Chapter 3 Flashcards
What are the three primary components of a virus particle?
viral nucleic acid, capsid, and lipid envelope
What is a virus particle also known as?
virion
True or False: All viruses are composed of RNA.
False: viruses can be composed of either RNA or DNA
Are viruses haploid or diploid organisms?
haploid
Define capsid.
a protein shell that surrounds the viral nucleic acid (genetic material) of the virus
What is the capsid composed of?
smaller repetitive protein subunits termed capsomers
True or false: All viruses have the lipid envelope
false
What is the lipid envelope made up of?
a lipid bilayer derived by budding from a host cell membrane and is embedded with glycoproteins
What is a capsomer?
identical protein subunits that make up the capsid
What makes up a capsomer?
1 to 6 or 7 individual proteins called protomers
What are the two basic types of capsid symmetry?
Icosahedral and helical
Describe the Icosahedral shape.
closed structure composed only of a single repeating subunit
All animal viruses with helical symmetry are _____ ___ __ _______.
surrounded by an envelope
What are the three functions of the capsid?
- Protects the nucleic acid
- Interacts with viral and cellular proteins to promote packaging of the viral genome and assembly of the virus particle
- Interacts with cellular proteins during virus entry and exit from the cell
How is a viral envelope acquired?
by budding through a host cell membrane (usually a plasma membrane)
What is the function of the glycoprotein molecules in the viral envelope?
facilitate entry and exit from the host cell
What is a peplomer?
glycoproteins contained within the envelope
What are the three structural proteins of a virion?
matrix, nucleocapsid, and tegument
Define matrix.
non-glycosylated proteins found on the inner layer of the envelope
Define nucleocapsid.
the protein layer surrounding the viral genomic nucleic acid
In many cases, what is the nucleocapsid?
the capsid protein
Define tegument.
an amorphous protective protein layer between the capsid and envelope of herpes viruses
Give examples of 2 non-structural proteins.
polymerase and regulatory/accessory proteins
What is a polymerase?
virus-encoded enzymes required for biosynthesis viral nucleic acid and proteins
What is the function of regulatory/accessory proteins?
function to provide intracellular environment that promotes biosynthesis of viral proteins and nucleic acid
Are enveloped viruses or non-enveloped viruses more fragile?
enveloped
Why are enveloped viruses more fragile?
- more heat liable
- more susceptible to freezing and thawing
- more susceptible to desiccation
What is a viral serotype?
a set of viruses that can be distinguished from other viruses in the same species on the basis of antigenic properties
What is a ‘strain’?
a term used to denote different viruses of the same serotype, but with only minor differences in biological phenotype
What is an ‘isolate’?
sample of a virus from a single, defined source
What are most viruses transmitted by?
inhalation, ingestion, injection, close contact, or congenitally
Define respiratory viruses.
term is usually restricted to viruses that remain localized in the respiratory tract, rather than causing generalized infections
Typically, how are respiratory viruses acquired?
inhalation or fomites
Define enteric viruses.
term usually restricted to viruses that remain localized in the intestinal tract, rather than causing generalized infections
Typically, how are enteric viruses acquired?
by ingestion (and replicate in intestinal tract)
Define arbovirus.
an arthropod-borne virus that replicates in blood-feeding arthropod vectors and is transmitted by bites to vertebrate hosts
What are oncogenic viruses?
viruses that usually infect specific cells, where they become persistent and may evoke transformation
What questions need to be answered for classification of viruses at the family level?
- What type of nucleic acid does it have?
- Does the virus have an envelope?
- Is the viral genome segmented or not?
