Viral Structure and Multiplication

Question 1

what are the importances of viruses?

Answer 1

major cause of disease
important members of the aquatic world
important in evolution due to transfer of genes between bacteria
important model systems in molecular biology

Question 2

what are bacteriophages?

Answer 2

bacterial viruses

Question 3

what are the main types of viruses?

Answer 3

eukaryotic (plants, animals, protists, and fungi)

Question 4

how are viruses classified into families?

Answer 4

genome structure, life cycle, morphology, and genetic relatedness

Question 5

what is a virion?

Answer 5

mature viruses

Question 6

what do all virions contain?

Answer 6

a nucleocapsid composed of nucleic acid (DNA or RNA) and a protein coat

Question 7

what are capsids?

Answer 7

large macromolecular structures which serve as a protein coat of a virus

Question 8

what is the function of capsids?

Answer 8

protect viral genetic material and aid in its transfer between host cells

Question 9

what are capsids made up of?

Answer 9

protein subunits called protomers

Question 10

what are the three shapes of capsids?

Answer 10

helical
icosahedral
complex

Question 11

helical capsid characteristics

Answer 11

shaped like hollow tubes with protein walls

Question 12

icosahedral capsid

Answer 12

regular polyhedron with 20 equilateral faces and 12 vertices
capsomers are ring or knob shaped units made of 5 or 6 protomers

Question 13

complex capsids

Answer 13

do not fit into helical or icosahedral categories

Question 14

examples of complex capsids

Answer 14

poxviruses
large bacteriophages with final symmetry

Question 15

where do animal virus envelopes arise from?

Answer 15

lipids and carbohydrates from the host cell plasma or nuclear membranes

Question 16

how are viral envelope spike proteins made and what is their purpose?

Answer 16

encoded by the virus
involved in viral attachment to the host cell
used for identification of the virus
may have enzymatic activity
may play a role in nucleic acid replication

Question 17

how are viral genomes diverse?

Answer 17

viruses can be made of single stranded RNA, single stranded DNA, double stranded RNA, or double stranded DNA
the length varies from virus to virus
genomes can be linear or circular

Question 18

list the steps of the viral multiplication process

Answer 18

depends on viral structure and genome, but steps are similar:
1. Attachment to host cell
2. Entry and uncoating of genome
3. Synthesis
4. Assembly
5. Release

Question 19

what occurs during attachment (adsorption)

Answer 19

receptor determines host preference
-may be specific tissue
-may be more than one host
-may be more than one receptor

Question 20

what occurs during entry into the host?

Answer 20

the entire genome or nucleocapsid enters
varies between naked and enveloped viruses

Question 21

what are the three methods of host entry?

Answer 21

1. Fusion of the viral envelope with the host membrane; nucleocapsid enters
2. Endocytosis in vesicle; endosome aids in viral uncaring
3. Injection of nucleic acid (non enveloped)

Question 22

what occurs during the synthesis stage?

Answer 22

all viral components are produced
genome dictates the events
-RNA viruses must carry in or synthesize the proteins necessary to complete synthesis
genes and proteins may be referred to as early, middle, or late based on when they are synthesized

Question 23

what occurs during assembly?

Answer 23

putting together all components to make complete virions
assembly process is complex
baseplate, tail fibers, and components of bacteriophage T4 are assembled separately

Question 24

what occurs during virion release?

Answer 24

Non-enveloped viruses lyse the host cell
viral proteins may attack peptidoglycan or membrane

Question 25

how does virion release occur in enveloped viruses?

Answer 25

viral proteins are incorporated into the host membrane
nucleocapsid may bind to viral proteins
envelope derived from host plasma membrane, but may be Golgi, ER, etc.
Virus may use host actin tails to propel through host membrane

Question 26

what are the two types of phages and their reproductive choices?

Answer 26

virulent phage- multiplies immediately upon entry and lyses bacterial host cell
temperate phage- reproduce lytically as virulent phages do or remain in the host cell without destroying it

Question 27

what is lysogeny?

Answer 27

a relationship in which many temperate phages integrate their genome into host genome, making them a prophage in a lysogenic bacterium

Question 28

what is an advantage of a virus having a lytic cycle?

Answer 28

faster production, therefore there is faster infection

Question 29

what is an advantage of a virus having a lysogenic cycle?

Answer 29

if the environment is bad without other host cell options, the virus can stay and wait for another choice

Question 30

how does infection in eukaryotes work?

Answer 30

cytocidal infection results in cell death through lysis
persistent infections can last for years- chronic
the cell can transform into a malignant cell and cause tumor formation

Question 31

what are viroids?

Answer 31

infectious agents comprised only of RNA
typically targets plants
lacks an outer protein layer/capsid

Question 32

what are satellites (virusoids)?

Answer 32

infectious agents comprised of nucleic acids and a protein coat
needs a co-infector to replicate
can infect both plants and animals

Question 33

what are prions?

Answer 33

protein viruses that cause a variety of neurodegenerative diseases in humans and animals

Question 34

what are diseases caused by prions called and give examples

Answer 34

transmissible spongiform encephalopathies
-scrapies in sheep
-mad cow disease
-chronic wasting disease in deer
-kuru and Creutzfeldt-Jakob disease in humans