Chapter 3.23 Viral Replication and Taxonomy

Question 1

What are the unique characteristics of viruses?

Answer 1

They are energy-less
Have a protein coat (capsid) have no organelles or ribosomes
Have either RNA or DNA, never both!
Replication happens when virus takes control of host machinery

Question 2

What are the different shapes that the nucleic acid strands of a virus?

Answer 2

single-stranded, double-stranded, linear, or looped

Question 3

What are the 2 types of RNA viruses?

Answer 3

positive (+) and negative (-)

Question 4

What does a positive RNA virus mean?

Answer 4

RNA is just like the messenger RNA (mRNA)

When RNA virus enters host cell, it can immediately be translated

Question 5

What does a negative RNA virus mean?

Answer 5

RNA virus enters the cell but are not able to begin translation
*first must be transcribed into a positive strand of RNA

Question 6

How does a negative RNA virus transcribe into a positive RNA virus?

Answer 6

negative RNA viruses carry RNA-dependent RNA polymerase when carries out the transcription to positive strand
*human cells don’t have this polymerase so the virus must carry it

Question 7

What are the 2 special RNA viruses?

Answer 7

Retroviruses- can incorporate into host genome

Reoviridae- only virus with could stranded RNA genome

Question 8

What is the enzyme used in retroviruses?

Answer 8

reverse transcriptase

RNA –> DNA

Question 9

What strands do DNA viruses have?

Answer 9

negative and positive strand

Question 10

What is the difference between the negative and positive strands of DNA on a DNA virus?

Answer 10

Negative strand is the strand of DNA that is read and the positive strand is ignored
*Parvoviruses are the exception and have a single stranded DNA genome

Question 11

What are the 2 types of capsids of viruses?

Answer 11

icosahedral and helical

Question 12

What is a capsomer?

Answer 12

building block viral structure

Question 13

What is the shape of icosahedral virus?

Answer 13

20 equilateral triangles together

Question 14

What genetic material is always involved in the helical shaped viruses?

Answer 14

RNA

Question 15

What is the shape of a helical virus?

Answer 15

spherical shape

*except for rhabdoviruses which are bullet shaped

Question 16

What is the envelope of a virus made out of?

Answer 16

lipid bilayer membrane which the virus tore off the host

• viruses do not have to have membranes- viruses without membranes = naked
• viruses with membranes = enveloped

Question 17

How are viruses classified?

Answer 17

Nucleic acid, capsid, envelope, size

Question 18

What are the components of the nuclei acid classification of viruses?

Answer 18

type of nucleic acid- DNA, RNA
double vs single stranded
single or segmented pieces of nucleic acid
positive or negative stranded RNA
complexity of genome

Question 19

What are the 2 classifications of capsid viruses?

Answer 19

icosahedral or helical

Question 20

What are the 2 classifications of envelope viruses?

Answer 20

naked or enveloped

Question 21

What is the classification of shape of viruses?

Answer 21

Diameter of helical capsid viruses

Number of capsomers in icosahedral capsids

Question 22

What is the mneumonic for DNA viruses?

Answer 22

HHAPPP(y) viruses
Herpes
Hepadna
Adeno
Papoca
Parvo
Pox
(y)

Question 23

What is the most common classification of DNA viruses?

Answer 23

double stranded, icosahedral symmetry, replicate in the nucelus

Question 24

What 2 viruses are exceptions to the “most common” classification of DNA viruses

Answer 24

Parvoviridae- so simple that it only has a single strand of DNA- “ONE PAR” hole in golf
Poxviridae- extremely complex, has double stranded DNA but is not icosahedral, and replicated in the cytoplasm

Question 25

What 3 DNA viruses have envelopes?

Answer 25

Herpes Hepadna Pox

Question 26

What 3 DNA viruses are naked?

Answer 26

PAP
PApova, Adeno, PArvo
*women must get naked for their PAP smear exam

Question 27

What is the most common classification of RNA viruses?

Answer 27

single-stranded, enveloped, helical symmetry and replicate in the cytoplasm

Question 28

What are the exceptions to the “most common” classification of RNA viruses?

Answer 28

Reoviridae- double stranded
3 nonevneloped- Picorna, Calici and Reoviridae
5 icosahedral shapes- Reo, Picorna, Toga, Flavi, Calci
2 undergo replication in the nucleus- Retro and Orthomyxo

Question 29

What is the mneumonic for positive stranded RNA?

Answer 29

the CALCIfied old emperor PICO is wearing his CROWN(corona) and TOGA and is eating FLAVorful grapes from a RETRO bowl
(Calici, Pico, Corona, Toga, Flavi, Retroviridae)

Question 30

What is the mneumonic for negative stranded RNA?

Answer 30

Old Pete’s RABid dog FLIO fights paul BUNyon in the ARENA

Orthomyxo, Paramyxo, Rhabdo, Filo, Bunya, Arenaviridae

Question 31

What are the 4 steps of RNA viral reproduction?

Answer 31

1. Adsorption and penetration
2. Uncoating of the virus
3. Synthesis and assembly of viral products
4. Release of virions form the host cell

Question 32

What is the difference between Retroviruses and normal viruses?

Answer 32

retroviruses do not undergo immediate translation, the carry preformed RNA dependent DNA polymerase and are transcribed into the DNA
*directly incorporated into the host DNA

Question 33

What are the phases of DNA viral replication?

Answer 33

immediate early, early, and late transcription

Question 34

What is a naked virion?

Answer 34

cell that may lyse and release virions or virions may be released by exocytosis

Question 35

What is an enveloped virion?

Answer 35

initially naked but then acquired it’s envelope by budding through part of the host cell lipid bilayer as it exits

Question 36

What are the 4 host cell outcomes from viral infection?

Answer 36

Death- host cell’s own function shuts down resulting in cell death
Transformation- activation or introduce oncogenes causing uncontrollable cell growth
Latent infection- virus stays in “sleeping” state until reactivation
Chronic slow infection- virus that cause disease after many years