Ch 13 - Viruses, Viroids, Prions

Question 1

Characteristics of all viruses

Answer 1

1) Single type of nucleic acid only (either DNA or RNA, not both)
2) Protein coat, known as capsid and made of capsomeres
3) Obligate intracellular parasites (although, they aren’t the only ones; eg. chlamydia is a bacterium)
4) spikes (proteins for attachment)

Question 2

History: the first guy to display that viruses are transmissible b/ween plants (via Tobacco Mosaic virus)

Answer 2

Aldolf Mayer

Question 3

History: This guy wanted to filter tobacco mosaic virus through his porcelain filter. But alas, viruses are too small and he failed to filter them out.

Answer 3

Iwanoski

Question 4

FYI: E. coli is 3,000x1000 micrometers. Poliovirus is 30 micrometers

Answer 4

and bacterial phages are about 225 micrometers

Question 5

Bacteriophages have two variations of life cycle (upon infecting the host):

Answer 5

1. Lytic
2. Lysogenic

Question 6

Life cycle: Virulent phages, results in the lysis of the cell

Answer 6

Lytic

Question 7

Life cycle: May lyse but may also become a permanent part of the bacteria’s genetic makeup, within the chromosome

Answer 7

Lysogenic

Question 8

Productive infection

Answer 8

Phages infect bacterial cells, and new virions are created (could be the result of the lytic life cycle or the virus is shed from the host cell)

Question 9

Latent state

Answer 9

Phages enter bacterial cells, the virus integrates into the genome of the host cell and does not generate new virions.

Question 10

Filamentous phage (M13)

Answer 10

ssDNA that attach to F pilus
ssDNA -> dsDNA known as RF (replicative form)
One strand is for mRNA and the other is for more ssDNA

Question 11

Enveloped viruses contain an additional layer known as an “envelope” made of a ________. Envelopes are more common in animal viruses, not in phages

Answer 11

phospholipid bilayer

Question 12

Virus shapes:

Answer 12

-polyhedral
-helical
-complex (a combination of the two)

Question 13

Phage integrated into the bacterial DNA are referred to as:

Answer 13

prophage (like lambda)

Question 14

These phages, known as ____________, attach to E.coli via the F pilus and eject single-stranded DNA. A complementary strand is replicated, which then serves as a template for mRNA production and more single-stranded DNA. Forms more virus that ejected themselves from the cell.

Answer 14

Filamentous (eg: M13)

Question 15

Naked viruses tend to exit the cell via:

Answer 15

Lysis

Question 16

Two types of interactions that viruses have with animal host cells:

Answer 16

Acute infection
Persistent infection

Question 17

lying dormant or hidden until circumstances are suitable for development or manifestation

Answer 17

Latent

Question 18

Generalized transduction

Answer 18

Bacterial DNA only in the polyhedral head- no new viruses made by transduction particle

Question 19

Specialized transduction

Answer 19

Contains bacterial and viral DNA, can incorporate into genome, no new viruses made by the transduction particle

Question 20

Transformation

Answer 20

Uptake of naked DNA from the environment

Question 21

Congugation

Answer 21

Donor DNA from one bacterium to another via sex pilus

Question 22

Homologous Recombination

Answer 22

type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA

Question 23

T4 phage cycle stages

Answer 23

Lytic/virulent! Host: E.coli
1) attachment
2) genome entry
3) Transcript/translate
3) protein synthesis, DNA replication
4) assembly
5) release/lysis

Question 24

Lambda phage

Answer 24

Temperate virus. Host cell: E.coli

Latent/lysogenic life cycle
Lysogenic cycle happens when the circular viral nucleic acid (prophage) is incorporated into the DNA chromosome.

b/ween gal (galactose) and bio gene (biotin)

The prophage may excise itself spontaneously (UV) and start the viral synthesis process.

“Perks”:
Blocking of additional infection by same virus
Change in phenotype

Question 25

Lysozyme vs lysosome

Answer 25

Lysozyme: enzyme found that is capable of breaking proteins in the bacterial cell (lytic cycle)

Lysosome: is an organelle found in cells that consists of a large variety digestive enzymes. (phagocytes+lysosomes=phagozomes)

Question 26

Twort and d’Herelle

Answer 26

Identified the first bateriophages (bacteria viruses)

Question 27

Herpesviridae

Answer 27

dsDNA

Latent (can be present without disease) occurs and then reoccurs
Ex: chicken pox and reactivated as shingles, mono

Question 28

Persistant infections

Answer 28

Latent (Herpes, mono), chronic (Hep B), slow (retroviridae)

Question 29

Active

Answer 29

Short duration, long term immunity

Question 30

Hep B

Answer 30

dsRNA, enveloped, hepadnaviridae