA
Can provirus genes be used by the host cell?
Yes
When does a prophage become active again?
Spontaneous event, the action of UV light, or chemicals can lead to excision of phage DNA
Can a cell infected with a provirus be attacked by virions of the same type?
Lysogenic cells are immune to reinfection by the same phage.
How does specialized transduction differ from generalized transduction?
Specialized -the bacteriophages pick up only specific portions of the host’s DNA.
Generalized - can pick up any portion of the host’s genome
The life cycle of viruses that infect animal cells is very similar to that of phages. What are some of the key differences between the two?
Lytic cycle: varion factory and leads to the death of the host
Lysogenic cycle: leads to integration of phage into the host genome. Doesnt kill host
What is special about Retroviruses? What is the name of the important enzyme?
They use a special enzyme called reverse transcriptase to translate its genetic information into DNA.
what can happen to the provirus of an infected cell?
replicate while it is still incorporated in the host cell’s genome.
What is a prion?
Short for Proteinaceous infectious particle
They are misfolded protein
What is the mechanism for prion-based diseases?
Conversion of normal host glycoprotein PrPC
into PrPsc
What are the general characteristics of a prion-caused disease?
tremors
uncontrillable laughing
What does the abbreviation CJD stand for?
Creutzfeldt-Jakob disease
What is a viroid composed of?
short strand of circular, single-stranded RNA that has no protein coating RNA
What do viroid’s infect?
Plants
Describe why viruses are considered not complete independent cells
- Viruses need a host cell to replicate
- Cant generate their own food
- Uses a lot of the host cells compontets to completely replicate
What is an advantage of using bacteriophages as a form of therapy?
Shown to effectively fight and destroy multi-drug resistant bacteria. Namely, when all antibiotics fail, phages still succeed in killing the bacteria and may save a life from an infection.
What is the full name for tRNA and what is its function?
Transfer RNA
Bring over amino acids to match up with its corresponding codons to make a protein
Retroviruses is an RNA virus that uses and enzyme called
Reverse transcriptase to make double stranded DNA
EX: hiv
RNA-dependent RNA polymerase is used for
making more RNA for their capsids, they then use the rest of the host cells machinery for biosynthesis
What is a bacteriophage?
viruses that infect bacteria
Does a bacteriophage go through the lytic or lysogenic cycle?
both
What part of the virus contains the viral nucleic acid?
Capsid
Which bacteriophage life cycle has a prophage?
Lysogenic
True or False
Antibiotic resistance in a bacterium happens after after an antibiotic has been given
False
What are some genetic recombination processes that can result in a bacteria having a new trait such as antibiotic resistance or toxic production?
- Conjunction
- Transduction
- Transformation
-Transposons
What involves bacteriophages packing up bacterial DNA and transferring it to another bacterial cell?
Transduction
name two differences between animal viruses and bacteriophages
animal viruses infect animal cells while bacteriophages infect bacterial cells
animal viruses (specifically retroviruses) can form a permanent provirus within the animal’s chromosome. while bacteriophages form prophages within bacterial chromosomes that can be excised spontaneously
describe why viruses are considered not complete independent cells?
viruses need a host cell to replicate
they do not make any/enough of their own enzymes/nucleotides/ribosomes to replicate on their own
